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or DC: minus or plus; and low battery.THINK OF USE.Easy -to -use range and functionswitches help avoid errors. Jacks orstandard 3/4" dual plug centers. Unitcomes with tilt stand, deluxe probesand batteries. H.V. probe, AC adapter,LED continuity probe and carryingcase, optional.

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Electronic Servicing

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

EDITORIALBill Rhodes, Editorial DirectorCarl Babcoke, Consumer Servicing ConsultantRhonda Wickham, Managing EditorLynn Chamberlain. Associate Editor

ARTDudley Rose, Art Director

CIRCULATIONJohn C. Arnst, DirectorEvelyn Rogers, ManagerDee Marues, Reader Correspondent

ADMINISTRATIONR. J. Hancock, PresidentCameron Bishop, Publisher

ADVERTISINGGreg Garrison, National Sales ManagerMary Birnbaum. Production ManagerMark Raduziner, Marketing Coordinator

Regional advertising sales offices listed nearAdvertisers' Index.

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ELECTRONIC SERVICING (USPS 462-050) (with which iscombined PF Repcder) is published monthly by IntertecPublishing Corp , P 0 Box 12901, 9221 Ouivira Road.Overland Park, KS 66212 Second Class Postage paid atShawnee Mission. KS 66201 Send Form 3579 to P 0 Box12901, Overland Park. KS 66212

ELECTRONIC SERVICING is edited for technicians whorepair home -entertainment electronic equipment (such asTV. radio. tape. stereo and record players) and for in-dustrial technicians who repair defective production -linemerchandise, test equipment. or industrial controls in fac-tories

Subscription prices to qualified subscribers one year $12.two years $19, three years $24 in the USA and its posses-sions Foreign countries one year $17. two years $27.three years $35 Subscription prices to all others one year$25. two years $50 in the USA and Its possessionsForeign countries one year $36. two years $72 Singlecopy price $2 25 back copies $3 00 Adjustmentnecessitated by subscription termination to single copyrate Allow 6 to 8 weeks delivery for change of addressAllow 6 to 8 weeks 'or new subscriptionsPHOTOCOPY RIGHTS: Permission to photocopy for internalor personal use is granted by Intertec Publishing Corp forI braves and other registered with Copyright ClearanceCenter (CCC). provided the base tee of $2 per copy of arti-cle is paid directly to CCC. 21 Congress St Salem. MA01970 Special requests should be addressed to Camero-Bishop. publisherISSN 0013-497X/81 $2

ICSINTERTEC PUBLISHING CORP.

1981 All rights reserved.

Easilythe best.In terms of resolution andaccuracy, the Model 135is easily the best handheldDMM available at anyprice. It's the onlyhandheld offering 41/2digits. That gives it 10times better resoultionthan the best 31/2 -digit

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accuracy. Resolution isn'tall you get. You get aneasy -to -use instrument that'srugged and reliable enoughto live in the read world.You get Keithley packaging.

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make it easy to use. Once -a -year calibration and long batterylife make it easy to own. Easy to uy at '235.

Best in price, best in performance.There is a DMM designed specifically for your application in the Keithleyline. Your Keithley distributor has instruments in stock for yourconvenience. Call today for complete information and a demonstration.

Sound Choice.New Model 128 Beeper DMM.Audible/visual indication on all5 functions of this 3'/2 -digitDMM lets you test faster, andthe user adjustable threshold andspecial diode test function makeit a sound choice. Uniquefeatures, '139.

Bench Bargain.Model 176, Portable Bench DMM.Full 5 -function LCD 4'/o -digitbench DMM offers 0.05% basicDCV accuracy. Keithley ease ofuse features include range andfunction annunciators, 1000hour battery life and optionalline operation. A bargain at '269.

KEITH LEYKeithley Instruments, Inc.28775 Aurora Road/Cleveland, Ohio 44139/(216) 248-0400

Circle (2) on Reply Card

September 1981 Electronic Servicing 1

For industrial maintenance and consumer servicing professionals

Electronic ServicingSeptember 1981 Volume 31, No. 9

Features 6 Servicing videodisc equipmentBy Kirk VistainThe popularity of videodiscs andvideodisc players brings a valuableopportunity to those technicians whoprepare for it.

16 Semiconductor source guideA look at semiconductor replacementparts catalogs.

20 Servicing shutdown circuitsBy Homer L. DavidsonTroubleshooting color receiverscontaining shutdown or hold-downprotective circuits.

28 Zenith power and horizontalsweep, part 1By Carl Babcoke, CETExploring the unique circuit thatregulates the Zenith horizontal sweepand all scan -rectified power supplieson the M10 module.

38 Understanding digital ICsBy Gene Turchin

Departments 3 People5 Scanner

37 Symcure

42 Product report43 Photofacts43 Reader's exchange

About the cover This integrated circuit, a Harris 16K CMOS random ac-cess memory chip (enlarged 50 times) contains 100,000circuit elements including transistors and other com-ponents. (Photo courtesy of Harris Corporation)

Copyright. 1981, by Intertec Publishing Corporation All rights reserved Material may notbe reproduced or photocopied In any form without written permission of publisher

2 Electronic Servicing September 1981

O it in the news

George Savage, CET, ofDoniphan, NE, became ETA's thirdchairman as the associationcompleted its annual conventionJuly 12, 1981, at Iowa StateUniversity in Ames, IA.

Savage, married and the father offour teenagers, has served as vicechairman and secretary of ETA inaddition to being membershipchairman for two years. He wasinstrumental in establishing a localchapter of ETA in central Nebraskaand has participated in theassociation's technical trainingseminars on several occasions bylecturing on improved troubleshoot-ing methods.

Savage has a long career as anelectronics technician and servicemanager in the consumer electronicsfield. Recently he switched to theindustrial area and is now serving asan engineering technician for theInternational Sensor Corporation,located in Aurora, NE. Internation-al Sensor produces integrated cir-cuits and MSI chips.

Industry veteran Herb Horowitzhas been named president of Rotelof America. Founder and formerpresident of Empire Scientific,Horowitz also has served as presi-dent of the Institute of High Fideli-ty, Ortofon USA, as special projectsdirector for Harman Internationaland, most recently, as executive vicepresident of Acoustic Research.

Lam Research Corporation hasnamed Adrian "Bick" Hohn its na-tional sales manager, a new posi-tion. Hohn will report to Dr. DavidK. Lam, president.

Hohn brings more than 15 yearsof direct sales and sales manage-ment experience to his new post.Prior to joining Lam Research, hemanaged western regional sales forCobilt (now a division of AppliedMaterials).

Hohn's sales experience substan-tially relates to semiconductor pro-duction equipment and materials.Besides his 3 -year tenure with Cobilt(alignment/exposure systems), he

has served in sales positions withThermco (diffusion furnaces) andApplied Materials (wafer processsystems).

Charles R. Stoyer, senior productspecialist, has been promoted toproduct manager, customer tooling,for ITT Cannon Electric. Stoyerjoined this division of InternationalTelephone and Telegraph Corpora-tion in 1976 as field -based productspecialist for the east coast.Previously, Stoyer worked forAMP, Inc., and Moore BusinessForms, both of Harrisburg, Penn-sylvania.

The Regency Electronics Inc.,board of directors has elected Floyd0. Ritter as chairman of the boardand chief executive officer, andJoseph E. Boone as president andchief operating officer. Ritter wasformerly president and Boone wasexecutive vice-president.

Edwin J. Sommer, who had beenboard chairman, will continue as acompany director.

Shure Brothers Inc., Evanston,IL, has announced the promotion ofRobert B. Schulein to chiefdevelopment engineer and head ofthe company's ElectromechanicalDevelopment Department.

