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E GO R0fl0Servicing &Technology January 19861$2.25

Horizontal, high voltage, vertical problems of the CTC109

Video color camera repair, 2 Microcomputer troubleshooting, 3

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The how-to magazine of electronics...

GIGOTIIOAIOVolume 6, No. 1 January 1986

8Horizontal, high -voltageand vertical problemsin the RCA CTC109ABy Homer L. DavidsonStep-by-step procedures forcorrecting this model'sfunctional aberrationscommonly related to theabove problems.

20Introduction tomicrocomputertroubleshooting, part 3By Bud Izen, CET/CSMAgain, the relaxed approachis emphasized as the authordescribes the fundamentalsof troubleshootingtemperamental disk drives.

28Test your electronicknowledgeBy Sam WilsonReaders can answer these10 questions by diggingdeeply into memory banksof general, not necessarilybasic, information.

38Repairing the consumercolor video camera, part 2By Neil HellerUnderstanding and using thetools provides the focus forthis month's continuation ofthe series.

46What do you know aboutelectronics? Receiversand bidirectional busesBy Sam WilsonWhether approached asbrand-new information or torefresh existing knowledge,Wilson's summarization ofradio receivers (crystal tohomodyne) and the 2 -waybus makes interestingreading.

Departments:4 Editorial6 Technology

37 News57 Photof act58 Troubleshooting Tips59 Products60 Books61 Literature62 Reader's Exchange

Because of the implications for theentire TV industry, ES&T details thetechnology of the LCD TV -screen,beginning on page 6, comparing thisscreen with conventional CRTs. Toparaphrase an editorial headline fromthe May 1985 issue, "It's all happeningso fast!"

It's not a pretty picture when C105, theonly rectified -line -voltage filtercapacitor, is open in the CTC109A. Thearticle begins on page 8.

2 Electronic Servicing & Technology January 1986

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Editorial'vw

Picture a new era in televisionTelevision has experienced many changes and

refinements in the decades since it was introduced.Even though a TV set of today does essentially thesame things that early sets did, they do it so muchbetter. For example, in those early sets, thebrightness left a lot to be desired. The room had tobe darkened to view the picture satisfactorily, and abright daylight -lit room severely washed out the pic-ture. Today's sets can be viewed in direct sunlight.

At the same time, as pictures were gettingbrighter, they were getting bigger. The small pic-ture tube of decades ago has grown to 19, 21, 25inches, and even larger. Further refinements havegiven us TV sets with beautiful color pictures,smaller size, lighter weight, greater reliability,lower power consumption and better sound quality.The list goes on and on.

A casual look inside a modern TV set compared tothe insides of an early set will reveal many changesin technology, components and construction thathave made these advancements possible. In old sets,you'll find vacuum tubes, their filaments gobbling uppower, taking up lots of space and generating a lotof heat. In the modern set, all of the electronic func-tions are performed by semiconductor devices: tran-sistors and ICs. Printed circuit boards in the modernset have replaced the old, large, heavy metal chassisand point-to-point wiring.

It doesn't take an expert to see that one thinghasn't changed. There's still that heavy, bulky CRTtaking up a lot of space, requiring high voltage andpresenting an implosion hazard any time servicingrequires attention to it. To be sure, the picture tubein the modern set is technologically advanced far

beyond that of the CRT in the older set; still, it justseems that compared to the advances in every otherarea of the new set the picture tube is ananachronism.

That might just change. LCD technology hasrecently been advancing at an incredible rate andholds promise to be a candidate to replace CRTs.Already, LCDs have been used in both monochromeand color hand-held TV sets. So far the picture quali-ty leaves a lot to be desired, but the mere fact that ithas been done is impressive. And the manufacturersof LCDs are diligently working to advance the stateof those devices to the point where they will be ableto compete with CRTs in terms of quality, reliabilityand cost. The article beginning on page 6 describesthe state of the art as it stands today.

The possibility that one day, perhaps soon, theCRT will be replaced by LCDs starts one thinkingabout the implications for servicing. The first thingthat comes to mind is that here's another newtechnology to be learned through a lot of hard work;and there's merit in that thought. But think of thegood side of it: There goes the high voltage, thepossibility of getting bit by 30,000 -odd volts; nomore high -vacuum device just waiting for you to becareless with a screwdriver or pair of pliers; no moreflyback transformers, and no more retrace lineswhen things aren't working properly. If LCDsultimately do replace CRTs, TV servicing really willbe a brand-new ball game.

et,J e41.0%4.01

ELECTRONIC

Editorial, advertising and circulation cor-respondence should be addressed to: P.O. Box12901, Overland Park, KS 66212-9981 (a suburbof Kansas City, MO); (913)888-4664.

EDITORIALNils Conrad Persson, EditorCarl Babcoke, Consumer Servicing ConsultantRhonda L. Wickham, Group Managing EditorMarjorie Riggin, Associate EditorJoy Culver, Editorial AssistantDarrylI Fortune, Editorial Assistant

BUSINESSCameron Bishop, Group Vice PresidentEric Jacobson, PublisherGreg Garrison, Sales ManagerStephanie Fagan, Promotions ManagerKelly Hawthorne, Marketing AssistantDee Unger, Advertising SupervisorKaren Royal), Advertising Coordinator

ARTKevin Callahan, Art DirectorJoni Harding, Graphic Designer

ADMINISTRATIONR. J. Hancock, PresidentJohn C. Arnst, Circulation DirectorEvelyn Rogers, Circulation ManagerDee Manies, Reader Correspondent

eMP

Member, Audit Bureauof Circulation

Member, AmericanBusiness Press

ELECTRONIC SERVICING & TECHNOLOGY (USPS 462-050)

(with which is combined Electronic Technician/Dealer) ispublished monthly by Intertec Publishing Corp., 9221Ouivira Road, P.O. Box 12901, Overland Park, KS

66212-9981. Second Class Postage paid at Shawnee Mis-sion, KS 66201. Send Form 3579 to P.O. Box 12952,Overland Park, KS 66212-9981.

ELECTRONIC SERVICING & TECHNOLOGY is the "how-to"magazine of electronics. It is edited for electronic profes-sionals and enthusiasts who are interested in buying,building, installing and repairing consumer electronicequipment. This includes audio and video equipment,microcomputers and electronic games.

SUBSCRIPTION PRICES: one year $18, two years $30.three years $38 in the USA and its possessions. Foreigncountries: one year $22, two years $34, three years $44.Single copy price $2.25; back copies $3.00. Adjustmentnecessitated by subscription termination to single copyrate. Allow 6 to 8 weeks delivery for change of address.Allow 6 to 8 weeks for new subscriptions.

PHOTOCOPY RIGHTS: Permission to photocopy for internalor personal use is granted by Intertec Publishing Corp. forlibraries and others registered with Copyright ClearanceCenter (CCC), provided the base fee of $2 per copy of arti-cle is paid directly to CCC, 21 Congress St., Salem, MA01970. Special requests should be addressed to Eric

Jacobson, publisher.ISSN 0278-9922 $2.00 + 0.00

/NTERTEC/UILNNING CORPORATION

',1986 All rights reserved.


How to beat the high costof cheap meters.

IN THE U.S. AND NON -EUROPEAN COUNTRIES: John Fluke MI Co. Inc., PO Box C9090, M/S 250C. Everett, WA 98206. Sales: (206) 356-5400, Other (206) 347-6100EUROPEAN HEADQUARTERS: Fluke (Holland) Fl V.. PO Box 2269. 5600 CG Eindhover, The Netherlands. (040) 458045, TLX 51846

© Copyright 1985 John Fluke M15. Co., Inc. All rights reserved. Ad No 4714-70

You get what you pay for.

So get the Fluke 70 Series.You'll get more meter for your money,

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FLUKECircle (5) on Reply Card

January 1986 Electronic Servicing & Technology 5

The cathode-ray tube has beenthe standard display for elec-tronics applications for more than45 years. Today, however, in thoseapplications where the CRT haswell-known drawbacks - large size,weight, fragility and a require-ment for high voltages -flat-paneldisplay technologies are challeng-ing the supremacy of the long-standing CRT.

This article was adapted from information presentedby Epson America, Torrance, CA, at seminars held InOctober 1985 in New York City and San Jose, CA. Allart is courtesy of Epson. Papers Included In this arti-cle were presented by Toshiaki Salto, Director ofResearch and Development; Yoshio Yamazaki,General Manager, Fundamental Technology Researchand Shinji Morozuml, Manager of FundamentalTechnology Research.

LCD rivals CRT

The major flat -panel technolo-gies competing with the CRT in-clude: thin-film electrolumines-cent, known in the industry as EL;plasma display panels, known asPDP; vacuum fluorescent displays(VFD); and liquid crystal displays,or LCDs. Each technology offersunique strengths and weaknesses.None of them offers a perfect solu-tion for every application.

The popularity of personal com-puters has created a strong de-mand for these alternative (non -CRT) display technologies, andstimulated rapid advances in flat -panel display technologies over thelast two or three years. Flat -panel

displays have exhibited im-provements in performance,especially in terms of cost-effective LCDs.

A history of LCDA number of existing LCDs are

already being used to satisfy theneeds of the personal/portablecomputer market. The struggle isto provide a suitable display,regardless of the technology. Forany kind of display device the fun-damental question is: How muchinformation can be displayed in agiven area?

First generation LCDs, in-troduced between 1975 and 1979,


were developed for wristwatchesand calculators. These displays areextremely low cost and feature lowpower consumption and simpleconstruction, making them idealfor high -volume production. Today,the annual production of digitalwatches is about 200 million, near-ly half of the total watch volume.Another 120 million LCDs areused annually in calculators.

These displays are useful onlyfor displaying simple numerals,however, and have limited applica-tion for computers.

Second generation LCDs, in-troduced in 1980, proved perfectfor displaying alphanumericcharacters and some graphics sym-bols; these displays work well ininformation -display panels such asfound on audio equipment anddomestic electrical appliances.

Third generation LCDs are juststarting to appear. Featuringrelatively large display area withhigh resolution, this generation iswell suited for alphanumeric andgraphic displays and high -resolution dot-matrix images suchas needed for hand-held computersand color TV displays.

Simple matrix displaysThe simple matrix liquid crystal

display demonstrates the basicoperating principle of all LCDs.The display consists of two glasssubstrates containing transparentelectrodes, with the liquid crystalmaterial sandwiched betweenthem (Figure 1). The electrodescontrol the arrangement ofmolecules in the liquid crystalmaterial that, in turn, controls thepassage of light through the cell.The simple construction of thisdisplay makes it inexpensive toproduce-a major reason for itsrapid growth in the displaymarket.

The basic principlesof LCD operation

Liquid crystal material is anorganic liquid that has the opticalproperties of a crystal. Thismaterial is convenient for use inmaking displays because themolecular structure of the liquidmakes it easier to control theorientation of molecules than itwould be in a crystal. Each orien-tation of molecules represents aparticular liquid -crystal phase, andeach phase affects the passage of

light through it differently. Con-trolling the phase of a given liquidcrystal material by means of avoltage applied to electrodestherefore controls the flow of lightthrough the cell.

Although there are more than 10liquid -crystal phases, many aren'tefficient for displays; some are inearly development and some aretoo complex to construct to beuseful for commercial products.Three types are commonly used:dynamic scattering, known as DSor DSM for dynamic scatteringmode; guest host, known simply asGH; and twisted nematic, whichengineers refer to as TN.

Dynamic scattering mode (DSM)Dynamic scattering mode

displays were the first practicalLCDs. Based on nematicmaterials, these displays are wellsuited for use in watches,calculators and other applicationsthat don't require a fast responsetime.

When an electric field is appliedacross a layer of nematic liquidcrystal material, the molecules

orient themselves to the field. Ifyou apply a sufficiently strongfield (e.g. 1V/micron), the ion flowgenerates a strong turbulence,producing a white opaque ap-pearance similar to frosted glass,as you see in Figure 2.

Guest host modeIn GHM displays, a dye is

dissolved in a positive liquidcrystal matrix. The dye has dif-ferent optical characteristicsparallel and perpendicular to itsaxes and can be aligned by interac-tion with the liquid crystalmolecules. The dye has its max-imum absorption when the electricfield vector is parallel to the axis ofthe molecules (Figure 3). Usingpolarizers to direct the light pro-duces an effect called switchedlight absorption.

This type of guest -host displayhas a wide viewing angle,brightness and good colorbrightness. You can expect to seeit used regularly in automobile ap-plications. (See Technology, ES&TSeptember 1985.)

Continued on page 50

LIQUID CRYSTAL

ELECTRODE (X)

GLASS SUBSTRATE

SPACER

ELECTRODE (Y)

GLASS SUBSTRATE

Figure 1. A simple matrix liquid crystal display consists of two glass substrates con-taining transparent electrodes with liquid crystal material sandwiched between.


Horizontal,high -voltage .. .

. . . andvertical

problems

in theRCA

CTCIO9A

By Homer L. Davidson

Perhaps 80% of color -TV chassisproblems are found in horizontal,high voltage and vertical circuits.GER versions of the RCACTC109A chassis have remote -control systems. Service records inthis shop suggest that the hori-zontal -output transformers in theGER models have failed often withless than two years of operation.Other CTC109 common problemswill be covered as the subjectscome up.

Overload conditionsSymptoms of no raster, no sound

and no high voltage usually in-dicate an overload of the regulated+ 120V source (Figure 1) that hasblown fuse F101, blown open fusi-ble resistor RF101 and caused allreceiver functions to stop. After anew RF101 resistor and a new fusehave been installed, check for ob-vious shorts. When you're satisfiedthat there are no shorts, apply acpower for just a couple of seconds.If the 5A fuse blows, suspect aleaky horizontal -output transistor.Measure the resistance betweencollector/case and ground. A goodtransistor should gradually in-crease to several hundred thou-sand ohms, while a leaky onemight check 4011 to 7011.

After the new output transistorhas been properly installed,remove the 5A fuse and connect a100W incandescent light bulbacross the terminals, (shownon page 9). This test bulb willlimit the transistor current to lessthan 1A, while reducing the acvoltage. Also the bulb brightnessshows the relative amount of cir-cuit current.

The on/off switch relay inremote -control models willnot switch on when low -input acvoltages are suplied for tests.Locate the on/off relay on thetuner -control chassis and look fortwo wires, one solid red and onewhite with a red stripe. Connect ajumper between the lugs wherethese two wires are connected(Figure 2). This will keep the acpower flowing to the bridge rec-tifier, even when it is only 80Vacor so.

Watch the light bulb and run theseveral minutes.

Measure the Q412 horizontal -output collector voltage. A muchhigher -than -normal reading mightindicate Q412 is open or SCR101 isleaky or shorted. Low collectorvoltage might indicate a leaky out-put transistor or damper diodeCR405 or perhaps leakage toground in the flyback.

After any necessary repairshave restored proper operationwith the light -bulb current limiter,disconnect the light bulb and in-stall a proper 5A fuse for finaltests at full voltage and current.

Defective flyback symptomsSome flyback problems can be

located by sight or sound, withouttest equipment. If the horizontal -output (flyback) transformer feelsvery warm it might indicateleakage between windings, or ex-cessive reverse current throughsome of the internal high -voltagediodes. A burned or raised area ofthe plastic outside covering in-dicates the transformer is defec-tive. A loud crackling or poppingnoise before shutdown indicates aleaky transformer, (photo, at top,page 10).


OPEN

F101SA L101

120VAC =\P-----10001

Figure 1.

bbb

S4201 RF101OPEN

ON-OFF óW

C1010.22"

o

L105

CR101 I680pF

= CR102= CR104I

CR103 * 680pF,

CTC109 PRIMARY POWER

C105.600NF`J

+162VSOURCE

Figure 1. F101 and surge -resistor RF101are the most likely power -supply com-ponents to blow when serious overloadsoccur. The + 162V supply is connectedto the SCR regulator that is supposed toproduce + 120V, regulated. Any of thefour bridge rectifiers (CR101 throughCR104) can be shorted by transientsentering on the ac line. It is wise tocheck them.

When suspicion falls on the flyback areaof the horizontal sweep circuit, it is goodprotection to remove 5A F101 and con-nect a 100W light bulb across the ter-minals. This limits the current to lessthan 1A while it reduces the voltage instep with current increases, protectingmost components. The brightness of thebulb gives an indication of the current.For example, the bulb was bright, so thehorizontal -output transistor was re-placed, but the bulb remained bright.Then, suspect a leaky horizontal -outputtransformer (flyback).

TO CONTROL CIRCUITS

Figure 2.

TWO RED

120VINPUT

RELAY ONREMOTE CONTROL

MODULE

WHITEWITH

RED TRACER

ADD TEST LEAD

ELIMINATE REGULATION AS TEST

Figure 2. The GER remote -control -equipped CTC109s might not turn on atthe low ac voltages used for tests.Therefore, a jumper wire should beplaced across the relay contacts to pro-vide ac voltage at all times.

If you replace the horizontal -out-put transistor and it is instan-taneously destroyed when power isapplied, replace the flybacktransformer. In that situation, thetransistor probably has internalleakage between collector andemitter (ground).

Replace the flyback when ex-cessive horizontal squeal is heardfrom it. Large arc lines in theraster might indicate a defectiveflyback with internal arcing.

Identifyinga defective flyback (or IHVT)A variable ac -power transformer


Sometimes a wisp of smoke might come from a leaky flyback, or a loud crackling orpopping noise might be heard before shutdown. This is almost certain proof of adefective flyback.

T101

+162V

T402

FLYBACK

L106

SCR101

12

13C1224700pF

{j

R121330lOW

C112C113 0.001 C106

C 0. 001- 1. 5NF

TESTSHUNT

+120VREGULATED

ADD SHUNT FOR LOW -AC -VOLTAGE OPERATION

Figure 3. To disconnect the SCR regulator during tests, add a jumper wire betweenanode and cathode of SCR101. Better yet, solder a short piece of hook-up wire be-tween those two SCR terminals; this prevents loose connections, shorts or arcs.

is recommended to supply lowerthan 120Vac line voltage to colorreceivers during tests of the hori-zontal -output transistor and theSCR voltage regulator. First,replace the fuse, fusible resistorand horizontal -output transistor.