Schulein joined Shure in 1966.His previous position was chiefdevelopment engineer -acoustics.

Audrey Griffin has been appoint-ed executive producer for VHDPrograms Inc., Los Angeles, CA,the company that is launching VHD(video high density) videodiscs inthe United States. She is responsiblefor working with outside producersto create participatory andentertainment programming, andwill report to Paul B. Foster, vicepresident of program development.

Most recently Griffin was directorof special programs for RCASelectaVision Disc, working indevelopment and acquisition ofgeneral audience programming.

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The rugged 1420 features dual -traceoperation and an honest 15MHz re-sponse, with useful response beyond20MHz. An efficient rectangular CRTdisplays waveforms with good read-ability under all field service conditions.

There is no sacrifice of features orperformance for compact size. The 1420has 18 sweep ranges from 1µS/div. to0.5S/div. in a 1-2-5 sequence; variablebetween ranges. Sweep magnificationis X10, extending the maximum sweeprate to 100nS/div. For use with computerterminals or video circuits, a video syncseparator is built in. Automatic selectionof chop and alternate sweep modes isprovided, as is front -panel X -Y operation.

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Circle (3) on Reply CardSeptember 1981 Electronic Servicing 3

electronic METTE

New York judge rules onrepair shop inspections

Relying upon a series of UnitedStates Supreme Court holdings, aState Supreme Court justice has de-clared unconstitutional a New YorkCity law authorizing warrantless in-spections of radio and televisionshops licensed by the Department ofConsumer Affairs, according to theNew York Law Journal, June 9,1981.

Justice Anthony T. Jordan, in atest case brought by a televisiondealers trade association, ruled thatwithout the consent of a shop'sowner, the inspectors could not de-mand entry to books and recordsunless they had obtained warrantsand provided written notice beforethe date of the inspection.

Jordan issued his findings in Mat-ter of Glenwood TV Inc. (Ratner) adecision filed recently in KingsCounty, Supreme Court, SpecialTerm, Part 1, in which he orderedthe department to reinstate thelicenses of two shops suspendedwhen they refused to permit inspec-tors to see their records. The re-quirements for a warrant dealt onlywith routine annual inspections, notwith cases where there has been acomplaint or some emergency situa-tion.

The justice based his ruling upona number of Supreme Court deci-sions which voided warrantlesssearches of residences or regulatedbusiness, with specific exceptionsthat he found did not apply to thematter before him, such as closelyregulated industries or those subjectto "pervasive regulations." Thesebusinesses were liquor stores orfirearms dealers.

Also cited was the recent HighCourt ruling that barred warrantlessinspections by inspectors under theOccupational Safety and Health Actof 1970 unless they were carried out"in a manner that satisfies theFourth Amendment."

"With none of the above -enumerated exceptions being ap-plicable," Justice Jordan wrote, "thecourt must conclude that therespondent had no constitutional

authority to conduct a warrantlessinspection of the petitioners'premises or penalize the petitionersfor their refusal to allow such in-spection.

"Sections B32-472.0, subd. 5, and773-13.0 of the New York City Ad-ministrative Code . . . are thereforeunconstitutional insofar as they pur-port to authorize periodic inspec-tions of the type involved hereinwithout a search warrant. . ."

It was at this point that the courtlaid down standards for inspectorsto follow in conducting"reasonable" inspections. They in-cluded written notice of at least aweek before an inspection wasplanned, with the repair shop ownerbeing advised of the purpose and "adescription of the things to be in-spected," given an opportunity toarrange "a more convenientappointment" and alerted that theowner had the right to "insist upon asearch warrant before any inspec-tion."

Hipot tests savelives, property

Fires and electrical shock haveresulted from failure to spend a fewseconds making an electrical leakagetest of repaired audio-visual equip-ment, according to the Associationof Audio Visual Technicians.

The association warns that skimp-ing on the simple high potential or"hipot" test can result in serioushazards to users of AV equipmentand damage the reputation of repairtechnicians.

"Even though an equipmentrepair has nothing to do with theelectrical circuitry the test should beperformed because of the possibilityof a pinched wire, rearrangement ofparts, or even an undetected prob-lem present before the repair," saysElsa Kaiser, executive director ofthe association.

The principle of a hipot test is toprovide more than normal voltageto the equipment, to be as certain aspossible there will be no hazard innormal operation. Before the hipottest is performed, check for elec-

trical continuity between the groundof the 3 -wire plug and the metal caseor mechanism plate of the equip-ment. Use a simple continuity lightor ohmmeter to do this. Thereshould be continuity. If the equip-ment has a 2 -wire cord, the ground-ing wire from a dielectric tester is at-tached to the metal case ormechanism.

To make the hipot test, the dielec-tric tester is connected to an or-dinary electrical outlet, and the unitbeing tested is connected to it. Forsafety's sake, it is important that theservice technician not touch theequipment while the high potentialis being applied.

Generally a satisfactory test forAV equipment is to apply 600VRMS for 10 seconds to the line -voltage wiring. During the 10seconds, the leakage current shouldbe no more than 2.5mA (0.0025 A).Greater leakage current may in-dicate a short, breakdown of insula-tion, damaged components, orother problems which should be cor-rected before the equipment is re-turned to use.

1982 Winter CESbound for success

Applications for space in the 1982Winter Consumer ElectronicsShow, January 1-10, indicate that itwill be the largest ever, with manymajor 1981 WCES exhibitors re-questing increased space and morethan 100 companies exhibiting forthe first time.

This increased demand will be ac-commodated by utilizing the 40,000square feet of new exhibit space inthe Las Vegas Convention Center,bringing the show's total size tomore than 500,000 net square feetwith a potential of 900 exhibitors.

"We attribute this strong supportfor the show," said Jack Wayman,senior vice president of EIA/Con-sumer Electronics Group, sponsorand producer of the Consumer Elec-tronics Shows, "to a combination offactors, namely: The rapid growth of technologyin consumer electronics, as evi-


denced by the hundreds of newproducts that will be introduced atthe show. The changing patterns of distribu-tion that result from the new marketneeds in all product categories inconsumer electronics. The importance of Las Vegas as alocation that attracts many from theWestern U.S. who do not always at-tend the SCES in Chicago. The show becoming an importantinternational event for companieswho market their products world-wide. Use of the show as a vital forumfor manufacturers' sales meetings,the establishment of sales quotas,new promotions and merchandisingtechniques.

"Obviously, the 1982 WCESsatisfies the needs of our industry,"Wayman said.

In conjunction with the show, theNational Association of RetailDealers of America (NARDA), theindustry's retailer group, will holdits annual convention.

EIA conferenceset for October 19.20

The Electronic Industries Asso-

ciation's 57th annual Fall con-ference will be held Oct. 19-21,1981, at the Fairmont Hotel in SanFrancisco, CA.

Included in the tentative scheduleis a meeting of the Antennas,Towers and Accessories Committee,the Electronic Industries Founda-tion Board of Trustees, the caraudio subdivision, and the AudioDivision Board of Directors. Aspouses program is also available.

In addition, a symposium, "TheDOD Electronics Market - Impactof the Administration," sponsoredby the Government Division's Re-quirement Committee, will be heldOct. 27-29, 1981, Hyatt on UnionSquare, in San Francisco.

Conferences scheduled for 1982include the EIA Spring conferenceMarch 29 -April 1, at the ShorehamHotel in Washington, D.C., and theFall conference, scheduled for Oct.11-13 at the Century Plaza Hotel inLos Angeles.