Defeat the SCR regulator byshorting across SCR101. To pre-vent clip leads from movingaround and possibly shorting toother components, just solder ashort piece of hookup wire fromthe anode to the cathode terminalof SCR101 on the wiring side ofthe board (Figure 3). Plug thetelevision into the variable -voltagepower transformer. Starting at alow voltage, such as 40Vac, slowlyincrease the ac voltage until the+ 120V source measures about+ 75V or + 80V. Turn off after afew minutes. Feel the output tran-sistor case. Replace the flybacktransformer if the transistor caseis warm. Sometimes these flybackswill make odd sounds or squeal,and yet the sounds do not indicatea bad flyback. However, internalarcing, or signs of smoke from theplastic case, or arcing around thefocus wire connecting to the focus -screen assembly - any of these in-dicate the flyback is bad.

With the horizontal -output tran-sistor's collector voltage limited to+ 80V, you may investigate ex-cessive flyback and HV voltages,or excessive current caused by aflyback defect, without danger ofdamage to the components.

But first the horizontal systemoperation should be verified, (Fig-ure 4). Scope the Q412 base. Thehorizontal -oscillator and horizontal -driver are operating normally ifyou measure 9V. Next, monitorthe 450V to 500V pulses at the col-lector (case) of Q412. Any smallerpulses between the 15,734Hz pulsesmight indicate a shorted flyback,or an excessive load on one flybackwinding. Noise from arcing HVdiodes might be visible on thescreen; if so, replace the flyback.Other distortion of the pulsesmight mean the flyback's iron coreis cracked; replace it to find out. Ifthe output pulse waveform is cleanand correct, you may assume thecomponents of the horizontal -output stage are normal.


ARM YOURSELFAGAINST STATIC WITHNTE'S NEW PATENTED

FIELD SERVICE KIT.Slat c e lectricty is a real hazard to sensdtive electronicequipment. Now you can protect valuable components inthe field and in the plant with NTE's new Field Service Kit.Our Kit includes everything you need to keep yourequipment free of static -a 24" x 24" table top work mat,waist snap with 8' coil cord, 15' clip -or groundir! line andanti -static component storage bags. Both the wrist strapcord and grounding cord corrain integral current 'imitingresistors.

Unlike other k is currently on the market, NTE'spatented' three -layer const-uctionproduces controlled static drain,

elm nating the darger of sparking and the chance ofadditional component failure during the repair operation.The static -d ssipat.ve, vinyl work surface is durable andits bright green color enhances visibility. The entire Kitfolds down into a compact unit and comes with its ownzip -close bag.Look for NTE's new Field Service Kit and our other staticcontrol products - including our anti -static loam, for

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NTE distributor.Patent issued November 8, 1983.U.S. Patent No. 4,414,260,

NTE ELECTRONICS, INC44 FARRANLI STREET BLOOMFIE'_D, NEW JERSEY 07003

CIRCLE 27t ON FREE INFORMATION CAROCircle (6) on Rep y Card

0411HORIZ DRIVE +79V

tr.

R4284300

SW

R429

+193V

0.68

C4260.01 R430

15 940233

C414

CHECK WAVEFORM

0412HORIZ OUTPUT

+120VREG

7402FLYBACK

TROUBLESHOOTING THE OUTPUT

Figure 4. Check the Q412 base -to -emitter waveform to verify correct operation of theoscillator and driver stages, then analyze the collector pulses to determine whetherthe flyback and sweep circuit is loading down the collector signal.

Using a solder -wick and an adequately hot soldering iron, remove all excess solderfrom the output transformer eyelets when removing the flyback. After replacing theflyback and soldering the eyelets carefully, check between the wiring and thetransformer to be certain there are no open circuits.

Shutdown can be caused by com-ponents of scan -rectified powersupplies, or by defective com-ponents connected to those sup-plies. In Figure 5, check rectifierCR111, regulator Q302 and zenerCR302 of the + 11.24V source.Also, a leaky CR112 diode in theboost -voltage source can causeshutdown. Disconnect one diode ata time and notice the change ofwaveform at the Q412 collector. Aleaky or shorted flyback trans-former loads down the horizontalcircuit and lowers the flybacksignal voltages as well as reducingthe do voltages rectified fromthose signals.

Incorrect labelAn improperly labeled flyback

transformer in the early produc-tion CTC109 chassis can causetrouble during replacement. Theincorrect label has a 146486 RCAstock number on it, and it was in-tended for the RCA CTC108 chas-sis because it produces only26.2kV, which is adequate for a19 -inch set.

The correct label for the CTC109chassis has a 146487 RCA stocknumber, having a 28.6kV ratingfor 25 -inch color receivers. The146487 was superseded by a153175 number, and finally chang-ed to the 154494. With the 154494,the HV lead is supplied.

Removing a defective flybackAfter a flyback is determined to

be defective, its connecting lugsmust have all excessive solderremoved by braided wick and asoldering iron. Rotate the hot ironand wick around the eyelet to suckup the melted solder. Gently try tomove each terminal lug to deter-mine if the lug finally is unstuckfrom the eyelet.

Installing a new flybackBefore mounting the new

transformer, use the iron andsolder wick to remove any excesssolder from the eyelet on thechassis's top side (see photo, lowerleft). While the flyback is removed,replace output transistor Q412, ifdefective. You easily can get to thetransistor and solder all connec-ting wires, including the damperdiode.

Make certain all transformer


If you can't fix your boardwith the enhanced 9000 Series,

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Finally there's a way to conquer some

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that operate independently of the micro-processor bus cycle.

Begin testing boards with the 9000

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kernel-Bus, ROM, RAM and I/O.For testing beyond the bus, Fluke's

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event counting. These three vital trouble-

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DMA Controllers Disk Controllers Video Controllers Video -Generation Circuits

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Not only does the 9000 Series test

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Call Fluke toll -free 1-800-426-0361 or

contact your local representative, and put

your most challenging board to the 9000

Series test. If it can't be fixed with theenhanced 9000, it's probably beyond repair.

FLUKECircle (7) on Reply Card

IN THE U.E. ANO NON.EUROPEAN COUNTRIES. Jaen: wxe Mfg. Co.. Inc.. P.O. Box C9090. MIS 250C. Evereo. WA 98206. Sales:1206) 356-5400. Other. 1206) 397-8100.EUROPEAN HEADQUARTERS: Fluke (Holland) B . P.O. Box 2269. 5600 CG Eindhoven, The Netherlands. (0901958095. TLX 51896.

Copyright 1985 John Fluke MI9. Co.. Inc All n9hts reserved. Ad No 1003-9020

PART OF T402FLYBACK

LEAKY

R1254. 7

CR112

LEAKY

C11.30NF

CR111 C115330NF

+193VSOURCE

+26.7V

SOURCE

10 SOME SHUTDOWN CAUSES

Figure 5. When the pulses at the horizontal -output transistor's collector have smallerdistorted pulses between them (during tests with low voltage),check CR112 andCR111 for shorts or leakage.

+10.53V

U701 146858

LUM I NANCE-CHROMA

26

C71010. 001=

R71422K

+10.53V

R716270

+10. 24V[+6. 34 V)

CR705

R7138200

R4707CONTRAST5000

NO BRIGHTNESS CONTROL

TO

NORMAL -SERVICESWITCH

Figure 6. An analysis of the dc voltages at the U701 pins will solve most of thebrightness problems.

terminals are straight beforemounting the transformer. Solderboth filament leads to thetransformer side lugs. Dress downthe brown -colored filament wirebetween the ferrite core and theframe. If this procedure isn'tfollowed exactly, the CRT filamentvoltage will be excessive, and thepicture tube might be damaged.

Apply solder to the eyelet andtransformer terminal, filling upthe hole with solder. Clean off ex-cess solder and rosin from thesoldered terminals using a metalbrush. Now check the low -rangeresistance of each terminal con-nection to the nearest correspond-ing wiring component. Eachshould test virtually zero. Con-tinue to resolder the transformerterminals until a low resistancereading is obtained for all.

Excessive brightness,then shutdown

A bright raster that graduallybecame brighter before shutdownstopped the receiver operationwas the symptom. When adjust-ment of the brightness and screencontrols accomplish nothing,measure the do voltages at eachpin of IC U701. When a pin with anincorrect voltage is found, usesolder wick to remove the solderfrom around that pin until the pinfinally is not connected to the wir-ing. Then measure the resistanceto ground. Commonly, such leak-ages are about 1,0002 or less. Forall low readings, replace the leakyU701 (146858).

In another CTC109 chassis, theexcessive brightness could not becontrolled, resulting in shutdown.This was caused by the picturetube. Check for that by unpluggingthe picture tube socket and oper-ating the set to determine if shut-down occurs. It should not.

High brightnesswith retrace lines

A leaky luminance/chrominanceU701 IC can produce excessivebrightness with or without retracelines. The retrace lines often canbe seen with the screen controlturned completely down. Ac-curately measure do voltage andresistance -to -ground of all IC pins(Figure 6). A lower -than -normal de


voltage indicates internal leakageor external leakage through adiscrete component.

The 5701 service switch cancause high -brightness problems,even when the switch contacts testgood on a meter. Replacement ofthe switch is the only certain cure.

No brightness controlSuspect leakage in luminance/ -

color IC U701 when the brightnesscontrol can't be turned down.First, collapse the sweep with theservice switch and notice if allthree colors seem to be on thescreen. Turn up the screen controluntil all three can be seen. Checkall grid, cathode and screenvoltages of the picture tube afterthe sweep has been restored. If araster is produced by the highersetting of the screen control, go tothe luminance circuit and U701,(see photo at right).

One remote control model hadno control over brightness, and pin26 of U701 measured only + 4.1V(it should be + 10.24 as shown inFigure 6). When pin 26 was unsol-dered from the board, it measured76811 to chassis ground. Afterreplacement of U701 with a146858, the resistance from pin 26to chassis ground was 7.1k(á. Werecommend that resistance testsbe added to the usual voltage testof integrated circuits. The new ICrepaired the problem.

Another CTC109 with similarsymptoms and measurements wasnot helped by replacement ofU701, which had a low voltage atpin 26. Finally diode CR705 wasfound to have a 2,000iá short.Replacement of CR705 broughtgood operation.

Intermittent brightnessIntermittent brightness can be

caused by either the luminance orthe picture -tube circuits. Carefullymonitor all voltages of the lumi-nance U701, and the picture -tubesocket. Check for a defective pic-ture tube. R9 (22k) and Cl (0.01)on the CRT -socket board (see Fig-ure 7) have caused many intermit-tent raster problems. Alwayscheck these at the beginning oftests.

With another CTC109 chassis,the brightness would go up and

The IC near the center of the photograph is U701 the luminance/chrominance in-tegrated circuit. Measure the dc voltage and the resistance of all IC pins to groundand compare the readings with the Photofact. Critical for brightness levels is thevoltage at pin 26. Also, remember to measure the + 10.53V supply that powers U701before condemning the integrated circuit.

down quickly, sometimes stayinglow for some time. A dc -voltagemeasurement of CRT pin 7 indi-cated a constant change of voltage(Figure 7). Since this is the com-mon screen grid, it would accountfor the brightness variation. R9and Cl were tested thoroughly butboth were perfect. Therefore, theentire screen -and -focus -controlassembly was replaced, and thatstopped all the unwanted bright-ness changes.

C705 (120pF at anode of Q701phase compensation) might be-come leaky and cause the raster todarken. The picture becomes total-ly dark, if L807 (near Q801, theburst clamp/keyer) opens. An in-termittent DL701 delay line willproduce intermittent brightnessand pictures.

Poor focusIf the focus control can supply

focus voltage above and below thenominal 7kV rating, and if thefocus adjustment brings a bettersharpness of scanning lines withplenty of adjustment available onboth sides (but the focus, andperhaps the brightness, is just

below average) suspect the picturetube.

Verify the diagnosis by a picture -tube tester, or by operating thereceiver from a picture -tube testjig, if you have one.

Erratic focus can be caused inthis model by a defective focuscontrol, which is part of the focus -and -screen -control assembly(Figure 7). Arc lines in the rastercan be caused by the sameassembly, which must be replacedas a unit.

An unusual pictureA very unusual problem can oc-

cur in CTC109 chassis when C105,the only rectified -line -voltagefilter capacitor, is open. It has anappearance like an outdoor waterfountain with its water overflow-ing into a similar basin below.An actual picture of the effectis shown on page 18, whichshows color bars in black -and -white. When another 600µFcapacitor was paralleled withC105, the performance becamenormal. Use an original partnumber capacitor for replacement.

In remote -control GER models,


THE MARK III

HV CIRCUIT SCANNER* Checks the horiz output circuit for open / shorts,* Checks the flyback, yoke, PC, and HV mult,* Checks all scan derived B + sources,* Checks all circuits that rely on scan derived B+ voltage,* Checks for open safety capacitor,* Checks the emitter circuit of the horiz output,

THEN,

* Provided the green normal light is lit, the Mark III will safely powerup the TV set so that you can "look" for open circuits by examiningthe picture on the CRT.

* Circumvents all start up and horiz drive related shut down circuits.

APPLICATIONS: The Mark Ill will analyze the horiz, flyback, hi -voltage, scan derived B + sources, yoke, pin cushion, HV multiplier cir-cuits in any TV set that employs either an NPN transistor or a singleSCR for its horiz output device. This applies to any age, any model, anychassis, any brand - - - including Sony.

In brief, the "test" function scans for shorts, the "run" functionpermits you to observe any "open" circuits via the symptoms that ap-pear in the CRT screen.

HOOK UP: Simply remove the set's horiz output device and replaceit with the scanner's interface plug. No wires to disconnect, no otherconnections required (not even a ground connection).

MISTAKE PROOF: No damage will result if an error is made duringhook up. The scanner simply won't turn on until the error is corrected.

PUSH THE TEST BUTTON Just one of the four lights will lite.

RED OPEN LIGHT means the emitter circuit of the horiz output stageis open (no ground path).

YELLOW SHORT LIGHT means the flyback primary, HV multiplier,vertical output, horiz driver, and R -B -G color output stages are notshorted. Instead, a circuit that normally draws a small amount of cur-rent is shorted (i.e. the tuner, IF, AGC, video chroma, matrix, vertical orhoriz oscillator).

RED SHORT LIGHT means either the flyback, the HV multiplier, thevertical output, horiz driver or one of the RBG output transistors isshorted.

GREEN NORMAL LIGHT means the TV set's entire flyback circuit istotally free of shorts. It also means that it is safe to power up the TV setwith the "run" button so that you can look for open circuits by observ-ing the symptoms on the CRT screen.

FEATURES: All start up circuits and all horiz drive related shut downcircuits are automatically circumvented by the Mark Ill during all testand run functions. During the test function all flyback secondary outputis limited to approx 80% of normal. 2nd anode voltage is limited to ap-prox 5 KV.

This means all circuits that are not shorted will have some 80% of theirnormal B + voltage during the "test" phase, It also means that anyshorted circuit will have zero DC volts on it. This feature makes anyshort easy to isolate.

The MARK Ill sells for only $59500The money you are now spending for unnecessaryflybacks alone will easily pay for your Mark Ill. Whynot order yours today!

Visa and Mastercharge Welcome !

Diehl Engineering 6661 Canyon Drive "F" Amarillo, TX 79110Phone: (806) 359-0329 or (806) 359-1824


E

&

r

AG

JAN

low many times have you saidIf I could only get this TV

to power up, without burning up,- I could fix it !!

Well, the Mark Ill will let you do just that.The test button checks the entire scan circuit for shorts.The run button checks the entire TV set for opens.

If you act now, this certificate will entitle you to a $10000 discount on the all newMark Ill, making the total price only $49500 plus freight.

(See the reverse side of this card for details)

OFFER VOID JAN. 31, 1986 ONE DISCOUNT CERTIFICATE PER SALE

CUT ALONG DQTTUI4241 t D_V_SF`AS NI ORDLELFORM

;200

TWO HUNDRED DOLLAR CERTIFICATE

How many times have you said.

"Once I get a start up / shut downproblem isolated down to circuit level,

- it's as good as fixed !

The fact is, all start up/shut down problems ultimately show up as a dead set symptom that does notrelate to the actual defective circuit, start up and shut down problems are invariably caused byeither a start up, H. drive, B + "run" circuit, safety capacitor, H. yoke, pin cushion, flyback. HVmultiplier, shorted scan derived B + or, by a defective shut down circuit.The Mark V makes the entire job of isolation easy. It puts you right where you want to be - - - in mereseconds, by automatically checking each individual portion of the overall circuit on it's own merits.If you act now, this certificate will entitle you to a $20000 discount on the all new Mark V analyst.Making the total price only $7950° plus shipping.

(See reverse side of this card for details)

DISCOUNT CERTIFICATE

200

2 0OFFER VOID JAN. 31, 1986 ONE DISCOUNT CERTIFICATE PER SALE

CU' AILING DUI t.D L.NL AND USE AS AN UHDLH FORM

E Please Have A Salesman Call On Me ..S

&

I am not concerned about getting a discount on my test equipment.However, if you will send a representative to my shop to give me a "hands on" demonstration, I agree to

M pay the regular retail price, as long as it will do everything that has been stated. And, as long as the unit isA as easy to operate as stated in this ad.'G We're growing- Having recently moved into our brand new 10,000 sq. ft. facility, we are now hiring

technicians, tech writers, semi -technical production workers, regional and local sales representatives,and service oriented engineers. If you're interested, send your resume to: DIEHL, 6661 Canyon Drive

A Building "F", Amarillo, Texas 79110, (806) 353-5768.N

Your Name Street

City

AC ( )

State

Phone # Signature

Mark III Order FormEnclosed is my check for $49500 along with this $100°° discount certificate. payment infull for my Mark Ill HV circuit scanner. Please ship as soon as possible via UPS BlueLabel (Diehl pays freight).

C Please ship my Mark III to me C.O.D. upon arrival I agree to pay 49500 plus freight.

Charge $4950° to my Visa card Mastercharge cardMy card # isMy card expires Phone orders welcome on charge card orders.

PLEASE PRINT

Name Street address

City

AC ( )

State Zip

Phone # Your signature

Mail to Diehl Engineering 6661 Canyon Dr. "F" Amarillo, TX 79110

Mark V Order FormEnclosed is my check for $7950° along with this $200°° discount certificate. payment infull for my Mark Five circuit analyst. Please ship as soon as possible via UPS BlueLabel (Diehl pays freight).

Please ship my Mark V to me C.O.D. upon arrival I agree to pay 7950° plus freight.

Charge $7950° to my Visa card Mastercharge cardMy card # isMy card expires Phone orders welcome on charge card orders.

PLEASE PRINT

Name Street address

City State Zip

AC( )

Phone # Your signatureMail to Diehl Engineering 6661 Canyon Dr. "F" Amarillo, TX 79110

Business Reply CardFIRST CLASS PERMIT NO. 262 Amarillo, TX

POSTAGE WILL BE PAID BY ADDRESSEE

Diehl Publications6661 Canyon Drive Bldg EAmarillo. Texas 79110-9990

NO POSTAGENECESSARYIF MAILED

IN THEUNITED STATES

* Checks the horiz output stage for opens / shorts,* Checks flyback, yoke, PC, and HV mult,* Checks all scan derived B + sources,* Checks for open safety capacitors* Checks for open ground path for horiz output stage* Checks for open primary LV supply,* Checks for error in interface connections,* Checks for proper LV regulation,* Checks for proper start up circuit operation,* Checks for shorted horiz driver transistor,* Checks the operation of the horiz osc / driver circuits,* Checks B + "run" supply for the horiz osc / driver circuits,* Checks all circuits in the TV set that rely on scan derived B* Automatically circumvents all start up circuits and horiz drive

related shut down circuits.

HOOK UP: (Identical to Mark Ill)

OPERATION: Turn the Mark V on, turn the TV set on, then, simply lookat the lights.

RED "HOOK UP" LIGHT means that you have made an error in hookup. No damage has been done, correct the problem then continue.RED "EMITTER" LIGHT means that the ground path for horiz outputstage is open. Correct the problem then continue.

RED "B + OPEN" LIGHT means that the primary LV supply in the TVset is open. Correct the problem then continue.No "top row lights" equals normal.

Look at the middle row of lightsRED "START UP" LIGHT means that the start up circuit in the TV setis not working (no start up pulse).

GREEN "START UP" LIGHT means the start up circuit in the TV set isworking normally. Yes, it is 100% accurate. Even on Zenith's singlepulse start up circuit !

RED "HORIZ DRIVE" LIGHT with a green start up light means thatthe horiz driver transistor in the TV is shorted (E to C).

GREEN HORIZ DRIVE LIGHT means that the horiz oscillator anddriver circuits are operational.

READ THE DC VOLTAGE METER THEN,

PUSH THE TEST BUTTONIf the meter comes up to, or, falls back to, factory specified DC collec-tor voltage, the LV regulator circuit is working. If it fails to do so, it is notworking!

RED "B+ RUN" LIGHT means that the B+ source that normallykeeps the horiz osc / driver circuits running after the start up B + pulsehas been consumed has become open.

GREEN "B+ RUN" LIGHT means that the B+ resupply voltage(scan derived) is being provided. All is normal if all three lights are nowgreen.

The scan circuit short detector in the Mark V is identical in all ways tothat which is used in the Mark Ill. Operation is also identical. Both unitsare virtually indestructable when simple directions are followed. Bothunits carry a full year's warranty against defects in materials andworkmanship (parts and labor). Either unit can be easily repaired byalmost any technician in his own shop.

If the green "circuits clear" light Is now lit

It is now safe to push the "run" button and examine the symptoms thatappear on the CRT screen, for the purpose of isolating any "open" cir-cuits.

Except for hook up and CRT filament warm up time, this test can easilybe completed in two to five seconds!

The Mark V sells for only $99500

Stop losing money on start up / shut down scanderived B+ problems; order your Mark V today!

Visa and Mastercharge Welcome !Diehl Engineering 6661 Canyon Drive "F" Amarillo, TX 79110

Phone (806) 359-0329, or (806) 359-1824


REPLACEN

R1SD1.6M

TEST

R9

7

-iSPARK

R1 SC

39Mvw

GAPR' SF

m

GRNBLUE

RED

R7 SE

9.9M

R I

FOCUS15.M i

J

SCREEN AND FOCUS ASSEMBLY

RSCREEN7.2M

GRAY WIRE WH-GN

TO COLD END OF HV WINDING WIRE FROM FLYBACK WITH 9KV

BRIGHTNESS PROBLEMS

Figure 7. Most components shown can cause problems with screen brightness because of the voltage -divider type of circuit.

When filter C105 was open in the CTC109, the picture had full width only twice perraster because the filtering was virtually zero. Because the hum has a 120Hz frequen-cy, narrow parts of the picture move slowly upward, color bars do not move.

suspect a defective C105 when theTV chassis will come on but youcannot switch it off.

One vital waveformIf the symptoms are no picture,

no dial light, normal sound, andnormal high voltage, check byscope for 60Vp-p negative -goinghorizontal pulses at pin 5 of the FStuner control module. The sche-matic says - 60V pulse, whichmight deceive the unwary intomeasuring with a dc meter; thiswill not work. The signal consistsof pulses.

Check for an open L103 that isconnected to the flyback's pin 7. IfL103 is not open, check for erraticsoldered connections on L103. Ifnot open there, go on tracing untilthe open or short is found. Thepulses must be restored to pin 5 onthe control module.


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Introduction tomicrocomputer troubleshooting

Fundamental disk- drivetroubleshooting

By Bud Izen CET/CSM

From the workbenchI'm a consumer electronics

analog technician from 'wayback. The computer caught upwith me when I discoveredthat a word processor helpedme to prepare magazine ar-ticles and lessons for elec-tronics courses I wasteaching. I was on-line at last!Or, I was until my one -and -only disk drive broke down inwarranty.

I discovered that I had todrive 30 miles to the nearestwarranty station, and waittwo weeks; not for the part,but for the warranty repairto be authorized by the fac-tory. Then, when the unit

finally was returned, it had asubstitute part in the powersupply that had been sloppilyinstalled by the technician.

The same symptom reoc-curred about a month afterthe unit went out of warran-ty. I knew absolutely nothingabout disk drives at thattime, other than how to in-sert and remove the disks,how to connect the drive tothe interface card and how toplug it into the correct slot in-side the computer. But on theother hand, I did not want todrive 30 miles each way andwait another two weeks. So Itold myself the same thing

that I have told countlessother students and techni-cians: If you can diagnose atelevision, you can diagnosealmost any electronic prod-uct. I took a deepbreath andremoved the ur screwsholding the case to the drive.

Braving the unknownMy first thought was,

"What does this thing do nor-mally?" It takes the informa-tion from the computer andstores it on the disk, or ittakes information off the diskand loads it into the com-puter. Pretty simple, so far.Now, what are the failuresymptoms? When I turn theunit on, the in -use LEDcomes on and the disk spinsaround, but it doesn't loadanything into the computer.

Normally, this is a seriousproblem because all the pro-grams that can be loaded intothe computer to have it checkitself out are on the disk. Youneed the diagnostic disk todiagnose, but the mechanismyou want to diagnose won'tlet you load the diagnosticprograms. This vicious circleconsiderably complicates theservicing procedure.

My first step was to turnthe disk drive off (by pressing

Photo courtesy Apple Computer, Inc.

system reset), and takevoltage readings on all thepins of the ICs on the boardmounted onto the drive. Thisensures that all the powersupply voltages are normal.Then, because the circuitsare digital, I expectedspecific voltages to changewith varying input condi-tions. I wrote down thevoltages because there wereso many of them. Having lit-tle regard for the nuances ofdigital, I used a $9.95 RadioShack analog (yes, analog)meter.

Then I put a disk that Iknew had good informationon it into the drive, shut thedoor on the drive, and gavethe keyboard command (PR#6)to turn on the drive. Onceagain the LED came on andthe disk -drive motor came onbut the program did not load.I wrote down the dynamicvoltage measurements next tothe static ones, then turnedthe unit off

Next, I referred to the sche-


matics of the disk drive inter-face card mounted inside thecomputer, and analog cardthat mounts on top of thedrive. This was what I need-ed. Not every voltage waslisted, because some of thelines were obviously designedto carry information thatwould vary between the TTLlevels of zero and +5.

After examining the sche-matic and comparing myreadings, it was apparentthat some of the voltages onone particular IC did notchange, yet should have. So, Icalled up a computer partsvendor and ordered two ofevery standard IC and tran-sistor used on either diskdrive board. My entire ordercame to less than $20.00.

Three days later, thepackage of parts arrived inthe mail. I removed the one ICI needed and plugged it in. Itworked. About a year later,the same symptom occurred,and I followed the same pro-cedure again, using the samefancy test equipment. Thistime it appeared that thevoltages on two ICs were notchanging. It turned out to bethe same IC as before, plusone other. This time therepair took five minutes from

start to finish, instead of anhour plus three days ofwaiting. The most -time-con-suming part of the job wasremoving and replacing thecase. The second repair wasas successful as the first.

Timing is everythingAbout six months later, my

word processor programstarted acting up. Every sooften, it would not save a filecorrectly. In order to treat thesymptom, I began to back upmy work on two separatedisks at the same time. Theproblem kept getting worse.Sometimes neither backupcopy was any good.

About that time, I remem-bered reading an article inone of my user -group maga-zines about problems relatingto disk timing and how if therotational speed of the disk(about 300Hz) varied too muchor became erratic that datacould be lost or become other-wise unreadable. This sound-ed like my problem. So I pur-chased another diagnosticdisk from the user group andfound out that was exactlywhat was wrong. All I had todo was to run the diagnosticprogram while observing theprint-out on the monitor, and

adjust a small pot on the mo-tor power supply and speedcontrol board at the rear ofthe disk drive. About twomonths later, however, thedisk drive completely ceasedfunctioning. I called up Ap-ple, and the technician therewas helpful. I explained allthat I had done (everythinglisted above) and that nothingseemed wrong. He suggestedthat I take the unit to anauthorized service stationand have it diagnosed. Hethought it was a head prob-lem. The service station endedup replacing the entire me-chanical assembly, afterwhich the drive worked fineand still does today.

Here's one other tip that ap-plies to every card -edge con-nector in a computer or anyother electronic device. Cleanthe edge connectors with apencil eraser once in a whileto keep excess corrosion andoxidation from causing openconnections, intermittent orerratic operation.

Working on computers andcomputer peripherals is nothard. In fact, as you see frommy experiences, if you al-ready are a competent techni-cian, you should have fewproblems.


Peripheral connections

An asterisk (*) following the mnemonic name of the line in-dicates that it is a negative logic line. In other words, the lineis active (logically high) if a low voltage (about OV) is placedon it, and inactive (logically low) when about +5V is placedon it.

Pints Description.

01 I/O select'; There are 256 addresses set up for each ofthe seven slots. If the processor is addressing a particularslot, this pin (on the slot being addressed ony) will be pulled,ow. It is able to drive four TTL loads (fanout of four).02 The Apple uses a 16 -bit address system. The addressines are asserted by the 6502 microprocessor within 300ns

of the start of PHI 1 (the complement of the PHI 0 systemmaster clock).330435060708091011

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18 RAN; this is the read/write line asserted by the 6502.When the line is high, a read cycle is in progress. If low, awrite cycle is in progress. This line has a fanout of 16.19 NO CONNECTION20 I/O STROBE'; When PHI 0 is high, this pin will go low onall slots if the 6502 is addressing an I/O device whose ad-dress is hex C800 to CFFF. Fanout of four.21 RDY; this is the ready line to the 6502. Designed tochange only when PHI 1 is high, if this line is brought low, themicroprocessor will enter the halt state upon the next readcycle. This line should be asserted using tri-state logic.22 DMA'; The direct memory access control line, whichshould be asserted using tri-state logic.23 INT OUT; This interrupt line is daisy chained through theperipheral slots, and is assigned to low priority devices.Fanout of four.24 DMA OUT; this line is another daisy chain line for directmemory access to lower priority devices. Fanout of four.25 + 5V26 GND27 DMA IN; this is the direct memory access daisy chainline from higher priority devices. This line looks like no more

than four TTL loads to the driving device.28 INT IN; this is the interrupt daisy chain input line fromhigher priority devices. Looks like no more than four TTLloads to the driving device.29 NMI*; this is the non-maskable interrupt line to the 6502.It is active when a low voltage is applied, and should beasserted using tri-state logic.30 IRQ'; this is the interrupt request line to the 6502. It isactive when a low voltage is applied, and should be assertedusing tri-state logic.31 RES.; this is the system reset line. It is brought low bypressing the reset button on the keyboard. It is designed todrive two MOS loads per slot.32 INH"; this is the inhibit line. If a device brings this lineactive (low), all ROMs will be disabled (Hex addresses D000through FFFF). This line should be asserted with tri-statelogic.33 - 12V34 -5V35 NO CONNECTION36 7M; this is a 7MHz clock that can be used to drive up to16 TTL loads.37 Q3; this is a 1MHz signal that can be used for generaltiming purposes and can also support up to 16 TTL loads.38 PHI 1; the complement of the PHI O system master clock.This line can drive up to 16 TTL loads,39 USER 1; a user -defined line that must be hard -wired bymeans of an on -board jumper.40 PHI 0; the system master clock capable of driving 16 TTLloads.41 DEVICE SELECT'; the Apple system sets aside 16 ad-dresses for each slot. If the processor reads or writes to oneof these addresses, the signal on pin 41 of that particular slotwill be brought low when PHI 1 is true. Fanout of four.42 D7; lines D0 -D7 represent the 8 -bit system data lines.The 6502 asserts a write cycle no less :han 300ns after PHI 1is true, and expects the data to be asserted and stable noless than 100ns before PHI 1 is false. These lines can supportup to eight low -power Schottky TTL loads.43 D644 D545 D446 D347 D248 D149 DO

50 + 12V

Table 1. The Apple uses its own non-standard 50 -connector bus system for peripheral and expansion purposes. This tabledescribes the ft:nction of each pin on the bus.


In most microcomputer systems,if the disk drive fails, you're out ofbusiness. Ordinarily, microcom-puter users store all of their pro-grams and data on floppy disksand if the drive won't work, there'sno way to load programs or data.Fortunately, a competent techni-cian, armed with the correct tools,test equipment and information,should have no problem restoringa failed disk drive to operation.Even if all your servicing ex-perience is on analog equipmentand you've never worked on com-puter equipment. The informationthat follows applies specifically totroubleshooting an Apple diskdrive, but the procedure, withmodification, is pertinent to thedisk drives of most personal com-puters.

Disk drive specificsBesides the drive mechanism,

there are three main modulesassociated with the Apple diskdrive system: the interface cardthat plugs into an expansion slot,the analog board that sits on top ofthe drive mechanism, and themotor control board located at therear of the drive. The drive re-quires three power supplies: + 5V,+ 12V and - 12V. The + 12V isused to run the motor; all three ofthe supplies are used on the inter-face and analog boards for variouspurposes.

The Apple uses its own non-stan-dard bus system for peripheral andexpansion purposes. This is a50 -connector bus. As you view theinside of the Apple from thekeyboard, pins 1 to 25 are on theright (component) side of the bus,while pins 26 to 50 are on the left(foil) side. Pin 1 is the right -sidepin closest to the keyboard; pin 50is opposite pin 1. Table 1 describeswhat each of these pins does.

A thorough examination ofTable 1 should give you a basicunderstanding of what is happen-ing on the slot -connector lines.Here's how the disk drive systemtakes advantage of the lines.Because the disk drive is strictly aslave device, meaning it cannotcause interrupts or take over con-trol of the Apple from the 6502, ithas no need for many of the lines.Therefore, it does not need the in-formation on lines 18, 20, 21, 22,29, 30, 32, 36, 38, 39 and 40. Alsobecause it needs only an 8 -bit ad-

dress, it does not use lines 10 to 17.Line 27, DMA in, is looped throughto line 24, DMA out. Line 28, INTin, is likewise looped through toline 23, INT out. None of thoselines are used by the disk system.

There are several ICs located onthe interface board that interpretthe signals on the bus so that diskread -and -write operations cantake place at the correct time.Likewise, the signals going to andfrom the analog card are condi-tioned. The interface card andanalog card communicate with

each other over a 20 -wire connec-tor bus. This bus is described inTable 2, page 27.

Tracking downdisk drive problems

Referring to Table 2: It shouldnow be a fairly straightforwardprocedure to trace disk drive prob-lems by using any of your favoritepieces of test equipment. General-ly speaking, a logic probe is mostuseful to get you in the ballpark. Ifyou are really in doubt as towhether or not a pulse train is

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4300 West 62nd StreetIndianapolis, IN 46268

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really there, the oscilloscope isyour best bet for making a deter-mination. Otherwise, you can use astandard voltmeter to track downa great majority of failures. Forexample, let's see what should hap-pen if the system is writing someinformation to disk 1.

Starting with the information onthe bus itself, the disk drive isselected via data on the addresslines, and the device enable line isbrought low. The I/O select linealso goes low. The data then can befed over the bus to the interfacecard. From there, it is sent to theanalog card as follows:

The disk addressing informationis sent over lines PHI 0 throughPHI 3. The drive enable 1 line goes

The disk interface board, which plugs in-to the computer, contains all of the cir-cuitry necessary to effect communica-tions between the computer and the diskdrive. The use of ICs make a complex cir-cuit appear relatively simple.

low. The write protect line stayslow. The read data line is inactive.Data is fed to the disk over thewrite data line. The write requestline goes low. All the power supplylines should be enabled. The motorshould come on, and the in -useLED should light.

The disk read process is similar.Starting at the bus, the device isselected as above, while the 6502prepares itself to receive data. Theinterface card then can ready itselffor data input by enabling the

following lines on the analog card.Lines PHI 0 through PHI 3 assertthe disk -addressing information.The drive enable 1 line goes low.The read data line receives infor-mation off the disk and sends it tothe interface card, which puts it onthe data lines. The write data lineis inactive. The write request linegoes high. All the power supplylines are enabled. The motorshould come on, and the in -useLED should light.

If the read -or -write operation

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How many of these questionscan you answer ?

(1) Every circuit has a beginning and an ending. Where does thiscircuit begin?

(2) Specifically, what is the purpose of this circuit ?(3) What turns it on ? What turns it off, or does it ever really turn off ?(4) Does this circuit have a shut down feature ? If so, which com-

ponents are involved ?(5) What would happen if 0103 were to become shorted E to C ?(6) What purpose does Z115 serve ?(7) What would happen if D114 became shorted ?(8) What purpose does C126 serve? What will happen if C126

becomes open ?(9) Is the winding between terminals 3 and 4 of the flyback a primary

or a secondary winding ?(10) What purpose does C117 serve ? Exactly what does it do, and

exactly how does it do it ?(11) Exactly what do resistors R113, 114, 115, 116, and 117 do ?