Video products sales surgeTotal U.S. market sales to

retailers of major consumer video

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This space contributedby the publisher

products-color and monochromeTV receivers and videocassetterecorders - increased substantiallyin the first half of 1981, comparedto the same period last year.

According to industry figurescompiled by the Marketing ServicesDepartment of the Electronic In-dustries Association's ConsumerElectronics Group, color TV sales inthe first six months increased by20.3%, monochrome TV was aheadby 13.4% and first half video-cassette recorder sales gained by89.6% over the first half a year ago.

Sales to retailers of color TV setsin the 26 weeks, year-to-date, roseto 5,143,615 units, up 20.3% over4,275,463 units sold in the first halflast year. Color television receiversales in June 1981 amounted to1,007,584 units, up 8.9% over925,187 units sold in the samemonth a year ago.

Videocassette recorders (VCR)sales in the first half of 1981 climbedto 543.473 units, an increase of89.6% over 286,601 units sold in thefirst half of 1980. Sales of VCRs inJune jumped to 109,375 units, again of 110% over 52,076 units soldin the same month a year ago. 0

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Newest Magnavislon videodisc player from Magnavox is equipped with a wireless remote control unit.

The popularity of videodiscs andvideodisc players is beginning, andthis brings a valuable opportunity tothose technicians who prepare for itby learning the circuits and repairtechniques

Videodisc players probably willbe the next home -entertainmentelectronics product to enjoy tremen-dous sales acceptance from TVviewers. All these players are design-ed to be viewed on standard B&Wor color TV receivers.

Magnavox offered the first laser -optical videodiscs and videodiscMayers on an extremely limitedbasis (one city) in December 1978.Distribution increased gradually un-til it covered all major areas of theUnited States. The supply ofMagnavox machines and videodiscs,however, remains tight in manycities.

Pioneer markets a similar optical

videodisc player under its VP -1000model number, with most sales ap-parently made in audio -specialtystores. Kenwood and Gold Star alsohave exhibited similar compatibleoptical videodisc players.

In late 1980, RCA released theSFT-100 videodisc player and avariety of discs for its Capacitance -Electronic Disc (CED) type ofmachine. Several years of engineer-ing development preceded the CEDsystem. Zenith now markets asimilar machine, while RadioShack, Sony. Hitachi and othershave announced that they willemploy the CED system. CEDmachines have grooves and a stylus.

A third videodisc system awaitingintroduction is the JVC Video HighDensity (VHD) machine, whichoperates on a capacitance signal -pickup principle without grooves.General Electric, Panasonic,Quasar, Thorn EMI, Sansui andHitachi have stated they will market

the JVC VHD-system videodiscplayers, probably in the first quarterof 1982.

There is no compatibility betweenthese three types. A disc intendedfor one type cannot be placed onanother's turntable. If forced tooperate in a mismatched machine, adisc would not produce either soundor picture.

Although this incompatibility isdetrimental to efficient sales andservicing processes, it is a technicaldisagreement that apparently mustbe solved by the buying public. Novalid prediction can be made aboutwhich system will emerge victorious.Therefore, technicians should learnto diagnose and repair all videodiscplayers.

It is not practical to cover all ofthe small details of videodisc -playercircuitry in a magazine, because ofthe huge volume of material. For ex-ample, the RCA SFT-I00 PlayerTechnical Manual contains 84


COMPARISON OF VIDEODISC SYSTEMS

MAJOR SUPPLIERS

FEATURES

DISC TYPE

MAX PLAYING TIMEPER SIDE

VIDEO CARRIER

CHANNEL 1 AUDIO

CHANNEL 2 AUDIO

LUMINANCEBANDWIDTH

AUDIO RESPONSE

CHROMA FREQUENCY

DISC ROTATION

PICKUP TRAVELACROSS DISC

CED LASERDISC VHD

RCA, ZENITH, ETC.

F/R RAPID ACCESS,PAUSE,F/R VISUAL SEARCH

GROOVED,CAPACITANCEREADING

1 HOUR

5MHz

716kHz

NOT AVAILABLE

3MHz

20Hz-20kHz

BURIED 1.53MHzSUBCARRIER

450rpm

OUTSIDE TOINSIDE

MAGNAVOX, US JVC, GE, ETC.PIONEER, ETC.

SAME AS CED, PLUS:F/R SLOW MOTION;STILL; 7/R STEP;FRAME SEARCH(PIONEER ONLY)

GROOVELESS,LASER -OPTICAL

1 HOUR

8.1MHz

2.3MHz

2.8MHz

3.5MHz

40Hz-20kHz

STANDARD 3.58MHzSUBCARRIER

1800rpm FOR CAV.600 to 1800rpmFOR CLV

INSIDE TO OUTSIDE

SAME AS LASERDISC,PLUS 10 -SEGMENTPROGRAMMABILITY

GROOVELESS,CAPACITANCEREADING

1 HOUR

6.6MHz

NOT AVAILABLE

NOT AVAILABLE

3.1MHz

20Hz-20kliz

NOT AVAILABLE

900rpm

NOT AVAILABLE

Table 1 This listing showsthe comparativespecifications andoperating featuras of thethree types of videodiscsand videodisc players.

pages, plus large schematics. Evenso, the RCA coverage seldom ex-tends beyond the block -diagram andsimplified -explanation format.Therefore, only the basics andgeneralities are covered in this arti-cle.

ComparisonsSpecifications in Table 1 show the

major technical differences betweenthe three types of videodisc players.Magnavox and Pioneer discs haveno grooves, but the audio and videosignals are stored in an FM variationof pits placed in a groove -like spiral,starting at the disc's inside and end-ing on the outside. Variations inpit spacings are read by a laser beamand decoded into individual audioand video signals. Thus this is agrooveless, laser -optical, light -reading videodisc system.

The RCA CED videodisc is agrooved, capacitance -variation -reading type with a continuousspiral groove (outside to insidestylus movement), having verticaldepth variations spaced according

to the FM signal. A diamond styluswith a tiny deposited -metalcapacitance plate follows the grove;

a mechanism assists the movementof the large stylus -pickup assembly.

Fewer details are known of the

Servicing of a Pioneer VP1000 begins by removal of the bottom, and placingthe unit in a 90° vertical test rack. All circuit boards are shown in operatingpositions.


Servicing videodisc

JVC and GE VHD system. TheVHD discs have no continuousgrooves, but the signals are encodedin the FM placement of pits arrang-ed in a spiral -groove pattern. FMcapacitance variations along thegroove pattern of pits are sensed bya metal plate on the stylus. Thestylus rides on the disc surface, butis moved by a servo system so thatthe metal pickup plate is exactlyover the spiral of pits. The VHD canbe called a grooveless capacitance -reading system.

One similarity between the threesystems is that they supply audioand video signals from decoding anFM carrier previously recorded onflat, round discs strongly resemblingconventional audio phonographrecords.

The systems cannot record pro-grams, although it is rumored thatPioneer is investigating a method ofadding recording.

Features common to all threetypes include: forward and reverserapid access, forward and reversefast play, and pause. Because of themore sophisticated servo drive andthe arrangement of video fields onthe disc, the grooveless models can

Figure 1 Slider assembly of a Pioneer model VP -1000 is shown here. At the top isthe HeNe laser tube.

also provide stop -motion andframe -search functions. The frame -search feature allows the viewer toselect continous playback of any ofthe approximately 54,000 frames onone side of the disc.

Only the laserdisc and VHDsystems have stereo sound, althoughRCA may introduce this in newermodels.

All three systems have micro-processor controls of functions,plus readouts or displays of thevideo -frame number or the elapsedtime. Picture and sound qualities

While the Pioneer VP -1000 is in the vertical test rack, two circuit boards can berotated, exposing other wiring below the mechanism.

are much better than those broad-cast by TV stations.