What happens if they change value ?(12) What occurs that causes this circuit to produce an initial start up

pulse ?

(13) Why does this entire circuit become shorted and begin to destroyhoriz output transistors if the regulator SCR becomes shorted ?

(14) There is exactly one safe and practical method of circumventingthis LV regulator circuit for test purposes. This technique doesnot involve a variac. Instead, you must disconnect one wire thenconnect a jumper wire from terminal #4 directly toWhich wire do you disconnect and where do you connect theother end of your jumper wire?

(15) If SCR100 is shorted, this circuit will still "eat" horiz output tran-sistors even if you are using a variac. Why ?

(16) Why does this circuit use a floating ground ?

We publish a monthly magazine called the Technician / Shop OwnersNewsletter. Each month we take a popular circuit and absolutelydiasect it.

Using color coded pictorial schematics such as the one above, we"map out" every action in the overall sequence of events that musttake place during each and every cycle.

Beginning with the very first "action" in the sequence (which justhappens to be depicted in the above schematic) we explain exactlywhat is taking place. We then explain the function of every componentin that portion of the circuit. After explaining the function of each com-ponent, we show you how to troubleshoot that particular "action" orfunction.

After reading our newsletter on this circuit, you could answer all of theabove questions as fast as anyone could ask them. In fact, you willthen know everything there is to know about this circuit. Including howto troubleshoot it ! !

Regardless of whether you work on TV sets, stereos, radios orcomputers, just having the ability to "diasect" an electronic circuit(any circuit) is worth a fortune. In reality, "diasecting" is exactly whatour newsletter is designed to teach you.

Because of the manner in which our newsletter is written, the subjectmatter that is gained from each monthly issue is so extremely broadthat it will "spill over" into your everyday troubleshooting routine, andbe applied to totally unrelated circuits.

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took place under software control(in other words, as part of a pro-gram), then after a successfuloperation the software should con-tinue to execute normally. Displayof the dreaded screen message I/OERROR means that something didgo wrong. Well -designed pro-grams should have built-in errorhandling routines to avoid dataloss or program failure in suchcases. However, it is difficult towrite a program that will accountfor all possible types of errors,either machine- or user -generated.

If you were trying to load a pro-gram or save one to disk and ifsomething goes wrong, you willsee the same error message - I/0ERROR. The only exception tothis is when a bad, but otherwisecomplete, write -to -disk has occur-red. The information was suc-cessfully placed on the disk, but itmay have been stored in the formof garbage because of many fac-

This analog board is located inside thedisk drive housing.

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tors. Some of these include a hard-ware defect somewhere in thesystem (the least likely possibility),a bad disk, or a disk speed prob-lem. You will find out about badsaves the next time you try to loadthat information back into themachine for use. Either you willget an I/O ERROR or the load willwork, but you will only get gar-bage on the screen when the pro-gram runs.

To eliminate the possibilities, tryloading a known -good piece ofsoftware that was made on

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another machine. If it works, youknow that the disk speed is withintolerance, and that the completesystem is capable of doing a read -from -disk operation. Next, get adisk that you know is good andplace it in the drive. Load the pro-gram in memory onto the disk.Then type in the commandVERIFY from the keyboard. If theBASIC cursor prompt comes back,then the information was loadedwithout error. Now, load that pro-gram right back into memory. If itloads correctly, the only problem

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you have relates to the first diskitself. If the program gives an er-ror on load or appears to be gar-bage when listed or bombs whenrun, it is likely that there is a disk -write operation. Check the diskspeed first, just in case. Then gothrough the hardware checkslisted above. If you are careful andobservant, and follow the pro-cedures explained above, youshould have little difficulty track-ing down a majority of failuresassociated with the disk operatingsystem.

Table 2.

pin# Description01 GROUND02 PHI 0; there are four addressinglines, of which this is the first.03 GROUND04 PHI 105 GROUND06 PHI207 GROUND08 PHI309 - 12V10 WR REQ*; the write -request line,active low.11 Vcc; + 5V12 Vcc: + 5V13 + 12V14 ENBL1*; the interface will sup-port two disk drives. Line 14 is usedto enable whichever drive is desiredunder software control. Drive 1 is thedefault drive, normally used to bootthe operating system. An EXCLUSIVEOR circuit is used, preventing bothdrives from being simultaneouslyenabled. This line is active low.14B ENBL2'; this is also an activelow line, energized when drive two isselected.15 + 12V16 RD DATA'; when this line isbrought low, it enables a data readfrom the disk.17 + 12V18 WR DATA; when this line ismade active, it enables data to bewritten to the disk.19 + 12V20 W PROT; when this line is madeactive, it enables data to be written tothe disk.

Note that lines 1, 3, 5, and 7 are alltied together. Pins 13, 15. 17, and 19likewise represent the same voltagesource sent over four different linesand tied together upon reaching theanalog card. The same is true of pins11 and 12.

Table 2. The interface board and theanalog circuit board communicatewith each other via a 20 -conductorconnector bus. Table 2 describes thefunction of each of the conductors inthe bus.

ConclusionThe most important aspect of

troubleshooting is to take carefulaccount of the failure symptoms,relate them to your knowledge ofhow the system operates, and thendecide which of the basic systembuilding blocks are most likely tobe causing the symptoms. Afterthat, try to develop functionaltests, such as those described inthis article, either to positivelyeliminate those blocks that are notcausing the problem or positivelylocalize the symptom to the block

that is causing the problem. Do notbe in too much of a hurry to startusing test equipment - the mostimportant piece of test equipmentis that wonderful God-given onebetween your ears. The more youuse it, the less time you will needto use anything else. Keep an openmind; do not try to prove correctyour own initial assumptions.Above all, remember that anycomputer system is at best a sim-ple and repetitive one. It is certain-ly nothingto fear.

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Howard W. Sams & Co., Inc.A Subsidiary of Macmillan, Inc.4300 West 62nd StreetIndianapolis, IN 46268

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DM m

Circle (1l) on Reply Card


Testyour electronicknowledge1. Which of the following is trueabout the symbols in Figure A?A.) Both symbols represent thesame device.B.) Both are JFET symbols, butthe one in (b) is not symmetrical.C.) Both devices are used in ClassB amplifiers.D.) The one in (b) represents adevice that has two bases.

Figure A.

2. Which of the following is usedas a very fast switch?A.) VDRB.) LDRC.) tunnel diodeD.) zener diode

3. In which of the followingmight there be a deathnium trap?A.) A microwave transmitterB.) An AM stereo receiverC.) A CD playback systemD.) A transistor

4. The same square wave is beingused to test two differentamplifiers. Assume the same scopesetup for both tests. The leadingedges of the output waveforms areshown in Figure B. Which of thefollowing is correct?A.) The amplifier for (a) has thegreater bandwidth.B.) The amplifier for (b) has thegreater bandwidth.C.) You cannot determine thebandwidth from this test.

5. To transmit and receive withthe same antenna, use aA.) duplexer.B.) diplexer.

6. Which of the following is equalto one femto ampere?A.) 10 24AB.) 102'AC.) 1018AD.) 10-15A

7. For the circuit of Figure C, thepositive lead of the milliammetershould be connected toA.) point x.B.) point y.

8. With no input signal to theclass A amplifier of Figure C, themilliammeter indicates a currentof 120mA. When a pure sine waveis applied to the input terminal, thecurrent (as indicated by themilliammeter) shouldA.) increase.B.) decrease.C.) not change.

INPUT°-)

MILLIAMMETERx

Figure C.Vcc

a

o

9. The pendulums in Figure Dhave the same length and weight,but the one in (a) swings throughan arc that is twice the length ofthe arc in (b).A.) It will take the one in (a) exact-ly twice as long to swing throughits arc.B.) It takes the one in (a) longer toswing through its arc, but it willnot be exactly twice as long.C.) It takes the same amount oftime for the pendulums to swingthrough their arcs.D.) This question cannot beanswered.

Figure D.

10. Which of the following com-ponents might be checked with aringing test?A.) voltage -controlled oscillatorB.) capacitorC.) inductorD.) tristate buffer


Answers are on page 59

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Reprinted by perm

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Copyright 1986, E

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schematics

Schem

atic No.

RC

AV

ideo display monitor

MM

C100 chassis

2077G

EC

olor TV

- PM

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2078

JAN

UA

RY

1986P

roduct safety should be considered when com

ponent re-placem

ent Is made In any area of a receiver. T

he shadedareas of the schem

atic diagram designate the com

po-nents In w

hich safety is of special significance. ItIs

recomm

ended that only exact cataloged parts be used forreplacem

ent of these components.

Use of substitute replacem

ent parts that do not have thesam

e safety characteristics as recomm

ended In factoryservice inform

ation may create shock, fire, excessive

x-radiation or other hazards.

This schem

atic Is for the use of qualified technicians on-ly. T

his Instrument contains no user -serviceable parts.

The other portions of this schem

atic may be found on

other Prof ax pages.

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áffilááálóállááffildExplosive growth predicted for

PC -based instrumentsUses for personal computer -

based instruments are multiplyingso that the world market for theseinstruments will top $1 billion by1990, according to a report fromMarket Intelligence Research ofPalo Alto, CA. Lower prices andhigh performance of PCs will fuelthe market to a 38% average an-nual growth rate between1985-1990.

The fastest growing segment ofthe PC -based instrument marketwill be in test and measurement,according to the report. Althoughthe number of PC -based in-struments is still very small com-pared to the number of non -PC -

based instruments now used, thespread of these instruments isremarkable considering the shorttime (since 1982) that PCs as testinstruments have been on themarket. A transformation of thetest and measurement industry isexpected as a result of widespreadpopularity of the PC -based instru-ment. This industry is divided intosubsegments, including logic ana-lyzers, emulators, pattern genera-tors, temperature sensing equip-ment, counters and oscilloscopes.

The increase in power combinedwith lower prices are the drivingforces: Instrument designers arefinding it more feasible to incor-porate their products into a PCthan to build PC -like componentssuch as CPUs, digital memory ordisk drives into their instruments.

CRT safety standard updateUnderwriters Laboratories is

proposing the updated Standardfor Safety for Implosion -ProtectedCathode -Ray Tubes for Television-

Type Appliances, UL 1418, forrecognition as an American Na-tional Standard.

The scope of UL 1418 coversimplosion -protected cathode-raytubes, including television picturetubes and display tubes employedin appliances and business,

medical, and dental equipment.The scope also covers implosion -

protected cathode-ray tubes thathave been in service and subse-quently rebuilt or remanufactured.

UL is seeking review and com-ment from interested individualsand organizations to help developa consensus upon which continuedrecognition of UL 1418 by theAmerican National Standards In-stitute (ANSI) can be based. ANSIis a clearinghouse for informationon standards and coordinates

development of national consensusstandards through voluntary ac-tion.

Anyone interested should con-tact Mavis Whitehead at UL, 333Pfingsten Road, Northbrook, Il-linois 60062; 312-272-8800, ext.2988, and request a free copy ofUL 1418 -NR. Those interestedshould request their copy im-mediately so that their commentscan be considered in time to meetthe January 13 UL deadline forthis standard. WWI

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Repairingthe consumer

color vídeocamera

PART 2

Understandingand using the tools

The successful repair of anypiece of equipment depends notonly on the knowledge of the itembeing serviced, but also on usingand understanding the propertools and test equipment.

Before you attempt to make arepair on color cameras, you musthave three elements: First, youmust create the right environ-ment; second, you must have theright test equipment; and third,you must understand how to use it.No other kind of video product inneed of repair is as unforgiving asa color camera. Each adjustmentis dependent upon the precedingone. Even after a color camera hasbeen properly adjusted, whetheror not its performance is regardedas satisfactory depends somewhaton the opinion of the viewer.Because the successful repair of acolor camera is so dependent uponthe viewing of the output signal,this article includes the setup andusage of several important pieces

of test equipment: the videomonitor, the vectorscope, lightingand test charts.

The right environmentCreating the right environment

begins with positioning the cameraapproximately six feet from thetest chart. This allows for settingthe back focus so that objects willremain in focus throughout the en-tire zoom range of the lens. Boththe plane of the camera and theplane of the test chart must be ab-solutely level. This is essential ifthe yoke is removed, as its positiondetermines tube deflection. Onlywhen the object the camera isviewing is level can the yoke be ad-justed to show a horizontal plane.Many manufacturers recommendthat prior to any adjustment thecamera and test chart be checkedwith a leveler.

The importance of lightHuman perception of color is a

By Neil Heller

complex phenomenon based onhue, saturation and brightness.Because what we see as an objectactually is the light reflected fromit, camera adjustment must takeinto account the color of the lightilluminating the object. Althoughthe object will color consistently asa function of its makeup, the il-luminating light will not. As thelight source changes, the propor-tions of color balance can change.We express these as changes incolor temperature, which is basedon the color of the light emittedfrom a blackbody raised to aspecific temperature. A blackbodyis defined as a body which, if such athing actually existed, would ab-sorb all of the light that strikes it.The closest thing to a blackbodyis lampblack, which absorbs ap-proximately 99% of the light thatstrikes it.

As a blackbody is heated, the col-or of the light it emits changes asthe temperature changes. These


changes are expressed in theKelvin degree scale, whose zerovalue represents absolute zero. Ata temperature of 3200°K, theblackbody will appear red. At5500°K and higher, the blackbodywill take on more of a bluish hue.Color temperature has no relation-ship to the temperature readingsused for reporting weather condi-tions. Therefore, while a cloudyday will normally have a lowertemperature than a sunny day, itscorresponding color temperatureis higher.

These temperature values can beapplied to the light given off byvarious types of lighting. For ex-ample, light in a room illuminatedby fluorescent lights will have acolor temperature of approximate-ly 4500°K. Sunlight filtered bycloud cover can create colortemperatures as high as 8000°K.These different values of colortemperature emit different colors,but to our eyes, a white piece ofpaper viewed under all these con-ditions would still appear white.

Image pickup devices do nothave the same ability as our eyes.Changes in color temperature willunbalance the unity of the threeprimary colors that is required forreproducing white as white. TVcameras are preset at the factoryto exhibit a unity -color readingunder a color temperature of3200°K, which is the color emittedby halogen lighting. This type oflighting is used as a standardbecause its characteristics areclosest to those of naturalsunlight. A properly setup camerawill see a white object as whiteunder these conditions. Move thesame camera outdoors, or changethe type of lighting, and the whiteobject will take on the prevailingcolor of the new lighting source.For example, as noted before, ascolor temperature increases, sodoes its blue content. Our whitepiece of paper viewed outdoors ona cloudy day would appear blue tothe color camera.

In order for a color camera tocorrectly reproduce color aslighting changes, it is necessarythat color temperature sensed bythe pickup tube remain constantregardless of the light source. Ofcourse, this is impossible to do by

natural means alone. To ac-complish this, cameras use eitheran optical or an electronic methodor a combination of both to causethe camera to believe it is seeingan object under 3200°K lighting.Most industrial grade single -tubecameras and all 3 -tube camerasuse an optical color filter wheellocated in front of the pickup tube.Usually this filter system will havea number of filters to compensatefor varying lighting conditions andone setting to block completely alllight transmissions to the tubewhen the camera is not in use.

In order to achieve uniformlighting conditions during servic-ing, it is best to work with twolamps that are angled toward thetest object. The best way to deter-mine lighting uniformity is to use alight meter and measure the lightaround the perimeter of the object.Remember that if the light level isonly specified in the servicemanual in lux, this specificationmust be divided by 10 in order tofind the light level in footcandles.Once again, remember that thecolor camera is designed tooperate under a color temperatureof 3200°K, as this temperatureprovides the proper balance be-tween red, blue and green, whichare the three primary colors thecolor camera needs to see in orderto produce white. Therefore, anylight source used to set up thecamera must generate this colortemperature.

Using test equipmentAny type of camera operation or

attempt to judge camera perform-ance based on specifications reliesupon the operator's ability tounderstand test equipment. Toooften, hours, days and evenmonths of production have beenwasted due to the improper setupof the color camera. This sectionwill review the operation and in-terpretation of waveforms andhow they are read by both thewaveform monitor and vec-torscope.

The waveform monitorA waveform monitor is a highly

specialized type of oscilloscopethat is applied only to making cer-tain TV waveform measurements.

It sacrifices the flexibility of anoscilloscope for the ability tomeasure TV signals quickly andaccurately.

Any discussion of waveformmonitor operations begins with anunderstanding of how to read itsfaceplate. The waveform monitoris used to measure the timing andamplitude of the NTSC compositesignal representation of TV ver-tical and horizontal lines. Let'sbegin by interpreting the faceplatemarking. Previous measurementsof video signals have been in termsof voltages. The waveform mon-itor expresses these voltages inIRE units. The IRE scale wascreated by the Institute of RadioEngineers, and looks at the videosignal as a relative measurement,not in absolute terms such asvoltage measurements.

The reference point for the IREscale is the zero (0) IRE mark. Thepart of the TV signal in a positivedirection from the 0 IRE point isthe active video. Signals in thenegative direction from the 0 IREpoint extend from the blankinglevel to the lowest point of the syncindicated on the faceplate.

In the controlled environment ofa TV broadcast studio, videowaveforms are a standard ampli-tude of one volt each, measuredacross 7511, and also measuredfrom the most negative point onthe sync pulse (the sync tip) to thereference white level.

Under these conditions, 0 to 100IRE units represents a voltage of0.714V. Within this range of activevideo, located between the 0 and20 IRE markings, is the 7.5 IREpoint. This is known as thepedestal level, and it representsthe blackest point of the activevideo signal. By setting thepedestal level no lower than 7.5IRE units, we protect the darkestlevels of the scene from fallingbelow the 0 IRE level. If this oc-curs, the TV set might mistake thevideo's pedestal for sync and beginto start a new horizontal field inthe middle of active video. Becausethe 7.5 IRE level is the startingpoint in terms of signal amplitude,it is usually referred to as the"setup level."

The negative transition from 0to -40 IRE units is equal to 0.286V.


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The waveform monitor (left), is a highly specialized type of oscilloscope used formaking accurate measurements on video waveforms. To the right is a vectorscope, atest unit that complements the waveform monitor by measuring chroma/burst phas-ing and color saturation.

For this photo, the waveform monitor was set up to show the waveform of twohorizontal lines of TV information.

The faceplate looks like this when the waveform monitor is adjusted to display twocomplete video frames.