Optical laserdiscSignal information of a laser -type

videodisc is recorded on a single"track" that makes thousands ofwidening spirals as it circles fromthe disc's center to the end at theoutside edge. This appears to besimilar to the old commercial"inside -outside" phonographrecords. These tracks, however, arenot amplitude -variation audiogrooves, but rather a series of pits orindentations in the base material.

After the properly located pits arepressed into the transport plasticbase of a half disc, a thin layer ofreflective aluminum is placed (byevaporation in a vacuum) on thesurface, followed by a protectivecoating. Finally, two sides are sand-wiched together to form a single2 -sided videodisc.

During play, the laser beam thatis used to track the line of pits(Figure 1) is simultaneously intensi-ty -modulated by the pits. Brighterlight is reflected from the surfacebetween the pits than from the pits,and this varying level follows theFM carrier recorded on the disc.

Nothing but the laser light beamtouches the disc during playback, sothere is no wear or other alterationof the disc. Also, slight scratches orsmudges on the surface do not in-terfere with retrieval of the FMsignal, so extreme care during dischandling is not required. Of course,


Servicing videodisc

FIRST -ORDER

ITRACKINGI

BEAM

PITS

ZERO -

ORDER

BEAM

ZERO -ORDER BEAM

C )ADJACENT

TRACK

DESRED

TRACK

ADJACENT

TRACK

FIRST -ORDER

'TRACKING) BEAM

Figure 3 The center "track" of any three adjacent pit "tracks" is scanned by thezero -order beam, the one that handles the video/audio signal. The two first -orderbeams scan the adjacent "tracks" at right and left of the signal track. Thesefirst -order beams are used to correct any radial misplacement of the zero -orderbeam. Proper operation produces equal signals from the E and F photocells thatmonitor the light reflected from the adjacent "tracks."

gross damage can degrade the pic-ture.

FM signals-Signal informationencoded on the laserdisc is the resultof these three FM signals: 8.1MHz carrier that is frequency -

modulated by composite video(including normal NTSCchroma);

2.3MHz carrier, frequency -mod-ulated by the channel -1 sound;and

2.8MHz carrier, frequency -mod-ulated by the channel -2 sound.

In contrast, most videocassetterecorders (VCR) separate anddown -convert the chroma to a lowfrequency during recording, fol-lowed by up -conversion and recom-bining with the luminance signalduring playback. This process candegrade the signal quality; apossibility that is eliminated in thelaserdisc by handling the chromawithout separating it from theluminance.

Frequency modulation of thesound channels provides better fre-quency response and a higher signal-to-noise ratio than is obtained fromVCR's using direct recording on thetape.

DiscsTwo types of discs are available

for playback on optical machines.The standard -play type (also calledCAV, for Constant Angular Veloci-ty) requires a constant disc rotationof 1800 rpm with each revolutionof the disc carrying one frame ofvideo. Sync pulses are alignedsimilar to spokes of a wheel withthese CAV discs. This makes possi-ble special effects such as frame -by -frame advance, slow -speedplayback and random search, whichare not possible with CLV discs.CAV discs play for 30 minutes perside.

Extended-play (or CLV, for Con-stant Linear Velocity) discs play onehour per side, double that of theCAV types, but the rotation variesfrom 1800 rpm at the inside start to600 rpm at the edge of the disc.The varying rotation prevents use ofsome special effects, as describedbefore.

The laser beamFigure 2 shows a simplified draw-

ing of the beam paths when playinglaserdiscs. The helium -neon gaslaser emits a beam of red light hav-ing a wavelength of 632.8nM. First,the beam passes through two

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r

RADIAL (TRACKING

MIRROR

I/4 WAVE

PLATE

PHOTO

DETECTOR

LASER DISC

1.1

LASER TUBE

TANGENTIAL

MIRROR

OPTICAL

DIVIDER PRISM

413 CYLINDRICAL

LENS

DIVERGING

LENS

0GRATING

FIXED

MIRROR

FIXED

MIRROR

LASERDISC SLIDER ASSEMBLY

Figure 2 These components on the laser slider unit focus and move the laser beams as required for proper reading of thedisc "tracks" of pits.

Servicing videodiscdirection -changing mirrors thatbring the optical axis to the standardposition on the slider. Next, thebeam passes through a grating thatsplits it into a number of beams.Only the center (zero -order) beamand the two first -order beams adja-cent to it are used, although moreare formed. From the grating, thebeams pass through a number of op-tical components, from the trackingand tangential mirrors, through theobjective lens and onto the disc.

From the disc surface, the beamsare reflected in varying degrees ofbrightness, depending on therecorded information. Coming backalong the beam's previous path, thereturning beams are diverted by theoptical divider prism and cylindricallens, finally reaching the photo -detectors. These photo -detectorschange light -variation levels intovarying electrical signals that are

used to control the servo system,and also to provide the video signalafter demodulation.

Beam -guide servosThe motor -driven platform

holding the optical components iscalled the slider assembly. Its pur-pose is to track the line of pits, thusproviding faithful reproduction ofpicture and sound. The sliderassembly has about the same func-tion as the tonearm of a recordplayer.

The servo systems that move theslider system are described separate-ly.

Focus servoThe purpose of the focus servo is

to minimize divergence of the laserbeam on the disc's surface.Manufacturing tolerance of thediscs allows some deviation from

1

perfect flatness, and this varies thedistance between the objective lensand the disc surface.

The focus signal is generated bysampling a portion of the laser beamthat is reflected from the disc andpassing it through a special cylin-drical lens. The beam from thelens is focused on a 4 -quadrantphotodetector (Figure 3). When allfour quadrants are equally il-luminated, the beam is in properfocus. Any imbalance of illumina-tion indicates focus error, and a cor-rective signal (Figure 4) is generatedto operate a coil (surrounding theobjective lens) and move it up anddown to improve the focus.

Radial tracking servoControl of radial tracking

(sideward movement of beam) isaccomplished by two servo me -


chanisms: tracking and slider. Thepurpose of the tracking servo is tomaintain accurate centering of thebeam on the appropriate track. Thefirst -order beams are used to readthe tracks adjacent to the one withthe desired video/sound signal. Aseparate photodetector is used foreach beam (E and F photocells inFigure 4). When both photocellsreceive equal light levels from thetwo adjacent tracks, the radial -errorsignal is zero, and the zero -ordersignal beam must be correctlycentered.

If the zero -order beam drifts toeither side, the E and F first -orderbeams are not balanced, and theradial -error signal drives the track-ing mirror electromagnetically in thedirection that corrects the im-balance.

The accuracy of this system de-pends on equal spacing betweentracks of pits in the disc, which re-quires precision in the recording andmanufacturing processes.

Slider servoMaximum correction by the

tracking servo is limited by the rota-tional angle of the tracking mirror.Therefore, it is necessary to provideanother control mechanism that in-creases the tracking -mirror range.This is accomplished by the sliderservo.

Dc voltages of the tracking -errorsignal are extracted and used to con-trol a motor that moves the sliderassembly. For example, the trackingmirror is tilted to move the beamsnearer the outside edge of the disc asit is played. Finally, the mirrorreaches the limit of its range. Fur-ther moving of the track of pitstoward the disc edge generates an er-ror voltage that activates the slide -drive motor, which then moves theslide assembly outward, thus allow-ing the tracking mirror to again per-form delicate adjustments from aposition nearer the center of itsrange.

Therefore, the slider and trackingservos operate as a team to controlthe radial movements of opticalcomponents that recover the desiredsignals from the videodisc.

Speed controlProper reproduction of color and

luminance in the TV pictures

ABCD

PHOTODIODES

SUM

A B

CSUM

I

OFF

AMP

1

PHOTODIODEPREAMP

OFF NF

BOOST

wiAt00 `,11AA!

FOCUS

ERROR

TRUE

RADIAL

ERROR SIGNAL

COMPENSATED

RADIAL ERROR

SIGNAL

Figure 4 In the photodiode preamplifier circuit, several summing and differencecircuits provide the total FM signal, a focus -error signal, the true radial -errorsignal, and the compensated radial -error signal that are sent to the properfollowing stages.

demands that the playback signal befree from liming errors. This is notpossible from any kind of direct un-controlled motor drive. Therefore,two servo systems accurately controlthe disc's rotational speed.

Gross speed control is the respon-sibility of the spindle servo. First,the circuit applies power to themotor when the sensors reveal that adisc is on the turntable and the lid isclosed, bringing the motor up to ap-proximate operating speed by refer-ring the actual speed against a presetreference. Action of this spindle ser-vo is sufficient to eliminate time er-rors at frequencies below 30Hz. Toreduce errors above 30Hz, thetangential -mirror servo is used.

An accurate control of relativetrack -to -beam speed is imperative,because even small errors of rota-tional speed can produce tintchanges, loss of color, or other pic-ture degradations. It is not practicalto control the turntable speed withthe required degree of accuracy,because of turntable inertia.

An ingenious tangential -mirrorsystem provides the small degree ofrapid compensation needed to cor-rect the relative speed between discand laser beam. An error signal isproduced by the comparison of aninternal reference against a signal

derived from the chroma burst com-ing from the disc playback. The er-ror signal electromagnetically movesthe tangential mirror to vary thebeam landing ahead or behind onthe track of pits. This compensatesfor instantaneous speed variations.

Servo summaryThe focus servo provides the

radial -tracking mechanisms (sliderand tracking) with signals thatminimize beam divergence. Thisalso insures best pickup of the en-coded FM video and audio signals.

Turntable speed and time -base ac-curacy are determined by the spindleservo, which references the turn-table speed to an internal standard,and the tangential -mirror servo thatcompensates for small variations intrack speed by comparing playbackchrorna burst to an internalreference.

The previous explanations applyto Pioneer and Magnavoxmachines, although the terminologymay differ slightly. Although theoperation explanations were notgiven in detail, they are sufficientfor scme repairs. Technicians whoplan to do many videodisc repairs,however, should seek additionaltraining from the manufacturersand other sources.


Servicing videodisc

PHOTO

DIODES

PRE

AMP

SOUND

DEMODat

SOUND

DEMOD

*2

N.;

AMP

SPLITTER

LINE

DELAY

IH

DROP

OUT

DETECTOR

VIDEO

DEMOD-1

USER

SWITCH

AUDIO

This test bench is equipped forservicing Pioneer VP -1000 videodiscplayers, and it includes theseinstruments: scope; digitalmultimeter; video test disc; TVreceiver; and an audio amplifier withspeakers for stereo tests. A testrack and hand tools are also shown.

DECODER

PICTURE

NUMBER

VHF

OSC

MODULATOR

VIDEO

DEMO()aZ

VIDEO

AMP

VIDEO

ELECTRONIC

DROPOUT SWITCH

TO TV

ANTENNA

TERMINALS

LASERDISC SIGNALPROCESSING

Figure 5 Operation of the signal processing circuits in laserdisc machines isshown by this block diagram.


The optical test and adjustment bench at the Pioneer factory -service facility is shown. Slider assemblies are shipped herefrom independent service centers for repair and alignment.

Signal processing circuitsOutputs of the photodetectors

(Figure 4) are sent to a preamplifierthat also supplies negative bias tothe diodes.

Diodes A, B, C and D are il-luminated during normal operationby reflected light of the zero -orderbeam. Signals A + B and C + D aresummed and distributed. These aresummed again (producing A + B +C + D) to form the total FM signalcontaining video and audio infor-mations.

The A + B and C + D signals alsopass through a difference stage toproduce the (A + B) - (C + D) focus -error signal.

Outputs of photodiodes E and Fare subtracted to yield a radial -errorvoltage that controls the trackingand slider servos. The true radial -error voltage is used only duringscan or jump functions, while the

compensated radial -error signal(with increased high -frequencyresponse) operates the servo systemduring normal playback.

From the preamplifier, the totalFM sign& is sent to a combinedfilter and high -frequency amplifiercircuit (Figure 5), which divides thesound FM from the video FM. Thesound FM signal is supplied to twotuned frequency -sensitive detectors,producing the channel -1 andchannel -2 audio signals that, afterchannel selection by the viewer, areapplied to the VHF oscillator/modulator unit.

The separated 8.1MHz video -FMsignal is sent to a demodulator,which recovers the composite video.The video then is routed to a clip-per/decoder that extracts the frame -number information. This frame -number data and the demodulatedvideo are fed to an amplifier, whose

output signal goes to the VHF oscil-lator/modulator unit that suppliesthe TV -receiver antenna terminals.

Dropouts are instantaneous lossof the 8.1MHz carrier because ofminor irregularities or damage ofthe videodisc. Dropouts are cor-rected by delaying the video -FMsignal by the time of one horizontalline and recovering the video indemodulator #2 (Figure 5). Adropout -detector monitors the levelof the 8.1MHz carrier and outputs apulse when the carrier disappears.The detector output pulse activatesan electronic switch, which thensubstitutes the composite video forthe normal video from demodulator#2. In other words, dropout loss ofvideo is corrected by substitution ofa previous line of video that hasbeen delayed for the purpose.Usually, dropouts are not noticeablewhen properly corrected.


Semiconductorsource guide

The demand for semiconductor replacement parts has given riseto many catalogs of cross-referenced parts. A brief description ofsome of these sources follows. Books, catalogs and cross-reference pamphlets are included.

Some cross-reference materials are free, but most are availablefor a small fee. To receive additional information, circle the ap-propriate number on the readers service card.

CodiThe CODI brand of rectifier

bridges and discrete diodes aredescribed in a Product Summaryfolder with additional specificationsheets.

Diode types include zener,temperature compensation, variablecapacitance, ultra -low leakagediodes, and sharp -knee low -noisezener diodes. Silicon rectifiers andbridges are available in mostratings.


D.A.T.A. Inc.The D.A.T.A. electronics book

information series is an extensive in-dex to semiconductor devices andspecifications. It consists of a22 -title semiconductor/IC selectionsystem involved in the R/D, design,engineering and purchasing of hightechnology electronics components.

The book series includes Tran-sistors, Discontinued Transistors,Diodes, Discontinued Diodes, Thy-ristors, Discontinued Thyristors,Consumer ICs, Microprocessor ICs,Microcomputer Systems, Optoelec-tronics, Discontinued Optoelec-tronics, Microwave, DiscontinuedMicrowave, Type Locator, Discon-tinued Type Locator, Digital ICs,Linear ICs, Interface ICs, MemoryICs, Discontinued ICs, PowerSemiconductors and ApplicationNotes.

Each book contains a master in-dex of devices, manufacturers anddetailed technical sections thattabulate characteristics, connectionsand outline drawings.

These books can often be foundat distributors' and at manufac-turers' regional offices.


General ElectricGeneral Electric Replacement

Semiconductor Guide no. ETRM-4311T has 546 pages of technical in-formation about semiconductorsand an extensive cross-indexing sys-tem.