Therefore, the 140 IRE units oftotal video signal can also be refer-red to as a 1Vp-p signal.Theoretically, the only limits onthe camera signal levels resultfrom the electronic construction ofthe camera. Most single -tube, andall types of 3 -tube color camerasprovide controls for adjusting theamplitude and phase of the syncsignals. Prescribed limitations forsync and video levels are the resultof the need to maintain consisten-cy between camera and monitor.Sync levels are preset by the needof the monitor to reference to alevel of 0.286V. Limits on thewhite level are due more to thecarrier limits with the bandwidthof the TV channel, than to the elec-tronics of the camera or monitor.

In a closed circuit system, wherethe signal is not transmitted bymeans of RF, the consequence ofincurring video levels over 100IRE will be minor loss of detail inthe high light areas. However, inRF transmission, as the video levelincreases, so does the frequency ofthe RF signal. If the video level isnot limited, the RF carrier can ex-tend beyond 4.2MHz. As the car-rier approaches the 4.5MHz soundcarrier, there is a chance that thevideo can bleed into the audio andcause interference. Another wayof looking at this situation is interms of the carrier output. Theamount of output carrier is deter-mined by the strength of themodulating video signal. Thehigher the de level of the videosignal, the lower the carrier out-put. The value of the RF carrier atany given video level is rep-resented by the right-hand set ofmarkings on the faceplate of thewaveform monitor.

The lowest point of the syncsignal is the maximum amount ofcarrier (100%) and therefore mustbe represented by the same valueon every horizontal line. Theblanking carrier represents 75% ofthe carrier. Reference white isconsidered to be, under normalconditions, the highest level of thevideo picture. Although thereference white level is not fixedon every horizontal line as is sync,it is important that it not exceedthe 100 IRE level. This level


vs4°Ono"

FEBRUARYDevelopments in soldering and desolder-ing-One thing that has remained remarkablyunchanged about electronic circuits is the factthey are connected, physically and electricallywith solder. Much has changed, however, aboutthe methods of using solder to manufacture cir-cuits, the tools used to desolder, remove andresolder components, and the techniques usedto perform these operations. This staff -preparedarticle reports on the latest in soldering anddesoldering products available, and describestechniques to use and precautions to observe inreplacing components in today's circuits.

Servicing video cameras, part 3-When a colorvideo camera needs servicing, sometimes it onlyneeds adjustment. In other cases, replacementof components is required. This article describeshow to adjust the camera for the best pictureand how to determine when the pickup tubemust be replaced when it has been damaged orhas aged beyond its useful life. Also discussedis how to set up the test equipment for best testperformance.

Servicing the Wards model GGY16229A-HomerDavidson describes the theory of operation ofseveral of the circuits in this set, including suchsections as the voltage regulator and startupand shutdown circuits. The author exploresseveral areas that are most likely to cause prob-lems and describes troubleshooting them.

What do you know about electronics? Padders,capacitors and finding the right resistance -Oscillators are at the heart of many electronicsystems, notably communications products.This article explores the placement of padders inthe circuit to obtain proper frequency tracking.Also discussed is a method of obtaining the cor-rect value of resistance from your junk box toconstruct a given circuit.

represents 12.5% of the peak car-rier value. Signals higher than thisvalue will cause two undesirableeffects. First, the carrier powerdrops so low that any type of noisemay interfere with the quality ofthe receiver picture. Second, thelack of video carrier creates an in-sufficient 4.5MHz audio carrier.This results in a buzzing sound asthe video is heard in the audio. Youmay have experienced this whilewatching a TV program whenwhite lettering is superimposed onthe screen.

As the white level varies due to anumber of factors such asreflected light and lens opening,the camera system allows sometransitions over the 100 IRE level.The camera's white level usually isset between 110 and 120 IREunits. This is a 10% to 20% in-crease in signal level, and resultsin an additional 12.5% loss of car-rier power, reducing it to zero.Naturally, continuing to operate atthis level would render the pictureunstable. This should make it ob-vious that monitoring the camera'ssignal level using the waveform

monitor is a critical part of anyvideo production.

Up to this point, we have onlyspoken about B&W signals. Colorsignals have the addition of theback porch burst signals. The 0.3Vburst signal is positioned betweenthe -20 and + 20 IRE levels. TheTV system sees the average ofthese burst sine waves as an aver-age level of 0 IRE, so there is nodanger that the transition below 0IRE will be mistaken for sync.

Using the waveform monitorfor timing measurements

The waveform monitor also canbe used to confirm signal pulsewidths. In order to do this, wemust change the operating modeof the waveform monitor. Foramplitude measurements, thewaveform monitor's sweep was setto display two horizontal lines(2H). To measure signal timing,change the sweep to show 1µs perdivision. In this setting, the largerdivisions located at the 0 IRE linerepresent 1µs, while the shorterdivision markings represent areading of 0.20.

In our continuingefforts toserve you...

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For this display, the waveform monitor was set at 1µs per division. Shown, starting atthe left: horizontal blanking, then the sync tip and at right, the color burst.

!WI!. }-. ... ..

..Ilw , iryl/

This closeup view shows only the chroma portion of the video waveform.

The vectorscope display gives information about TV signal phasing.

After timing measurements aretaken, you may wish to use the twovertical sweep modes of thewaveform monitor. This modeallows you to observe one completeframe of video. Although timingdurations are hard to see, this canbe used to show problems that oc-cur over long time durations. Thesecond waveform monitor mode isknown as the response mode. Alltiming and amplitude measure-ments can be made in the flat modethat displays all aspects of thesignal. In some cases, when at-tempting to take amplitudemeasurements of a color signal,the chroma, (which, like a burstsignal, is a 3.58MHz sine wave) candistort the reading. For thisreason, the operator may choose touse the IRE response position inorder to filter the burst andchroma information. On the otherhand, should the operator need toview only the 3.58MHz informa-tion, the chroma response modecan be used.

The final operational mode is thedifferential gain (Diff. Gain). Thismeasurement shows the relation-ship between chroma andluminance amplitude. For normaloperations, there should be nochange in chroma amplitude.Because this is a function of- thecamera's encoder, the measure-ment usually is taken by selectingthe camera's internal color bargenerator.

The vectorscopeThe functions of the vectorscope

complement the functions of thewaveform monitor. The waveformmonitor will indicate the presenceof a color signal by showingwhether or not it contains burst,but it is unable to indicate thephase of the signal. And themonitor indicates luminance interms of voltage levels. The vec-torscope performs two other func-tions required to adjust a videocamera properly: It shows phasingbetween chroma and burst, and itshows the strength of the colorsignal in terms of saturation.

The concepts of the operation ofthe vectorscope begin with thetheory of how the eye sees color.The eye interprets color on thebasis of the theory that mixing twoprimary colors results in the crea -


lion of a secondary color.By picking a primary color start-

ing point, such as green, you cantrace the additive and subtractiveprimary and secondary relation-ships around a color circle untilyou return to green. Differentprimary and secondary colors canbe expressed as different points onthis circle. Studies have shownthat, starting at any point on thiscircle as a reference color, thehuman eye will perceive a colorchange approximately 3.6° in anydirection from this point. As aresult of the additive process ofprimary colors, each secondarycolor is a result of adding twoprimary colors. For example:

Green + blue = cyan, which ispositioned between green andblue on the color circle.

Blue + red = magenta, which ispositioned between blue and redon the color circle.

Red + green = yellow, which ispositioned between red andgreen on the color circle.

The vectorscope displays therelationships of colors in verydefinite terms. Burst is used as thecolor reference point, and islocated at the 180° point. The cor-rect phase and saturation for eachcolor is noted on the vectorscopefaceplate by a group of inner andouter boxes. For color phasing, theinner boxes represent a phase dif-ference of + 1, -2.5°. The outerboxes show a phase difference of*10°. Note the 2.5° representedby the vectorscope's setup arewithin the 3.5° phase limits of hueshifts sensed by the human eye.

For saturation adjustments, theinner boxes represent changes of*2.5 IRE and the outer boxesrepresent changes of *20 IREunits. Using the waveformmonitor, we were able to check dif-ferences in chroma that resultfrom changes in luminance levels.With the vectorscope, we cancheck changes in chroma phasethat are caused by changes inluminance. A series of additionalboxes is used to indicate shifts of10° above and below the 180° to0° point. Shifts to the plus andminus side also can be used todetermine differential phase.

Using test chartsfor setup, alignment, balanceThe goal of any color camera

setup is to produce a good qualitycolor picture that is an exactreproduction of the original scene.For this reason, just as the typeand amount of light are specifiedto set up the camera properly, soare the objects that are viewedduring setup.

These objects are known as testcharts. Depending on their subjectmatter, they can be used not onlyfor camera setup, but also fordetailed alignment and determin-ing camera specifications. For3 -tube camera setup, the mostcommonly used charts will be theregistration and B&W log reflec-

tance chart. The registration chartis used to align the individual red,green and blue tubes so they scanthe objects in the same way. TheB&W log reflectance chart is usedto adjust for proper color balanceso that B&W objects will appearblack and white to the colorcamera.

Although registration is a mat-ter of being right or wrong, colorbalance can be a matter of opinion.To begin with, the operator'sjudgement is dependent upon thecondition of the color monitor. Forthis reason, when using a colormonitor to judge the results of col-or balance, the monitor must beconsidered as a test fixture. Assuch, the monitor must be properly

Yellow


This closeup of the vectorscope faceplate shows the setup boxes for color phaseand chroma amplitude.

adjusted prior to íts use.The best way to adjust the

monitor is to use a knownreference signal. A good source isthe camera's internal color -bargenerator. All three tubes andmost industrial type signal -tubecameras contain such a generator.Monitor setup begins by turningoff all of the monitor's automaticmodes. As with the automaticcamera presets, monitors presentinput signals to preassigned levelsthat will not vary, regardless ofchanges to the input signal.Therefore, the use of automaticcontrols will mask any changes tocamera setups. Any attempt to setup a camera using a monitoroperating on automatics can be anextremely frustrating experience.

The next step is to adjust thebrightness and contrast controls toshow clearly all the individualshades of gray. When themonitor's gray scale is clearlyshown, turn up the chroma untilthe edges of each color bar aredistinguishable from one another.

If the chroma is set too low, thecolors will look faded. If thechroma is set too high, the edges ofeach bar will look blurred.

The final adjustment is hue, ortint. If you do this adjustmentwrong, your blues will look red andyour reds will look blue. As mostshooting centers on people, thecamera ordinarily should producethe best possible skin tones. Thesame is true for the monitor. To dothis, adjust the tint for the bestpossible yellow reproduction. It isalways a good idea to performthese simple and quick monitorsetup procedures and comparethem to the monitor presets.Remember to leave all monitorautomatics off during camera ad-justments.

Manual color balance setup of acamera requires using a log reflec-tance chart and a waveformmonitor. The reflectance chartcontains two of the nine mono-chromatic chips that provide thecamera with a range of reflec-tance. This range begins with a 3%

reflective black, which yields a 7.5IRE pedestal level, and a 70%reflective white that yields a 100%IRE level. The waveform monitorallows you to see differences ineach of the individual tube chan-nels. These differences are shownas the presence of chroma whenthe camera is focused on themonochromatic gray scale. Thischroma causes the chart to appearblue, green or red, depending onthe level most out of adjustment.Color balance is achieved when allchannel gains are at unity. At thespecified sensitivity level, all chan-nels will have a pedestal of 7.5IRE, and a white level of 100 IRE.Then, the chroma subcarrier isnulled, to appear only if thecamera focuses on a colored object.

Usually, manual operator colorbalance adjusts only the red andblue levels. As with the registra-tion setup, the green channel isused as the reference setting.Green pedestal sometimes is usedas the camera's master pedestal,while the 100 IRE level is set byopening the lens iris. Red and bluepedestal and white levels are thenused to match gains. Using thewaveform monitor allows theoperator to perform these ad-justments quickly by minimizingsubcarrier at the pedestal andwhite levels. In addition, theoperator can confirm and adjustthe horizontal and vertical blank-ing widths. Any shooting that willbe subject to post productionshould have all its H and V blank-ing set toward its lower limits inorder to compensate for pulsewidth expansion. The waveformmonitor is also a tool that shouldbe used during the actual shooting,to prevent video levels from risingabove the 100 IRE levels and slip-ping into the audio carrier.

Single -tube color cameras havean advantage over that of 3 -tubecolor cameras. They do not requirethe registration of the individualred, green and blue signals. Themost critical adjustments for asingle -tube color camera aredeflection, which requires the useof a white card, and color balance,which requires the use of a reflec-tance chip chart. «WU


AnImportant Notice

PROCEDURE FOR CLEANINGUPPER CYLINDER UNIT

1. Position the video head to permit access for cleaning andhold the upper cylinder to keep it from turning whilecleaning.2. Gently rub the video head in direction of tape travel withhead cleaning stick (CFK27) moistened with Freon TF.3. Repeat for the other video head

UPPERCYLINDER

VIDEO HEAD

CLEANING STICK

Note:1. Do not rub vertically.2. Do not apply any pressure to head. If contaminant is noteasily removed, continued gentle wiping will usually removethe contaminant.

In the October 1985 issue of Elec-tronic Servicing & Technology, wepublished an article on page 37 en-titled "Servicing video recorders,Part 3: Preventive maintenance fora VCR." In that article, on page 40,under the heading "cleaning thevideo heads," the article recom-mends, "To clean the heads use alint free material dampened with afreon compound. Many video storessell video head cleaning tabs. AQ -tip also can be used but be sure totwist its end so the fibers will com-press."

Since the time that issue waspublished, we received a letter fromDon Hatton, Director of ProductServices, Consumer ElectronicsGroup, Electronic IndustriesAssociation, concerning the article.In that letter, Mr. Hatton says "Inregard to cleaning the video heads,the method outlined using a lint -

free cloth or a Q -tip is verydangerous. Our manufacturersrecommend the use of head cleaningsticks as illustrated here. The

method described will provide ade-quate results with the least possiblechance of damage to the videoheads."

In the same article, reference ismade on page 41 to "Replacing thevideo head." Mr Hatton's letterpoints out that replacement of theupper cylinder is preferred to thereplacement of an individual head.Actually, the procedure describedis for the replacement of the uppercylinder, not an individual head.Unfortunately, the word "head"was used instead of the term "upperhead cylinder."

Electronic Servicing &Technology endorses both of theseprocedures recommended by theEIA. Don't clean the video headswith any materials other thanthose recommended by themanufacturer, and don't even tryto replace individual videoheads. When the heads needreplacement, replace the entireupper head cylinder.

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What do youknow aboutelectronics?

Radioreceivers

andbidirectional

busesBy Sam Wilson

The first practical applicationsof electronics were in the field ofcommunications. Because it is theoldest use, the variety of receivertypes might be expected to bealmost endless.

Actually, in the history of com-munications, there are relativelyfew types of receivers. Seven ofthe most important types arelisted here:

Crystal inputRegenerative

Super -regenerativeTuned radio frequency (TRF)

SuperheterodyneReflex

Homodyne

Each type of receiver listedabove has advantages and disad-vantages, but the superheterodynehas become the most popular. It isnot perfect by a long shot, but ithas reasonably good sensitivityand selectivity.

Some other types have eitherbetter selectivity or sensitivity.The regenerative and super -regenerative types can be better inboth categories, but they haveother disadvantages that have tobe considered. For example, theyradiate interference signals, andthey have terrible fidelity.

The most important disadvan-tage of the superhet receiver is itspoor (not terrible) fidelity. Unlessthe designer spends a considerableamount of effort and money on theIF section, this type of receiverwill not produce a flat responseover the range of frequencies re-quired for a faithful reproductionof the modulating signal.

If you have ever performed asweep alignment on the IF stageof a superhet, you are well awareof the problem of frequencyresponse for that type.

The homodyne receiverThe homodyne receiver is con-

sidered by some technicians to besuperior to the superhet.

In the early 1930s, the patentsfor the superheterodyne receiverwere held by companies in theUnited States. That meant com-panies in England would have to

46 Electronic Servicing & Technology January 15'86

pay royalties to U.S. companiesfor the right to manufacturesuperhet radios.

To put it mildly, they didn't likethe idea. Engineers in England setout to design a completely newtype. They called it the homodynereceiver.

Figure 1 compares the superhetand homodyne receivers. In thesuperhet, the local oscillator com-bines with the incoming RF signalto produce a difference (in-termediate) frequency. The lowerintermediate frequency remainsconstant no matter what the RFand is amplified before it isdelivered to the detector stage.

In the homodyne receiver, thelocal oscillator frequency is setequal to the incoming RF signal.That cancels the carrier, and allyou have left is the sidebands. Inan amplitude -modulated signal, allof the useful signal is in thesidebands.

Figure 2 shows what happens us-ing a time -domain display. Whenthe carrier is removed, there aretwo sidebands. Only one is neededto reproduce the original modu-lating signal, so a filter is used toremove the unwanted sideband.Then, all that is left is the originalmodulating signal.

Clearly, the homodyne receiver

has an advantage over thesuperhet. It has no IF stages toclip and distort the sidebandsbefore detection takes place, so itsfidelity is a great improvementover the superhet.

Additional RF stages could beadded to improve the sensitivity,but sensitivity is not a problemwith most consumer radio recep-tion today.

So, why didn't the homodynereceiver become the most populartype in the world?

One problem was that theoscillator frequency had to bemaintained exactly equal to the RFcarrier. In early versions, they

RFAMPLIFIER

Figure 1B.

MIXER

OSCILLATOR

AUDIO


tried to accomplish this with astable oscillator circuit. That didn'twork. A perfectly stable oscillatorat anything near a reasonable cost(and size) was out of reach in thosedays. Also, the transmitter carriermight drift a few hertz in a week.

Probably the most importantdisadvantage was that a certainamount of skill was needed to tunethe receiver to the station.

One solution: rename it!A superheterodyne receiver has

two detectors. The first detector isthe mixer (or converter) in the RFstage. Early textbooks referred tothe stage that we call tie detectoras being the second detector.

The homodyne receiver has onlyone detector, so it is a single con-version receiver. That is the nameit goes by in the United States.You have to look very hard to findthe name homodyne receiveraround here. There are some inno-vations in the modern single con-version receiver, due mostly to theadvances in modern technology,that help to justify the namechange. The fundamental prin-ciples haven't changed, however.

The most important advance isthe circuitry now available forlocking the local oscillator onto thecarrier. A phase -locked loop isavailable for this purpose. That'snot a new circuit, but it is availablein integrated circuit form and thatmakes it very convenient to use.