Products include silicon and ger-manium transistors, diodes, rec-tifiers, voltage regulators, MOV,focus resistor assemblies, transientprotectors, ICs, SCRs and triacs.


International RectifierThe International Rectifier Semi-

conductor Replacement CrossReference Guide is designed to pro-vide data on the complete line of IRproducts.

The IR replacement numbers in-dicate the nearest IR equivalent and,in most instances, provide the userwith an exact replacement device, orone of greater current and/or volt-age rating. The user must qualifythe replacement acceptability by

reviewing the electrical, mechanicaland thermal characteristics of the

INTERNATIONALRECTIFIER

SEMICONDUCTORREPLACEMENT

---- GUIDEIOR

specific devices involved.Circle (47) on Reply Card

CeTECHNICIAN

COMPONENTSGROUP

Replacement Master GuideSonwanductors Industnal Entenarcomw.

Cornmang and MR0 Apphratbons

New -Tone ElectronicsNew -Tone Electronics is offering

16 Electronic Servleina SAntamhar 1 QR1

its new TCG Replacement MasterGuide to MRO, service dealer andOEM purchasers of replacementdevices through the company'sdistributors.

The guide consists of more than450 pages of listings on 1700 TCGreplacement semiconductors, cross-referenced to over 170,000 replace-ment equivalents.

Each page provides specificationsand diagrams on TCG replacementdevices, as well as an extensivecross-reference matching them withreplacement equivalents. The guidecontains over 600 TCG devices notpreviously listed.


Philips ECG Inc.The ECG Semiconductor Master

Replacement Guide lists more than2500 Sylvania solid-state replace-ment devices used as substitutes fordomestic or foreign units in enter-tainment, commercial and industrialequipment.

The 432 -page book contains morethan 350 new types, including highnoise immunity logic families,microprocessor devices and randomaccess memories. Also included areadditions to existing lines of bipolarand RF transistors, industrial rec-tifiers, silicon -controlled rectifiers,high voltage devices, linear ICs andCMOS and TTL digital ICs.

The technical section also in-cludes data on transistors, diodes,rectifiers, thyristors, linear anddigital modules, and ICs.


The Transistor Transistor LogicData Manual contains data on morethan 250 TTL devices in the semi-

conductor replacement line. Eachinformation sheet contains all thepertinent dc and ac information forthat replacement part.

The Selector Guide section con-tains information about buffers/inverters, Schmitt Triggers, regis-ters, latches, arithmetic functions,memories, counters, multiplexers,decoders/demultiplexers, driversand transceivers/receivers.

The Product Information sectionincludes general ratings and circuitcharacteristics, design considera-tions, power supply decouplingdata, and a CMOS-74C series.


/SemiconductorReplacementGuideiN:LUDES OVER 100.000SEMICONDUCTOR SUBSTITUTIONS

4.4

tit

ffn.

Radio ShackSemiconductor Replacement Guidecatalog no. 276-4005 from RadioShack has 88 pages of specificationsabout Archer display devices, ICs,diodes, transistors, SCRs, triacs,optoelectronic devices and generalinformation. Also, there are about200 unnumbered pages that cross-index 100,000 semiconductor substi-tutions.


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1981 roundupcalendar

ElectronicServicing,OctoberSoldering and desolderingequipment

DecemberSignal generator roundup


Semiconductors

*1§6iesz* 1981 Replacement Guide

Consumer Industrial/MROOre, 170.000 Solid State Replacement Recommendations

RCAThe 1981 SK Top of the Line

Solid -State Replacement Guide listsmore than 1300 solid-state replace-ment devices that replace more than170,000 domestic and foreign types.

The 408 -page guide shows the SKstock number along with the stocknumber of the numbering systemused by ECG (GTE Sylvania), RENand TM, to help locate the correctsolid-state device. The guide offersinformation on the complete line ofRCA transistors, rectifiers, thyris-tors, ICs and high voltage triplers,including many MRO replacements.


gm(lberies

Maintenance

Repair

*OperationsJEDEC and CommercialReplacement Devices....r.... yeac ICA 11, 01.1ftale

The RCA MRO Solid -StateManual for JEDEC and Commer-cial Replacement devices is a new64 -page manual that offers abridged

data on 2800 JEDEC and commer-cial devices.

One feature of the manual is across-reference listing of 11,580 ad-ditional JEDEC and Commercialtypes. The manual also eontainsdata on 12 axial -lead rectifiers forindustrial use and 26 full -wavebridges from RCA's SK seriesreplacement line.


RSM SensitronA 12 -page specification booklet is

offered by RSM Sensitron. It coverspower rectifiers, bridge rectifiers,three-phase bridges and NPN siliconpower transistors.


Semlkron InternationalSemikron International offers a

38 -page Condensed 1980 Catalogfeaturing physical and electricalspecifications for diodes, rectifierbridges, high -voltage diodes, MOVtransient protectors, heat sinks andSCR thyristors.


Sylvania

ECGSemiconductors

=if/RifMaster Replacement Guide Entertainment Industrial Commercial Equipment Maintenance and Repair

'"= "NO OUN.

SylvaniaSylvania is offering their 11th edi-

tion ECG Semiconductors MasterReplacement Guide for the enter-tainment, industrial, commercialand MRO markets.

The guide features more than 350new products and more than 27,000new crosses. Included in the434 -page catalog is information on

transistors, high voltage devices,diodes and rectifiers, zener diodes,and more. Also included is a list ofaccessories and a replacement direc-tory. The catalog includes analphabetical and numerical productindex.


Sylvania's ECG SemiconductorsDigital Integrated Circuits DataManual contains product informa-tion for the more than 285 TTLdevices in the ECG semiconductorreplacement line. Each individualdata sheet is self-contained with all

Sylvania

ECGSemiconductors

Mat L-,

P. NO

Digital Integrated Circuits Data Manual

pertinent dc and ac information forthat device type.

The logic devices described in thismanual differ widely in funciton,complexity and performance, buttheir electrical input and outputcharacteristics are similar and aredefined and tested to guaranteecompatibility. The data sheets thatmake up this book cover the majorcategories of TTL circuits.


ThordarsonTech -Mate Complete Semicon-

ductor Cross -Reference Guide no.TSH-3 from Thordarson has tech-nical tips, product data and cross-reference information for tran-sistors, SCRs and SCSs, thyristors,diodes and rectifiers, zeners, voltagemultipliers and ICs. Universalreplacement semiconductors cover


DIORDA

COMPLETE

SEMICONDUCTORCROSS REFERENCE

GUIDE 7

service requirements for more than100.000 devices.


Small Signal Low Noise Transistor forHigh Performance Receiver Applications

i

" :Z.: E. 011.04

1T4700

icon, f ,v` Lam Mow Om* Mk frevuomvMaier

Vs.Vw. 400* V

Mee Ovnanyv

MM vonvolv

I

_

TRW SemiconductorsA 4 -page data sheet describes

TRW Semiconductors' LT4700small signal, low noise microwavetransistor that features a 6 GHzgain -bandwidth product (Ft) and aminimum noise figure (NFmin) of1.6 dB at 1 GHz.

The data sheet, Small Signal LowNoise Transistor for High Perfor-mance Receiver Applications, pro-vides the following charts: typicalnoise figure and associated powergain vs. frequency, noise measurevs. frequency, noise figure vs. col-lector current, gain -bandwidth pro-duct vs. collector current, insertiongain vs. collector current and outputpower vs. collector current. Also in-cluded in the data sheet is a tabula-

tion of "s" parameters vs. frequen-cies from 100 MHz to 2 GHz. In ad-dition, noise parameters aretabulated for 0.5, 1.0, 1.5 and 2.0GHz.