Figure 3 shows how to make asingle conversion receiver usingan integrated circuit phase -lockedloop (PLL). This circuit was givenin a Signetics catalog. I once had astudent build this receiver withvery good results, but it wassomewhat difficult to tune.

Maybe the fact that it is difficultto tune accounts for the absence ofhomodyne receivers from the mar-ket today. Radio receiver de-signers are convinced that anyradio with more than two knobs isbeyond the skill or comprehensionof the American public. This ideahas now spilled over to the designof TV receivers.

The 2 -way bus: How it's doneA bus is a combination of con-

ductors used to carry a group ofsignals. I still like the suggestion

Figure 2.

CARRIER

LOWER UPPERSIDEBAND SIDEBAND

Z1Z1Z11y4

11114111111111. 1A.1A

P11'1'y111111111111111111111111

OSCILLATOR

1-1;1"1j/1111111111111111

I.... A1" 2

11í1111íi

111/11i11111111.--^^

FILTER

-1-u_1_1-1-1111111/1111/11111411/111111411111

I

AM SIGNAL

CARRIERELIMINATED

AUDIO SIGNALREMAINS

of a man who was attending one ofmy lectures. He wanted to changethe name from bus to train(because they have conductors).

Take a dime and slice it into2,500 equal cubes. Then, mount1,700 transistors and associatedcircuitry on one of the cubes. Thatis the size of IBM's new semicon-ductor chip. They have made acomplete programmable logic ar-ray on that scale.

It makes you wonder about the

size of the conductors and buses ona chip that size. Whatever the sizeof the conductors, they reduce theamount of circuitry available.

One method used to conservespace is to use the same bus (orconductor) to carry information in-to or out of the chip. That requiressome special circuitry to preventthe possibility of signals trying togo both ways at the same time.

If a logic 1 (+ 5V) and a logic 0(0V) appear on the same conductor


ASE LOCKED AM RECEIVER

3 12

N E561 B(TOP VIEW)

4 5 In_aIEMOCULATED

OUTPUT

1

1 2k

+V

5k

TUNING(OPTIONAL)

TWO-WAY BUS

.111111- 4111111---- - - - - - la»

DATA DIRECTIONINPUT

E

E = 1

E=0 - -2111»

to the AND gatesHerter (for AND X)r AND Y). At firstiat the buffer couldecause it does notdifying the signal.ncluded in the Cir-ce a propagationin the enable logicturn, produce aid y at the same

gnals are always

opposite, so, it is not possible forboth AND gates to be on at thesame time.

The direction of the signal on thebus depends upon which AND isenabled. For that reason, theenable terminal is sometimes called the data direction bus ordata direction terminal.

Two-way buses also can be madewith ORs, NANDs or NORs. Theyare used both inside and outside in-tegrated circuits.

January 1986 Electronic Servicing & technology 49

Continued from page 7

OFF

1

LIGHT IN

LIGHT OUT

LIGHT IN

ONI .i./

/

/.-..-//I

.i-/i / /I LIGHT OUT(SCATTERED)/

I ;? /I /

RE: reflective electrodeTE: transparent electrodeLC: liquid crystal

Figure 2. In a dynamic scattering mode display, application of a sufficiently strongfield generates a strong turbulence, producing a white opaque appearance similar tofrosted glass.

LIQUID CRYSTAL MOLECULE

' PLEOCHROIC DYE

Figure 3. A guest host display uses a dissolved dye to achieve a wide viewing angle,brightness and good color brightness.

Figure 4. A standard twisted nematic display controls the liquid crystal molecule andmakes it act like a valve, either allowing light to pass through or shutting it off.

Twisted nematic displaysThe twisted nematic or TN

display, which relies on positivenematic materials, is now the mostwidely known type of LCD.Because of its low operatingvoltage (3V to 5V) and low currentconsumption, the TN LCD is in-creasing in popularity for largevolume applications.

A standard twisted nematicdisplay (Figure 4) controls the li-quid crystal molecule and makes itact like a valve, either allowinglight to pass through it, or shuttingthe light off.

Transparent electrodes controlthe alignment of the molecules inthe positive nematic material. Twopolarizers, one on the upper glassand one on the lower glass, arealigned so that they are off by 90°.If you try to shine a light throughthe cell, it will be polarized by thefirst polarizer and then blocked bythe second. The cell will always ap-pear dark.

The positive nematic liquidcrystal material in the cell isprepared so that its molecules lineup along the plane of each elec-trode. Because the two planes aredifferent, the orientation of thestructure rotates by 90° as youtravel from the upper electrode tothe lower one. This rotates thepolarized light coming through thetop polarizer by 90°, and allows itto pass through the bottompolarizer. This rotation of lightprovides the 90° twist that givesthese displays their name.

This is the normal condition ofthe display cell when the pixel isoff-when no voltage has been ap-plied to the electrodes. Whenvoltage is applied to the elec-trodes, however, the moleculesrealign themselves to follow aperpendicular orientation. So thetwist is eliminated and the cellswitches from light to dark. Thelight can't pass through the bottompolarizer. Removing the chargeapplied to the electrodes restoresthe twist.

The advantages of the twistednematic display are: low operating voltages (3V to5V) which allows low -voltage in-tegrated circuits to drive thedisplay. low operating power (as little as0.1µW per pixel) which makesthem suitable for portable opera-tion.


a well-defined threshold (about2V) that simplifies multiplexingand matrix addressing. the liquid crystal displaymaterial has a long life expectancybecause of the low voltages andcurrents applied.

Multiplexingand matrix addressing

A major technical problem offlat -panel graphic and videodisplays is addressing the hun-dreds of thousands of pictureelements (pixels). The major suc-cess of CRTs, in contrast, is aresult of the simplicity of rasteraddressing.

In a typical CRT, such as theones used in TV receivers, 250,000pixels are addressed 30 times asecond, with gray scale and colorinformation transmitted at morethan 6MHz. No flat -panel displayhas achieved this level of perform-ance.

Each pixel of a flat panel displayhas a row -and -column address. Amatrix of 480 rows by 500 col-umns, which is comparable to aTV, requires 250,000 individual ad-dresses. To use an individual wire

for each pixel is virtually im-possible unless the matrix is thesize of a billboard.

A pixel is usually a 2 -terminaldevice. When a voltage is appliedacross the two terminals, the pixelproduces a visible contrast. Inorder to accommodate all pixel ad-dresses, all of the pixels in the rowshare one terminal; all of the pixelsin each column share one terminal.To turn on a particular pixel, youmust apply a voltage across the ap-propriate row and column ter-minals.

Unfortunately, in this matrixscheme a fraction of the appliedvoltage exists across the terminalsof all pixels in the matrix. Thesepixels turn partially on, creating abackground image that reducesthe contrast of the image.

The problem of selecting aspecific pixel is compounded whena second pixel on another row orcolumn is selected. Ideally, onlythe two pixels would be energized;in reality, however, two additionalpixels would see the full voltageacross their terminals.

These two problems are inherentin the matrix addressing techni-

que. The solution to the fractionalvoltage problem is to use elementsthat won't turn partially on whenfractional voltage is applied tothem - devices with nonlinearproperties.

The solution to the multiple ad-dressing problem lies in line -at -a -time addressing. In this scheme,rather than tying together the rowterminals of the pixels, these areaddressed individually. The con-troller addresses a column ter-minal and then each pixel line insequence. Then the controller ad-dresses the next column and eachindividual line terminal.

Due to the large number of lines,line -by-line addressing must hap-pen quickly; the controller mustaddress every line terminal in arow in the same time period that itpreviously took to address the en-tire row. As a result, the displaymust be responsive to a short dutycycle. The individual lines are ad-dressed in sequence - they time-share the address cycle. This time-sharing is called multiplexing.

The duty cycle is determined bythe number of lines that must beaddressed within one cycle. A

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2

3

Materials

SurfaceAlignment

PanelDesign

Synthesis of new LC compounds.(Elastic constant, viscosity, dielectric anisotropy)

Mixing technologies of LC compounds.(temperature range, arrangement of constant)

Development of new surfactant and method of treatment 1

Control of tilt angle, domain of LC molecules

Suitable design of thickness, birefringence of LC materials

Geometric angle design of polarizers

Figure 5. LCD technology is advancing in several areas: materials, surface alignmentand panel designs.\ IIIIIIIIIIIIIIIIII I II

\//1,,P\/ I I I I I 111111111

\ I 1 1

\ 11111111111

(a) NEMATIC (b) SMECTIC A

1111 11/01/10/1//1

1111 /11111111/1/illffil

Ic) SMECTIC C

Figure 6. The molecular structure of the three most important classes of liquidcrystals: nematic, smectic A and smectic C are contrasted here.

n: PIRECTOR

p: SPONTANEOUSPOLARIZATION

Figure 7. Smectic C liquid crystals have the potential of being ferroelectric andtherefore suitable for LCDs.

1/200 cycle, for example, meansthat during every addressing cy-cle, the controller must address200 lines.

Recent improvementsin simple matrix displays

There is no all-around flat -paneldisplay that's perfect for every ap-plication, but for portable applica-tions, LCDs are filling more andmore needs. In fact, as the displaysimprove, it's hard to imagine anapplication that LCDs won't beable to satisfy.

And there's steady improve-ment. Several factors have con-tributed to this, as shown inFigure 5: improvements in liquid -

crystal materials, surface align-ment and panel designs. Of these,the improvements in materialshave been the most significant.

Two emerging LCD technologieshold particular promise. The firstis a supertwisted nematic display,where light passing through istwisted by 270°.

The supertwisted nematicdisplay will provide high multiplex -

ability of more than 200 lines withgood contrast. This is because ofits well-defined threshold. Unfor-tunately, the supertwisted displaywill have the same slow responsetime as a conventional TN display.

Ferroelectric smecticThe second emerging LCD

technology with promise is anLCD based on ferroelectric smec-tic materials.

The ferroelectric smectic displayuses a smectic liquid crystalmaterial in a simple new geometricstructure. A ferroelectric materialis simply a crystalline materialwhose polarization can be con-trolled by an electrical field. It isoften referred to as smectic C.

Smectic C materials promise toprovide displays with both an ex-tremely fast response time and amemory. The rapid response timewill be important in displayinghigh -resolution graphic images,and the memory means that thedisplay retains what you write toit-the image won't have to berefreshed. This last quality isespecially important for reducingthe power consumption of displaysused in portable equipment.

Figure 6 contrasts the molecu-lar structure of the three most im-portant classes of liquid crystals:


inematic (N), smectic A and smecticC. Neither nematic or smectic Aare ever ferroelectric. Smectic C,however (Figure 7), has the poten-tial of being ferroelectric andsuitable for LCDs.

In a smectic C display (Figure 8)the smectic layers are alignedparallel to the glass surface. If theliquid crystal material is thinenough, the surface interactionswill unwind the helix. This unwind-ing action gives the material itsferroelectric properties. A pulsedelectric field switches the polariza-tion of the cell. The closeness ofthe surfaces causes it to latch inthat state, maintaining it in-definitely after the pulse is over.Polarizers produce a visible con-trast between the two states of thecell as the light is shining through.

Because of its speed and imagequality, the ferroelectric smectic Cdisplay is probably the best forhighly multiplexed displays. Butdevelopments won't come easy.Very few ferroelectric materialsare available now.

Active matrix LCD displaysSimple matrix displays satisfy

Figure 8. In smectic C liquid crystals, an unwinding action gives the material its fer-roelectric properties.

the demand for flat -panel displaysin many applications. And, in re-cent years, the technology oftwisted nematic or TN displays hasbecome extremely sophisticated;driving them at high multiplexingrates has made them suitable forproducts such as portable com-puters and pocket televisions.These products often use largenumbers of scanning lines,sometimes more than 400, requir-

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FOR MORE INFORMATION SEND BUSINESS CARD TO:NESDA COMPUTER GROUP, 2708 WEST BERRY STREETFORT WORTH, TEXAS 76109; PHONE (817) 921-9061

ing a highly multiplexed drivingmethod.

The operating principles of TNdisplays unfortunately dictate thatas the duty ratio becomes higher,the image quality - that is, the con-trast ratio and viewing angle-degrades. As a result, when adisplay is driven in a non -multiplexed manner, Its contrastratio might be 20:1. When thedisplay is multiplexed at a duty

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I VII1:1r1.19./va.1.1.1 ,.1~..1.1aCircle (15) on Reply Card


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ratio of 1/200, the contrast ratio isI 3:1.

This limitation results from a

DATA LINE PIXEL

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SCANNINGELECTRODE

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SCANNINGELECTRODE(ITO)

elements. These applications yieldto metal -insulator -metal or MIMdiodes. Requiring a much simplerfabrication process (Figure 11).MIM displays can be made usingonly two or three photo masks,compared to the four required tomake TFT displays. The metal filmused to create the diode isdeposited by a sputtering process

Figure 12. In an MIM LCD. the driver diodes have a stable threshold voltage; once the thatmakes it fairly easy tovoltage applied exceeds the threshold the on current flows. Dropping the voltage fab rlcate displays that are overbelow the diode's threshold turns the current off. 10 -inches diagonally.

A lateral structure, developed byEpson, makes large -area fabrica-tion even easier.

Figure 12 shows the structure ofan Epson MIM LCD. The driverdiodes have a stable thresholdvoltage; once the voltage appliedexceeds the threshold the on cur-rent begins to flow. Dropping thevoltage below the diode's thresholdvoltage turns the current off.

A new MIM LCD displays 400 x640 dots with a pitch of 0.3mm inboth the horizontal and verticalaxes. In a reflective display, wherethe light source enters from thefront of the display, we easily canobtain a contrast ratio of 15:1 anda viewing angle of over 50°. In thisdesign, each dot to be displayed isdivided into two pixels so that,even if a pixel fails, the dot will bevisible. This increases both fabrica-tion yield and the display'sreliability.

The specifications of our new5.13 -inch color TFT LCD and 400x 640 dot MIM LCD are summariz-ed in Table 1. Both offer an ex-cellent image quality: high con-trast ratio and wide viewing angle.

In a small display, such as theone in a pocket television, theproblem isn't as serious becausethe cost will go down with thelearning curve associated withmanufacturing these devices. Butmanufacturing a large area displaycosts more than it costs ento make aCRT.

GLOSSARY OF TECHNICAL TERMS

active matrix - an arrangement in which the display contains the driverelements.armorphous silicon -a non -crystalline form of silicon commonly used tofabricate flat -panel displays because it is easy to work with.contrast ratio - the ratio of a display's maximum luminescence to itsminimum luminescence.ferroelectric -a material whose polarization can be controlled by an electricalimpulse.liquid crystal -a liquid of rod -shaped molecules that features many of the op-tical characteristics of crystal.luminescence-a measure of the strength of the image received by a person.pixel -a single element of a picture, such as dot on a display screen.polarizer -a plastic film that filters light passing through it according to thelight's orientation.radiance - the rate of energy flow from an electromagnetic source (measuredin joules/second or watts).static drive - an arrangement in which the driver elements are external to thedisplay.thin film -a method of making devices in which components are created bythe deposition of a thin film of some material.

TYPES OF LIQUID CRYSTALS:

LCDs are made from three types of liquid crystal materials.

cholesteric - The individual molecules of the liquid crystal are aligned parallelto each other, however the molecules are grouped in layers; each layer isrotated relative to the previous layer by a few degrees producing a helical ar-rangement.nematic-These molecules are aligned with their long axes parallel to eachother, but the molecules are free to move up and down. There are no distinctlayers of molecules.smectic - The individual molecules are parallel to each other, but confined todistinct layers that are also parallel to each other; there is no rotation betweenlayers. There are at least nine types of smectic materials.

M


The Photofact folders for TV receivers and otherequipment have been released by Howard W. Sams& Company since the last report in ES&T.

GOLDSTARChassis NF9X 2371-1

GOLDSTARChassis NT -01X 2373-1

KTVKCT1950 2370-1

KTVChassis KAC-1901 2374-1

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QUASARChassis AMDC110F 2370-2

SANYOChassis A6S-47100 2372-1

SEARS564.43030450.564.4303045 2373-2

TOSHIBAChassis TAC8430, TAC8432, TAC8436 2372-2

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WARDSGNB17916A/B/C, GNB17926A/B/C 2371-2

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Plug in!To the NESDA system.

YOUR BUSINESS is in the world's fastest changingindustry. If you're not careful, you could findyour business in the dark.But, you don't have to stay there.

Through a system of local, state, and regional groups,the National Electronics Sales & Service Dealers Assn.(NESDA) keeps members up-to-date with the fast paceof advancing technology while offering:

Managerial and technical training. Business contacts. Technical and management certification. Information on new products. Legislative activities that affect the industry.

Don't be left in the dark. Let the NESDA system workFOR YOU!

For more information and an application, write toNESDA, 2708 W. Berry St., Ft. Worth, TX 76109; Ph (817) 921-9061

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Symcures WantedElectronic Servicing and Technologyneeds a broader variety of television Symcures.Especially needed are reports of Quasar,General Electric, Sylvania (or Philco), Sony Searsand Magnavox.

Symcures are, by definition, solutions toproblems that have been encountered during therepair of more than one television set of thesame make and model, and that may reasonably beexpected to be a source of recurrent failure.

Please give the brand, model number.Photofact number, a brief description of thesymptoms, a rough hand -drawn schematic of thearea containing the defect, and a shortdescription of the cure (including whether thedefective component was open, leaky, shorted orintermittent).

ES&T editors will adapt the material to theSymcure format and have Photofact-styleschematics prepared.

Send seven Symcures each time. Only six willbe published, but the extra gives the editor aspare for one already printed in the past (orotherwise not suitable to the format). $30 will bepaid for each page of six actually published(remember to include full name and address).

Send to: Symcure DepartmentElectronic Servicing and TechnologyP.O. Box 12901Overland Park. Kansas 66212


Vertical locks only on very weak signalsRCA CTC40

(Photofact 1030-2)

Because failure to lock on medium -to -strongsignals can be caused by the tuner, IFs, video, AGCor sync stages, a faulty circuit was my first objec-tive. First, I injected a video signal from a VA48 tothe sync separator base. The locking was good at allsignal levels. Therefore, the sync separator and ver-tical circuits must be working properly.

Then I injected video to the sync -amp base. Theset now locked well between weak signal levels andabout 1.5 times normal level. I decided this probablywas normal.

Injecting video at the first -video -amplifier baseallowed locking at all signal levels, but adjustmentof the vertical -hold control was touchy. From the im-proved locking, I concluded everything was normalfrom the first -video -amplifier base and onward.

Tuner substitution also improved the locking,which seemed to indicate the tuner was working butagainst an AGC problem. The RCA TelevisionWorkshop 5 contains a number of steps for isolatingAGC problems. Step one was to ground the RF AGCat the tuner. According to the booklet, "If a pictureis obtained by grounding the RF AGC, the problemis obviously in the RF AGC circuit."

When I grounded the RF AGC point, the lockingwas normal from weak -to -strong signals. Evidentlythe AGC circuit, and specifically the RF AGCbranch, held the major defect. But where? Carefulchecking of likely components revealed nothing. Idid the remaining steps suggested in the booklet,which pointed to AGC but did not pinpoint.

My confusion had turned to perplexity; I must beoverlooking something. I got out my "RCA Volume1," by Carl Babcoke, (from Tab Books) and read thecircuit description. After finding a nice drawing thatshowed RF vs. IF AGC do voltages for differentsignal levels, I checked those in my set against thedrawing. My television did not seem to have theright relationship at the various signal levels be-tween RF and the IF AGC do voltages. By adjustingthe noise control or inserting some do voltage at RFAGC point, I could shift the signal level where roll-ing occurred, but could not eliminate the rollingcompletely. Nor could I get the two voltages to trackproperly.

If some of you are wondering why I didn't checkfor a leaky MOSFET in the tuner loading down thetuner AGC, remember: Changing the tuner did notsolve the problem. Nevertheless, I decided to checkthe MOSFET anyway. According to RCA Volume 1,the voltage at feedthrough C17 (with green AGClead disconnected) should not exceed + 0.1V, and

the drain voltage should not exceed + 2V. My setpassed.

I would like to say I finally deduced the cause ofthis problem using logic, but I can't say that becauseI didn't use logic. A lot of searching for hints finallypaid off in The Color TV Factbook. It stated that dif-ferent problems with C5 (or C364 RCA number) inthe first -video stage could cause various symptomsincluding unstable sync and locking. I removed C5(20µF) and checked it, finding it almost open. A newcapacitor completely restored normal operation ofthe color receiver.

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My relief at finally having the receiver workingwas much greater than my curiousity about howthat little capacitor caused the problem; therefore, Ireturned the television to the customer withoutmaking any more tests.

Roger D. ReddenBeaver, WV

Editor's Note: C5 bypasses several signals and cir-cuits. The important one here is that C5 is connecteddirectly to the AGC-keying-transistor's emitter.When it opens, it allows distorted horizontal pulsesto be fed into the RF and IF voltages and the base cir-cuit of the first video amplifier. Mixing of strayhorizontal signals with the AGC and video signalscan cause some mystifying symptoms, as you havefound already. In general, check all AGC capacitorswhen the symptoms defy logic.


Diagnostic instrumentation kitsA line of diagnostic instrumenta-

tion kits offered by Spantafeatures several assortments ofprecision test instruments. TheKD-300 Series line and the moreversatile models KD-301 andKD-302 seat each instrument in acustom -fitted polyurethane pocketwithin an attache case.


Remote control transmitterPhilips ECG, a North American

Philips company, has introduced aline of remote control transmittersthat replace original equipmentunits used with TV sets, videocassette recorders and channelconverters. Seventy-one modelsavailable are in both infrared andultrasonic types, for use asreplacements of more than 170known -brand transmitters. Theunits are completely new, notrebuilt, and key functions andlegends are identical with those ofthe original types.


Complete PCB repair systemAPE model PRS-475 PG

features a microprocessor con-trolled plating center, capable ofdepositing 50µin. of gold for mil-

spec edge connector repair. Thesystem also includes the followingaccessories: desoldering hand -piece, solder iron, thermal tweezerwith 3 -blade sets, reflow soldertool with practice kit, miniaturedrilling system and circuit repairkit.

Circle (77) on Reply Cards.

DMM designed for lowlifetime costs

John Fluke Manufacturing an-nounces the 8842A 5-1/2 digitmultimeter, the second meter inthe 8840 family, a series of systemmultimeters offering varied levelsof performance.

Model 8842A offers enhancedmeasurement capabilities for such

applications as production test orresearch and development. Itfeatures increased performancewith its 0.003% basic do accuracyand 0.08% basic ac accuracy (atone year). It also features 100nVresolution for dc -voltage measure-ments, 1µA resolution for dc -current measurements, and1004 resolution for resistancemeasurements. Hermetically seal-ed, proprietary thin film resistortechnology gives the 8442A a2 -year calibration cycle and war-ranty period.


PCB gold repair serviceAlchemitron provides a cost-

effective repair service, specializ-ing in the gold contact areas ofbare or finished printed circuitboards. Solder splash, worn con-tacts, delaminating gold, corrodedtin/lead, pitting, step plating andmissing contact fingers - all areexamples of board problems thatcan be repaired. Whether it stems

PCB Gold Fingers S we

Before Repair

from the design, the manufactur-ing process, or develops in thefield, the problem can be solved ata fraction of the board value, ac-cording to this repair service.Typical turnaround time is 24hours on scheduled orders.

Circle (/9) on Reply Card

Answersto the QuizSee questions on page 28.

1. D. The component in (b) is aUJT. The one in (a) is a JFET. Theelectrodes on the UJT are: base 1,base 2, and emitter.

2. C. The tunnel diode is one ofthe fastest switches in electronics.

3. D. If you have studied whathappens inside a transistor youknow that deathnium trap is a fan-cy name for an imperfection in thematerial that the transistor ismade of.4. A. The shorter the rise time

the wider the bandwidth. An em-pirical equation that is sometimesused is given here:

bandwidth x rise time = 0.355. A. Duplexers are used in

radar antenna systems.

6. C. An example of where thislevel of current is used is inleakage current measurements.

7. B. Connect the meter sothat electrons enter the negativeterminal and leave the positive ter-minal.

8. C. This test is used to checkan amplifier for distortion. If thereis a change in current the full -cycleaverage is not zero. That meansthe amplifier has changed thecharacteristic of the input puresine wave, so the amplifier hasdistorted the signal.

9. C. It is a good idea to keepin touch with the basic principlesof physics.

10. C. The coil is pulsed for thistest. That causes it to oscillatewith the distributed capacity. Theresult is a damped wave that canbe displayed on an oscilloscope. Ifthe coil is defective the oscillationsdie out immediately.


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312-463-2499

Editor's note: Periodically Elec-tronic Servicing & Technologyfeatures books dealing with subjectsof interest to our readers. Pleasedirect inquiries and orders to thepublisher at the address given,rather than to us.

Understanding ComputerScience Applications, by RogerS. Walker, Ph.D.; TexasInstruments; 284 pages; $14.95.

Here is a book that provides aself -paced course about using com-puters to solve problems. Ex-amples of computer applicationsand programs are included. It isthe second volume in a planned setof books explaining the fundamen-tals of computers in comfortablelanguage and format.

Highly technical material ispresented in simplified fashion,leading readers through a reviewof basic computer concepts, thencovering serial, parallel and net-work communications; distributedprocessing; modeling and simula-tions of systems; graphics; andfuture applications. Each of theeight chapters contains a summaryand a short quiz to enable readersto gauge their progress.

Texas Instruments, P.O. Box 225474 Dallas, TX75265

Video Electronics Technology,by David Graham; Tab Books;256 pages; $15.95 hardbound,$10.95 paperback.

Keeping up with rapid advancesin technology is easier whenrelated information can be drawnfrom a single source. This bookwas written to provide a 1 -stopreference for developing videotechnologies from microwave andsatellite television to VCRs andlaser -scanned videodiscs. Someoneworking in any phase of video elec-tronics or an allied field, or simplyinterested in the subject, will finddetailed coverage, beginning witha review of the principles of B&Wtelevision and continuing with anupdate of present and futurerecording, playback and com-

munications systems.

Tab Books, Blue Ridge Summit, PA 17214

Digital Electronics: Theory,Applications, and Trouble-shooting, by Byron W. Putman;Prentice -Hall; 350 pages;$32.95 hardbound.

The author's enthusiasm for thesubject of digital electronics is in-fectious; he intends for this book tobe read, reread and kept at handfor constant reference. Directed tothe technician or those nearingtechnical proficiency, this textassumes that the reader has a solidbackground in basic electronicsand transistor theory. The lastchapter, which introduces dataconversion techniques, also re-quires an elementary knowledge ofop -amp theory.

No concept is introduced until itcan be applied immediately to thematerial at hand. For example,Chapter 1 introduces the conceptsof digital electronics and thebinary number system, withnumber theory held to a bareminimum. The introduction to thehexadecimal number system isdeferred until Chapter 12, when itlogically supports memory -mapping techniques.

Prentice -Hall, Englewood Cliffs, NJ 07632

Analog Electronics forMicrocomputer Systems, byPaul Goldsbrough, Trevor Lundand John Rayner; Howard W.Sams & Co.; 438 pages; $19.95paperback.

Analog electronics involved inthree basic building blocks of themicrocomputer system are pre-sented in this book that pullstogether a broad range of analogtopics and principles previouslyscattered among textbooks, notesand data books. The basic theoryand practical circuits of the analoginput subsystem, microcomputersubsystems and the power subsys-tem are presented clearly withample illustrations.

It isn't necessary to be a CET orengineer to use this bookeffectively, but a fair under-standing of digital electronics andmicrocomputing is recommended.

Howard W. Sams, 4300 W. 62nd St., In-dianapolis, IN 46268 toww,


Literaturevv\r_Wv

John Fluke ManufacturingCompany, announces availabilityof its 12 -page color brochure,Fluke DMM Accessories thatdetails the accessories producedfor use with this company's line ofdigital multimeters.

Several new products arefeatured, including the 80TK Ther-mocouple Module, which convertsvirtually any DMM into a digitalthermometer capable of both °Fand °C readouts. The 80TK plugsdirectly into a DMM, and uses in-terchangeable K -type thermo-couples for a wide variety oftemperature measurement ap-plications.

The brochure also includes fullcolor photos and detailed informa-tion on products designed for safe,precise measurement of highvoltage, high current, temperatureand high frequency. Convenienceaccessories such as carrying casesand test leads are also highlighted.


Topaz, Inc. announces theavailability of Solutions to PowerProblems, a convenient guide forselecting the correct Topaz PowerConditioning system for any sen-sitive equipment application.Topaz products protect computersand other electronic equipmentagainst electrical noise, voltagefluctuations and power outages.The product selection guidediscusses each of these powerdisturbances, identifies its causeand effect and offers effectivereference to the appropriate Topazsystem for each specific need.


AEMC Corporation has released a1985 supplement to its catalog ofportable test and measurement in-struments. The catalog covers ap-plications, specifications andordering information for new addi-tions to the product line, includinga 50V telephone line megohm-meter designed for conducting in-sulation tests on telephone in-stallations; the Bouncer II, a high -sensitivity analog multimeter in a

unique, resilient rubber housing;and the model 4500 digital groundtester, designed for measuringvery low resistance on largegrounding systems. Also featuredis the Multidisplay 2000, a unitthat accepts 13 AEMC Add -a -Function modules, and directlyrenders readings in the correctengineering units for variousparameters, including light, resist-ance, capacitance, frequency, andtemperature, depending on themodule used.


Complete information on thenew ESP Electronic ShortPathfinder is available to printedcircuit board manufacturers, labtechnicians, electronic circuitdesigners, electrical field servicepeople and others interested insaving up to 95% of troubleshoot-ing time and salvaging shorted PCboards. The brochure is offered byJ & L Information Systems. It in-cludes a complete explanation ofhow the ESP is operated, alongwith photographs and specifica-tions.


Choosing and installing the ap-propriate filter to cure terrestrialinterference (TI) in earth stationsis the subject of a catalog fromMicrowave Filter.

TVRO/85 contains descriptionsof MFC filters used to cure de-structive and non-destructive in-terference, as well as diagramsdepicting where filters should beplaced in the TVRO system.

Besides a variety of filtersdescribed in the catalog is the in-staller's kit, which contains filtersto diagnose and cure non-destructive TI in receivers with70MHz IF frequencies. The SkyDoc Kit, used to detect and cureboth destructive and non-destructive TI, is also included.


A catalog that features a line ofminiature precision soldering ironsand over 40 different inter-changeable, slide -on tips for elec-tronic assembly work is being of-fered by M.M. Newman.

The Antex Soldering Irons AndAccessories catalog is completewith product specifications.


Take the GuessworkOut of VCR ServiceTentel now has

3 products forquickly and easilydiagnosing themechanical perfor-mance of VCR's.TheTentelometertape tension gauge is the world stan-dard for tape tension measurementsto prevent skewing and interchangeproblems. The TSH gauge seriesfinds problems causing edge damageand binding cassettes, the two big-gest causes of tape destruction. TheNew HPG-1 head protrusion gaugerepresents a breakthrough for an ac-curate, easy to use method of deter-mining head life; takes theguesswork out of video head replace-ment. The HPG-1 for Beta, VHS, andU-matic VCR's measures head tipprotrusion and drum eccentricity inboth microns and ten thousandths ofan inch.

These 3 products allow the entiremechanical performance of a VCR tobe measured in a few minutes by onlyremoving the top cover of the VCR.

Call or write for details-We wantto hel

TENTEL (408) 379.18811508 Dell Avenue 8001538.8894Campbell CA 95008Telex 910 590 8001


FREE!New Catalog ofHard -To -FindPrecision Tools

Jensen's new catalog is jam-packedwith more than 2,000 quality items.Your single source for hard -to -findprecision tools used by electronictechnicians, scientists, engineers,schools, instrument mechanics,laboratories and government agen-cies. This popular catalog also con-tains Jensen's world-famous line ofmore than 40 tool kits. Call or writefor your free copy today!

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Readers' Exchangevvv Wv

For Sale: New B&K model 1805 multifunction counter with probe-features include frequency period, period average at totalize and 8 -digitLED display. Never used, with warranty and in original carton, $280 plusshipping and c.o.d. charges. Stanley Todorow, G8468 Belle Bluff Drive,Grand Blanc, MI 48489.

For Sale: Sencore VA62, NT64, CR70, LC53; B&K transistor tester. Allequipment has been pampered and is in excellent condition. Send s.a.s.e.S.G. Alfred, 1020 Ouichita, Carthage, TX 75633; 214-693-9204.

For Sale: Sencore VA48 with manuals, excellent condition, $680. SamsPhotofact folders, complete 900 to 1710, intermittent 62 to 2264, $1,200without file cabinets. 307-587-5251.

For Sale: Sams Photofact folders, 1,000 from 30 to 1600, $400, freightpaid; Sencore VA48, $350; Sencore Minuteman oscilloscope, $150; fre-quency counter, 100MHz, and CB tester, $90; B&K 5MHz oscilloscope,$75; Beltron picture tube restorer, $175. Send certified check. Dennis Han-ningstad, 928 King St., La Croase, WI 54601.

For Sale: B&K 1077B analyst, $200; Conar capacitance/resistanceanalyzer, $35; Weller soldering station, W-TCP-L, $35; Radio City flyback,yoke and capacitor tester, model 124, $40. All plus shipping. George C.Pullen, 6722 Botetourt Drive, Ft. Washington, MD 20744; 301-449-7348.

For Sale: Ham equipment- Kenwood TS -930S transceiver with AT -930automatic antenna tuner and CW filter, $1,300; Kenwood SM220 stationmonitor with BS -8 pan display, $275. William Shevtchuk, 1, Lois Avenue,Clifton, NJ 07014; 201-471-3798.

For Sale: Tuner rebuilders - quantities of tuners, sold only in assorted lotsof 10. Make offers. Troch's, 290 Main St., Spotswood, NJ 08884;201-251-3042.

Wanted: Used Futterman (Harvard Electronics) tube power amplifiers,either stereo or mono, working or non -working. Send price, address,phone, details including model number. Joseph Bagnata, Box 26, Harleigh,PA 18225.

Wanted: Operating manual and schematic for Hewlett Packardoscilloscope, dual trace model 180A. Will pay for copying or will copy andreturn. John Kosa II, Route 1, Box 66B, Red House, WV 25168.

For Sale: B&K 2040 CB signal generator, B&K 1040 CB Service Master,129 Sams CB Photofact folders, $500 for all. Meade TV & Electronics,502e/s First Ave.. West Logan. WV 25601.

For Sale: Soar dual trace oscilloscope, model MS -6023, with probes andbuilt-in DMM, used one year, $400, or best offer; HP85B computer withmemory module, software and manuals, $1,250. Mark Vuozzo, 17632 Jor-dan, No. 38B, Irvine, CA 92715; 714-788-0872.

Wanted: Sams S D manuals, 1 through 5 and 7 through 13. Please sendprice, including shipping. Paul A. Todd, Box 54, Alton Bay, NH 03810;603-875-3772.

Wanted: Sanyo 31C36 tuner escutcheon panel (P/N 111-0-1220-24100, cont. Dec.). Also battery holder for 10 AA batteries in two rows offive for Lafayette transceiver model Dyna-Com 3B. Larry Cope, 1612Serenity Lane, Sanibel, FL 33957.

Needed: Picture tube, used but good condition, type 15VAETC01. Also in-formation on théory and repair of remote control units on color TV sets,preferably RCA. James E. Gregorich, 117 -2nd St. North, Virginia, MN55792; 218-749-4355.

Wanted: Disabled man on limited income needs a tube tester, CRTtester/rejuvenator, transistor tester and capacitor tester at prices that canbe afforded, or payments arranged. Edward Gordon, 2627 HammontonRoad, Marysville, CA 95901; 916-742-9195.

For Sale: Vibrators, Bradford TV manuals, complete Western Auto TVmanuals, many Sams AR, TSM, MHF manuals. Make offer. Osceola Elec-tronics, 226 S. M66 Highway, Marion, MI 49665.

For Sale: Sams Photofact folders 1 to 2312 in 4 -drawer file cabinets, 69AR, TSM, MHF manuals, also Delco radio manuals. All for $2.200. TedSmith, Box 706, Sophia, WV 25921; 304-683-5677.

For Sale: Sencore VA62 universal video analyzer, Sencore VC63 VCR testaccessory, Sencore NT64 (NTSC-EIA) pattern generator, Sencore CR70universal CRT analyzer and restorer. All for $2,800. Alan Smith, Box 1885,Sophia, WV 25921; 304-688-5677.