10 WORKMAN.1.1140Nii

CMOSFVNR

DIODES

DTL

HV7P

/, ,A:

Workman Electronic ProductsThe Semiconductor Catalog and

Cross Reference Guide fromWorkman offers more than 160,000listings. This guide, with more than250 pages, provides device descrip-tions, device usage data, symbolsand nomenclature background,competitive cross reference andspecifications.

Listings include PNP and NPNsilicon and germanium transistors,RF transistors, HV Triplers, switch-ing transistors, color TV ICs, zenerdiodes and silicon diodes. One newdevice is the Sil-Pad, which replacesmica insulators under power tran-sistors without requiring siliconeheat -transfer compound.


ZenithSpecifications of Zenith univer-

sal -replacement semiconductors, acompetitive cross-reference to GE,RCA and Sylvania, and a full cross-index for industry numbers are inthe Zenith Radio Corporation'sUniversal Semiconductors guide.

The guide lists a line of semicon-ductor devices which replaces morethan 158,000 devices now used inelectronic products. The guide is

ZenithUniversal

SemiconductorsA unique,

one numbering systemof exact and selected

semiconductorreplacements.

composed of a 1 -number system ofexact and selected semiconductorreplacement parts.

Use of the guide permits a servicetechnician to use Zenith semicon-ductors in a wide range of consumerelectronic products such as colorand black -and -white TV sets, stereosystems and radio, and personal andbusiness computers.


This month's semiconductorsource guide is a sampling of prod-uct catalogs based on informationsupplied by those companies toElectronic Servicing. Other com-panies that provide similar catalogsmay be written to directly.

To get moreinformation...on items advertised ordescribed in this publica-tion, use the Reader Ser-vice Card.As a free service for ourreaders, we forward yourInquiry to the product'smanufacturer. Reader Ser-vice Card is pre -ad-dressed.


Servicingshutdown circuits

By Homer L. Davidson

Several years ago, in response topressure for safer TV receivers, TVmanufacturers devised severalmethods of disabling any colorreceiver that developed excessivehigh voltage, which can producesoft X-rays in the picture tube.

These safety circuits usuallyoperate using one of these two basicactions: The overvoltage condition acti-

vates the protective circuit, whichproduces an out -of -lock picturethat is either vertical or hori-zontal, but usually horizontal.The erratic slanted or rollingpicture discourages the viewerfrom further operation of the re-ceiver. Also, the erroneous hori-zontal -sweep frequency is in thedirection that reduces the highvoltage. This type of safety oper-ation is called hold-down be-cause it reduces but does noteliminate the high voltage andpicture brightness.

T602

FLYBACK

II

POS GOING PULSES24 V PP

47

Troubleshooting color receiverscontaining shutdown orhold-down protective circuits canbe very tricky, because falseoperation of the protectivecircuits can simulate defects inhorizontal -sweep or high -voltagesections.

Most newer color receivers in-corporate a safety circuit thatkills the horizontal sweep whenany high -voltage overvoltage oc-curs, thus eliminating the picturealong with the excessive voltage.This type is called shut -downbecause it eliminates the hori-zontal sweep, high voltage andpicture.From the servicing standpoint,

these safety functions mimic othermalfunctions. A color receivershowing a horizontally out -of -lockpicture might have a genuine defectthat has changed the horizontal -oscillator frequency. Or it couldhave excessive high voltage that hastriggered a hold-down protectivecircuit. Even worse, the hold-downcircuit might have a defect.

Similarly, a genuine horizonta-sweep defect might have killed thehigh voltage and picture. Or ex-cessive high voltage could have ac-tivated a shutdown safety circuitthat eliminated the sweep.

Therefore, the first step in analyz-ing a symptom that could originatein the shutdown or hold-down cir-

SHARP

cuit is proving whether that circuithas been activated. Second, testsmust be made to determine if ex-cessive high voltage or shutdown/hold-down defect is responsible.

No efficient troubleshooting orrepairs can be made before the con-dition is known about anyshutdown/hold-down circuits. Thissometimes becomes difficultbecause of the many circuits used invarious models, and the lack of in-formation about disconnecting theprotective circuit.

A simple hold-down circuitThe Sharp color TV portable

model I3D38 (Photofact 1934-2)has an uncomplicated hold-downcircuit (Figure 1). Unless the highvoltage rises above the design level,the circuit does nothing.

Pins 2 (ground) and 10 of flybackT602 supplies heater power for thepicture tube. Horizontal pulses forthe hold-down circuit are also takenfrom pin 10 through R653 and R655to diode D651, which rectifies thesweep signal producing about+ 16V. C652 is the filter capacitor

TO 1501

C651

10 itF

PIN 3

Figure 1 A zener (ZD651) blacks dc voltage produced by rectification of flyback pulses until the voltage is larger than the zenerrating. Then ZD651 passes positive voltage to IC501 pin 3 to change the horizonta+ frequency.

A technician is shown testing voltages with a digital meter in the horizontal stages of a color receiver that includes a shutdowncircuit. Also needed are a good scope and high voltage meter.

that makes the rectification peakreading, while R654 is the normalload.

A second load is the series con-nect:on of zener ZD651, R652 and8651. The zener has a rating of 20V,however, which means it will notpass any appreciable current orvoltage until the zener voltage is ex-ceeded. Any condition in the hori-zontal -sweep circuit that producesexcessive high voltage also increasesthe nominal + 16V (at ZD651cathode) above the 20V rating. Thisplaces a positive voltage at pin 3 ofIC501, and the IC changes thehorizontal frequency enough thatthe horizontal -hold control cannotrestore proper locking.

Integrated circuit IC501 is multi-purpose, providing sync separation,

horizontal oscillation, B + regu-lation, vertical oscillation, AFCdetection, and safety control of thehorizontal -oscillation frequency.

Testing the SharpDisconnecting the hold-down cir-

cuit in this Sharp is easy. Eitherdisconnect one lead of D651, orshort across R651 (IC501 pin 3 toground). if the horizontal frequencychanges and then can be locked nor-mally to a station, then the hold-down circuitry was causing theprevious out -of -lock condition. Thistest is based on the fact that thehold-down circuit does nothingunless the high voltage is excessive.Therefore, disconnecting the hold-down stage should not interfere withnormal horizontal locking.

A second step is vital when thetest shows normal locking with theprotection stage disconnected, butnot with it connected. The highvoltage must be measured im-mediately and reduced to normal ifit is excessive. The receiver shouldnever be operated for more than aminute or two with the safety circuitdisabled, because if the high voltageis too high it can damage other com-ponents or the picture tube.

In cases in which the high voltageis normal but the safety circuit has adefect, do not merely disconnect it.Instead, repair and reconnect it.

Measure the dc voltages in theFigure 1 safety circuit and then testall resistors and diodes. Zener diodeZD651 can be disconnected andtested for forward conduction and


Shutdown circuits

reverse leakage. If both tests havenormal results, the zener is probablynot defective.

If disabling the safety circuit doesnot correct the out -of -lock horizon-tal, IC501 should be replaced.

RCA shutdown circuitA 2 -stage overvoltage protector

circuit is included in RCA and J. C.Penney CTC101 chassis (Figure 2).When this circuit is activated,perhaps from excessive highvoltage, it kills all gain of thehorizontal -drive transistor. Howthis momentary elimination of drivetriggers shutdown of the entirereceiver is an interesting story.