For Sale: Oscilloscope, Hitachi model V-352, 2 -channel, dual waveform,35MHz, $550; B&K Precision 3010 function generator, $150; TF46 port-able Super Cricket transistor/FET tester-won in contest, never used,$350. Derrick Wallace, 186 E. Mercury Blvd., Hampton, VA 23669.

For Sale: Thordarson - variety of horizontal transformers, mostly color,some b&w, high voltage, $15 each, plus shipping. Variety of oddball tubes,metal 6L6, for example. Send s.a.s.e. for details. Other TV and stereoparts. Boyd Hawks TV Service, Route 8, Box 18, Galax, VA 24388;708-286-4210.

Wanted: EICO model 460 oscilloscope with good power transformer. Orwill sell defective EICO with new NEC CRT C529P31B (CRT used only afew times). Ernie, P.O. Box 122, Elgin, OR 97827; 508-437-5971.

For Sale: Sencore VA48, used only once, complete with instructions and inoriginal box. Make offer. William J. Maida, 247 W. Sabal Palm Place,Longwood, FL 32779.

For Sale: All copies of P.F. Reporter and Electronic Servicing &Technology, 1964 through 1975, and 1980 through 1984, 50 cents per copyplus shipping. Lloyd E. O'Brien Sr., P.O. Box 105, Springfield, WV 26763.

For Sale: New parts-Zenith color yoke 95-2638, B&W yoke S94147-01,vertical transformer 95-2851, color yoke Y108 952286; Admiral color fly311 79D126-1; Magnavox color fly 574 361520-2; each part $20, $100 forall. Tony Gonzales, 1605 S. 56th Court, Cicero, IL 60650; 312-652-8454.

For Sale: Heathkit IM -48 audio analyzer, never used, $50; IB-58 harmonicdistortion meter, never used, $70 or best offer. Add shipping. C. England,98 Montague Ave., South Zanesville, OH 43701.

For Sale: Teletype model 33ASR machines (two), asking $90 each, with orwithout stands. D. Testa, P.O. Box 9064 EST, North Newark, NJ 07104.

For Sale or Trade: 300 Sams Photofact folders, assorted 121 to 1,000;pre -1970 manufacturers' service information on radios and televisions; oldtest equipment. Frank Moon, Route 3, Box 355A, Alexander City, AL 35010;205-839-6965.

For Sale: Back issues of Electronic Servicing & Technology dating from1966 and Radio Electronics from 1952. Make offer for all. M.R. Easterday,6809 W. 100, Overland Park, KS 66212.

For Sale: Hickok tube tester model 510X with schematic, instructions andtube chart (needs line cord) $25 as is; B&K tube tester model 707 Dyna-Jet$75 as is; B&K Precision Tube Master series 10 to 12 tube and batterytester, with roll chart, in wood dovetail box, working order, $100. Payablein U.S. funds plus postage, M.O. only, no checks. Ed Barlow, Box 29,Tweed, Ontario, Canada KOK 3J0.

For Sale: Bound copies of Electronic Technology with Tekfax, 1960 to1980, best offer; Hickok model 610A universal TV alignment signalgenerator, manual, cable, etc., $50 plus shipping. M.B. Lindenaux, 15Marlin Drive, New Port Richey, FL 33552; 813-842-4818.

Needed: Schematic and service information for Panasonic model PVA500VCR tuner, used with a PV -5000 VCR. Will pay for any copying costs. JeffParker, 7901 Twin Oak Court, Raleigh, NC 27609.

For Sale: Beitmain TV books, 1947 through 1970, $60 for all; Sams ARs,$3 each. Wanted: Sams AR170, 243, 262, 266, 292, 293, 299 and 300; tube -type TV sound tuners; SECO HC6 cathode checkers. Jim Farago, P.O. Box65701, St. Paul, MN 55165.

For Sale: Heathkit digital multimeter IM -2260, with ac adapter and Ni-Cdbatteries, excellent condition, $95, including shipping. Calvin Logue Jr.,17J Washington Lane, Westminster, MD 21157.

Wanted: Will any technician who might be using the Dandy (manufacturer)color CRT kit intended for use on any model of B&K (and others) 440 orB&K 465 please write. I will compensate you for your trouble. Thanks,Joseph A. Gontarz, 14 Rudolph Road, Forestville, C7', 203-583-7532.

For Sale: RCA Senior Voltohmyst with new VIZ meter movement modelWV -98A, will include Simpson 260 multimeter that needs minor repairs,$100 or best offer. Gary H. Thompson, 3648 Eastside Highway No. 5,Stevensville, MT 59870.

Wanted: Test Equipment-Leader LCG400M generator; Leader,Tektronix, Hewlett-Packard or Sencore oscilloscopes with 60 to 100MHz,alt. time base and intensifier with calibrated delay; Sencore VA62 withNTSC and VCR accessory. Send offers. Miller TV, P.O. Box 364, Portales,NM 88130; 505-356-4207.


For Sale: Sams transistor service manuals TSM 1 through 139 (137 and138 missing), $1.50 each or $150 for all, plus shipping; Sama Photofactfolders 36 through 496, some missing, $1 each or 348 total for $300 plusshipping; Sams tape recorder service manuals TR1 through TR4 and TR11;Sams record changer service manuals CM -2 through CM -9, RC -11 andRC -12, $3 each or all 15 manuals for $30 plus shipping. Call or send s.a.s.e.for complete list. Also, Philco wideband oscilloscope amplifier model 8300,good condition, $15. John Brouzakis, R.D. 3, Box 602B, Charleroi, PA15022; 412-488-3072.

Wanted: Schematic for Cordovex electronic piano by Elex, model PP23.Gregg Titles, Route 1, Box 87L, Staunton, VA 24401.

For Sale: Sencore CG22 color -bar generator, $65; Sencore AT218 IF at-tenuator, $20; Sencore TR219 horizontal output drive isolationtransformer, $25. All, excellent condition. Elmer Wieland, 237 TalbotDrive, Bedford, OH 44146; 216-232-8653.

For Sale: Sencore S6165 AM -FM -stereo analyzer, complete, $475. ValObal, 3201 S. 73rd St., Omaha, NE 68124; 402-393-0459.

Wanted: New or used third video IF transformer for RCA TV model CTC-24A-Sams 912-3, RCA part No. 116544 (also used in CTC-31 and othermodels). R.N. Baughman, 572 Strumbly Drive, Highland Heights, OH44143.

Wanted: NRI TV, video servicing courses and equipment; NRI computerand microprocessor courses, equipment and computer. Reasonably priced.Joseph Wegner Jr., P.O. Box 262, Glendale, CA 91209.

For Sale: Heath post marker sweep generator model IG-57-A, like new,with instructions; Pace capacity and resistor checker with instructions.Make offer. William J. Maida, 274 W. Sabal Palm Place, Longwood, FL32779.

For Sale: B&K 80MHz multifunction counter model 1805 featuring fre-quency, period, period average, 8 -digit LED and other specifics, new,never been used, $290 includes xl/x10 probe. New, never been used Flukemodel 27 DMM with features that include 0.1% do accuracy, min/maxrecording, relative mode, bar graph, conductance and others, $230. Pricesplus shipping, insurance and c.o.d. charges. Cathy Johnson, 72 Mary Staf-ford Lane, Flint, MI 48507.

For Sale: Rider service manuals, volumes 4 through 16, 19, 20, 27 and 28,$15 each. Sams Photofact folders, bound. Folders per binder vary innumber: Nos. 31 through 48, 61 through 500, 512 through 557, 578through 616. Priced $2 per folder x number of folders per binder. Sends.a.s.e. with your requirements for quotation. Folders will not be can-nibalized. E.E. Pitsinger, Unitronix, P.O. Box 247, Galveston, TX 77553;409-763-2207.

Wanted: Schematic and manual for AKAI reel-to-reel tape recorder model4000D, serial No. 70111-00266. Will pay for information. Lloyd Spivey,WLLS AM/FM, Spinks Shopping Center, Hartford, KY 42347;502-298-3268.

For Sale: Sencore VA48 video analyzer in original box, $675; Sencore Zmeter LC53 with 39G85 Touch Test probe and SCR224 TRIAC test ac-cessory, $585; Heathkit 10-4101 vectorscope and pattern generator, $55;Heathkit IT -5250 color CRT tester and rejuvenator, $40; EICO 242 solid-state FET TVOM lab meter, $25. Cash only. R.M. Hoffineyer, 1170 PinoSolo Drive, Santa Maria, CA 93455; 805-937-4073.

Wanted: Knight 83YX137 AF generator and RF generator with manuals;83Y135 signal tracer manual. C.T. Huth, 229 Melmore St., Tiffin, OH44883.

Needed: Schematic for Thomas organ No. 101021, year approximately1962. Elmer's TV, 437A Pearl Ave., Monrovia, CA 91016.

Wanted: For VCR repairs -tape tension and spindle gauge, video testtape, etc. Also, Panasonic 12 -inch picture tube No. A26JAS31X. EdHerbert, 410 N. Third St., Minersville, PA 17954.

For Sale: B&K Precision 3020 sweep function generator, like new,$250; B&K Precision No. 1420 oscilloscope with probes and demodulatorprobe, like new, $595 or best offer. Vandy's, 5306 N. Magnet Ave., Chicago,IL 60630; 312-775-5497.

Wanted: Sencore SC61 PR57. Lewis TV, 326 Main St., Huntington Beach,CA 92648; 714-536-3715, after 1 p.m.

Wanted: A set of back issues of ELECTRONIC SERVICING &TECHNOLOGY dated to October 1984. Please state price including ship-ping. Lyle Estabrook, 2365 SE Sedgwick Road, Port Orchard, WA 98366.

Advertising rates in the Classified Section are 75cents per word, each insertion, and must be accom-panied by payment to insure publications.

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FOR SALEAUTOMOBILE RADIO and tape replacement parts.Delco, Chrysler, Philco-Ford, Motorola, Panasonic andmany others. Large inventory. Laran Electronics, Inc.,3768 Boston Road, Bronx, NY 10469. (212) 881-9600.National (800) 223-8314, NY State (800) 446.4430.

1-85-tfn

BOOTLEGGERS BIBLE for CB Modification $12.95, CBRadio Repair $10.95. Linear Amplifier Planbook$14.95, kits, etc. Catalog $1.00 refundable-APS, POB263 Newport, R.I.02840 401.846-5627. 12-84-tfn

SCRAMBLED TELEVISION, encoding/decoding. Newbook. Theory/circuits, $9.95 plus $1 shipping. Work-shop, Box 393ES, Dept. E, Bethpage, NY 11714.

1-85-tfn

TV TROUBLE ANALYSIS TIPS. Over 300 symptoms/remedies by circuit area; tough ones over the years.Save time and money. Send $12.50 to CHAN TV, 8151Grandview Rd., Chanhassen, MN 55317. 1-85-tfn

MAKE TELEPHONE answering machine servicingsimple & professional. Without tying up your phonelines, our ring simulator will activate any machine onthe market. You can hear the outgoing message, giveyour message, and also have the availability to checkmachines that have remote capability. Send yourcheck for $85.00 made payable to PSI, INC, to covercost of machine shipping and handling or call (201)845-6669. PSI, Inc. is located at: 34, Route 17 North,Paramus, New Jersey 07652. 4-84-tfn

CABLE CONVERTERS. Lowest price. Dealer inquiriesaccepted. Quantity Discounts. FREE CATALOG. P.G.Video Corp, 61 Gatchell St., Dept. ES&T, Buffalo, NY14212. 5-85-tfn

FOR SALE TALK A PHONE, 4-KLR 2M 35.00 each;1- KLR 2L 25.00; 1- KHP 3 50.00; 1-K CL 5 125.00;1-K-LR-2M 35.00; 3 -K -AC -610 175.00; 2 -TLS 10150.00; 1- K -C-41 M 50.00; 1- K -S-100 80.00;1 -K-S-101 80.00; 1-K-SM 7.00; 1 -K-SM-L 7.00; 1 -HI -9R -1 100.00; 1 -HI 4 30.00; 1 -Hl -8 75.00. Gerald Cooper,P.O. Box 500, Hagerstown, Md. 21741. 1-861t

REPAIR OF ZENITH circuit board 9.160 -all; with dudexchange $33.00. One year guarantee. Kinirral Elec-tronics, 68-26 64th Place, Glendale, N.Y. 11385, (718)388-3859. 12-8-5-3t

COLOR T.V. REPAIRS, OVER 3,000 TIPS on 31 brands,116 page manual. Send $21.00, A.F. Fernandez, Box546110, Surfside, Florida 33154. 1-86.1t

SANYO HORIZONTAL OUTPUT TRANSISTOR2SD1341, $1.99 plus other name brand transistors,IC's, RF-Power, Sanyo rechargeable batteries andLED's. For best buys plus service call 1-800-458-6053.PA call 1-800-672-7100. M/CNISA honored. Savings,service, quality. At B&D we do it better. B&D Enter -prizes, Box 305, Kane, PA 16735. 1-86-2t

SONY-TRINITRON REBUILTS are now available. Callfor price & delivery, 1.716.621-5250. 1-86-2t

CABLE TV CONVERTERS & EQUIPMENT. Plans andparts. Build or buy. FREE information. C&D Elec-tronics, P.O. Box 1402, Dept ES&T, Hope, Arkansas71801. 1-86-tfn

INDIVIDUAL PHOTOFACT FOLDERS (Not sets) el to#1400. $3.00 first-class postpaid. Loeb, 414 ChestnutLane, East Meadow, NY 11554. 1-86-3t

SENCORE V.A. 48 like new. Includes all leads &manuals. Must sell. $750 or best offer. 707-443-6820.

1.86.11

WANTED TO BUY

WANTED: To buy well established TV -video repairshop in Brooklyn or Manhattan Boroughs of New York.Please Call: (718)336-9573. 1.86-1 t

HELP WANTEDCAMERA -VIDEO Technicians needed. Top pay andbenefits for well trained and experienced technicianswho are expert with consumer and/or industrialcameras and VCR's. Training by manufacturers suchas Sony, Hitachi, Panasonic, etc., are necessary forjob experience. Come to sunny Florida and enjoy yourwork & leisure time. Write or call ATLANTIC ELEC-TRONICS INC., 1881 NE 26 St., Ft. Lauderdale, FL33305. (305) 564-827410 AM to 6:30 PM. Ask for Dave orJoe. 8-85-tfn

WORK IN TAX FREE CARIBBEAN: Senior Tech/SvcManager for Electronic facility. Applicant must becapable of repairing TV, VCR, Audio Etc., and possessrelevant certificates. Shop consists of Security,Satellite, 2 -Way, Paging and Mobile Telephonebusiness. Excellent equipped shop with good workingconditions. Salary negotiable. Submit Resume to:Manager, 660 S.W. 63rd Court, Miami, Florida 33144.

1.86-1t


HELP WANTED (CONT.)

TV TECHNICIAN - Fully trained and experienced inTV -VCR -Repair. Top pay & benefits. Located on theeastern shore of Maryland. Send resume to Techni-cian, P.O. Box 269, Pocomoke, MD 21851. 1-86-1t

BUSINESS OPPORTUNITIESCOLORADO. Established Television Sales and Ser-vice, southeast Denver. Authorized Sony, RCA, Zenith,Magnavox, (303) 741-3483. 12-85-2t

3 HOURS FROM SAN FRANCISCO! Town of paradisein pine forested foothills. Electronic repair business.Building/shop/equipment/7 room resident with largegarden. $165K, (916) 872-1962. 12-85-t f n

SELF DESIGNERS, Investors, and Electro-Hobbistswe offer you our Complete Home Robot Designs. Ex-clusively from Cad Design Services. For your manual,and listings of other current designs, send a check ormoney order for $5.00 to: CAD Design Services, P.O.Box 1192, Jackson, MI 49204. 1-86-2t

TV SALES AND SERVICE BUSINESS in boomingtourist area, on the lakes. Must sell - moving. Equip-ment, parts inventory, service literature and van. Havegood business with good reputation. Located in goodshopping center. Asking $12,000. Square Deal TV, For-syth, Mo. Phone 417-546-2262. 1-86.1t

T.V. SALE & SERVICE FOR SALE in L.A. area, Califor-nia. Inventory includes 63 VAN 77 Lincoln Cont. Gross$50.000. Low rent. 10 yrs. established, asking $30,000.Ray Garcia. 13051 Woodcock, Sylmar, CA 91342.

1-86-1t

TV REPAIR BUSINESS: Excellent income. Great futurefor ambitious individual with electronic skills. S.R.QUINN & ASSOC., (215) 576-1372. 1-86-1t

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DANDY-DAPTER'PATENTED CRT ADAPTER - Don't buy another socket for yourCRT Tester! This is the Only way you can win the SocketWar! Guaranteed to fit your tester & allowyou to test/clean/restore ANY Color.B/W. Projection. Scope or Camera CRTs.Visa/M-Card. Checks. CODs. New LowPrice $59.95 (We pay UPS) 1(800)331-9658. DANDY ELECTRONICS. 2323GIBSON, MUSKOGEE, OK 74403.


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Go for 'em! Solid margins year -around! They're yours in thevideo aftermarket! With this new VCR Care Kit by Zenith!

You bet there's a VCR aftermarket out there! A sizeable one. Perhapsas big as twenty million plus households. So that capitalizing onit with VCR accessories like this beautifully packaged Zenith VCRCare Kit can be very, very profitable.

Look and see for yourself!

Inside this kit, latest in a long line of Zenith video accessories -and available separately, too - are a great new VCR Head Cleaner.A T-120 VHS Blank Video Tape. A VCR Dust Cover. And a clear VHSTape Storage Cover. All proudly bearing and backed by Zenith, aname renowned for superb product performance and reliability.

They are at your Zenith distributor's place now,these new Universal VCR Care Kits, readyfor immediate delivery to heads -upservice techs alert to the moneyto be made in the overallvideo aftermarket.

Actually, there's more in store than ever before in this expandingline of Zenith video accessories. More than just this new Universal

VHS VCR Care Kit. Solid margins, for example. The kind that canturn some 6, 7 or 8 feet of your floor space into a video accessory

profit center right before your eyes.

So hurry! Quit second-guessing yourself! Neither this videoaccessory business nor VCR aftermarket is going to wait for you.

Call your Zenith distributor's Parts & Accessories Sales Manager!

Besides being an integral part of Zenith's newVCR Care Kit, this VCR Head Cleaner

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