All low -voltage power supplies inthe CTC101 (except the line -rectified raw power at the regulatorSCR) are produced by rectificationof horizontal -sweep pulses. A start-up circuit provides a pulse of

RCA CTC99

HORIIPULSES

RED WIRE

xD

R421 .e

2200

XI TEST

POINTS

XII

R428

C425.1

1430

10K

10

R429

21.641:

R43I

47.5K

1432f164 !00

+ 16V

54VRP

positive dc voltage to start theoscillator and driver each time theline power is switched on. Any inter-ruption, even for less than a second,triggers shutdown that eliminates alldc voltages except the line -rectifiedsupply. Without horizontal sweepand high voltage, there can be nopicture or sound.

Safety circuit operationSuccessful servicing of the safety

shutdown circuit requires aknowledge of normal circuit opera-tions.

Positive -going pulses from the redwire of the flyback are rectified bydiode CR424, producing abou:+ 41Vdc at testpoint XT (CR424cathode). The dc voltage falls orrises in step with amplitude of theflyback pulses. This is also true ofthe high voltage, so they vary in thesame percentage. The shutdown cir-

I C424CR424 ""sm

.41./

20.3V

1434

FROM BEAM330K

LIMITER

PNP

Q404 X RAY

COMPARATOR

cuit operates only from dc voltages.A sample of the +41V varying

voltage is fed to the Q404 emitter,while the Q404 base has a regulateddc voltage derived from the +33Vsupply that is stabilized by zenerCR427. Thus the Q404 forward biaschanges according to the + 41Vvariations.

Notice that Q404 is a PNP polari-ty, so an increase of emitter positivevoltage (from the + 41V) is in-creased forward bias. In normaloperation when shutdown is notcalled for, the B/E is reverse biased,so Q404 is cut off.

The Q404 collector is directcoupled to the Q403 base, while theQ403 emitter is connected throughswitching diode CR419 to the baseof Q407 horizontal -driver tran-sistor. In normal operation, theQ403 emitter measures about -5V,produced by CR419 rectification of

1.1V DARK

UIV BRIGHT 29.34

C445

.22pI

FCR425

R423On

H4E-NAINe- ,'8.8V

1L- CR423

R433

iOn

294

15064.7M

TO HEIGHT

CONTROL CIRCUIT

C426

.47

143530.1K

X RAY LATCH

Q403

54

C423.47pf

33.34

5.44 PP

R424

!UOK-5.24

1E CR419

CTC99 OVERVOLTAGE SHUTDOWN

04271I 00pF T

R436824

fir--NAese-f 4 208V

1(pa \ CR427411 ) 33V

10 BASE OfQ407 HOW DRIVER


the Q407 base squarewaves.. AnR424, 100K resistor returns theQ403 base to its emitter, and the on-ly other base connection is to theQ404 collector. Because Q404 isnonconductive, Q403 has aboutzero bias, so it too is cut off anddoes not interfere with the Q407drive signal.

If the + 41V supply increases,Q404 has sufficient forward bias toconduct some of the emitter positivevoltage to the collector, making itpositive. This collector is connectedto the Q403 base, so Q403 also hasforward bias. Q403 conducts part ofits collector positive voltage to theemitter, where it passes throughdiode CR419 and applies a satura-tion overbias to the Q407 base. TheQ407 saturation positive biaseliminates most Q407 gain.Therefore, the drive drops below thelevel needed to sustain horizontal

sweep, and the entire sweep circuit isinstantly turned off.

Without a start-up voltage (notpresent except at switch -on), thereceiver remains dead. No latchingaction is required in the shutdowncircuit, because the horizontal can-not be restarted until the televisionis turned off and most of the voltagehas drained from the main raw -B +filter capacitor. When the receiver isswitched on after that waitingperiod, start-up will occur. If theshutdown circuit defect or the ex-cessive high voltage has not beencorrected, another shutdown willoccur instantly. But if all is well, thereceiver will operate normally.

TroubleshootingDuring shutdown, there are no dc

voltages in the receiver except in the+ 155V supply, which because ofthe light load will measure about

Figure 2 RCA CTC99 and CTC101 chassis have withtwo transistors that monitor dc voltage rectified from horizontal sweep.When the dc voltage rises abnormally, both transistors conduct. 0403conducts positive voltage to its emitter, then the voltage passes throughswitching diode CR419 to kill the gain of the Q407 horizontal driver.This shuts down all but the + 155V raw line -rectified supply.

Figure 3 The arrow indicates testpoints XT and XT1 in RCA CTC99 and CTC101chassis. As a test, these points are connected together to product shutdown. Itshutdown does not occur, the shutdown circuit is defective and must be replaced.

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The Advertising Council1981 United Negro College Fund, Inc.


Shutdown circuits

+ 165V. This can be a symptomeither of failure to start or normalstart-up followed by shutdown.

The easy way to test for a shut-down circuit that is defective andthus causing its own shutdownoperation is to disconnect either endof diode CR419. Warning: If thereceiver then operates while theshutdown circuit is defeated, thehigh voltage might be dangerouslyhigh. Test it immediately when apicture is obtained, then instantlyturn the television off if it is ex-cessive. But normal high voltage in-dicates a defective shutdown circuit,which must be repaired before it isreconnected.

First tests in the shutdown circuitshould include leakage checks ofboth transistors. Next, the presenceof +33V at the cathode of zenerdiode CR427 must be verified. Testswitching diode CR419 for leakage,also.

After the shutdown circuit hasbeen repaired or found to be nor-mal, it should be checked for properoperation. Short testpoint XT totestpoint XT1 (Figure 3) while thereceiver is operating correctly. Shut-down should occur instantly.Remove the short and wait withpower off for two or three minutesto allow the filter to dischargebefore switching on the ac power.Normal operation then should beobtained.

The RCA shutdown protectioncircuit has not caused any largenumber of servicing problems, but itis covered in detail here because ofthe potential for much wasted timeif a technician tests circuits that arenot defective.

A Japanese hold-down circuitIn Samsung model CT -332D por-

table color receivers, the hold-downtrigger is activated by the preciseboost voltage (Figure 4).

Resistors R709, R711, R712 andR713 form the top leg of a voltagedivider, while R704 is the bottomleg. The voltage divider reduces the+ 850V boost voltage to less thanIV at the Q702 base and Q701 col-lector. The Q702 emitter positivevoltage is stabilized by zener D701with load current from R705. Innormal operation, Q702 is noncon-

ductive because of insufficient bias.If the boost voltage rises, the

Q702 base voltage rises in step.Thus, excessive sweep and highvoltage conditions cause enough in -Crease of Q702 forward bias to pro-duce a small C/E current, whichreduces the Q702 collector voltage.

Notice that the Q702 collectcr isconnected to the Q701 base, so thereduced dc voltage there produces asmall C/E current in Q701, becauseQ701 is a PNP type. The Q701 C/Ecurrent brings positive voltage fromthe emitter to the collector, makingit measure more positive.

That is not the end of the action,for the Q701 collector is direct con-nected to the Q702 base. Therefore,Q702 has increased forward bias,which in turn increases the negativeforward bias of Q701 and thusraises the C/E current, which inturn increases the Q702 C/E. Thisaction continues with each tran-sistor's current increasing until bothtransistors are saturated (C/Eresistance is almost zero ohms).

The two transistors form an elec-tronic switch with action similar tothat in an SCR. Once the circuit istriggered and both transistorsbecome saturated, the conditions re-main fixed until power is removed.This resets the circuit; it is readywhen needed in another overvoltagesituation.

When the Q701/Q702 electronicswitch is activated, the circuit iscompleted through R506/R527,R701, Q701 E/C and R704 toground. This reduces the positivevoltage at the base of the Q501horizontal oscillator and increasesthe horizontal frequency. The effectis identical to a similar resistanceconnected in parallel with R508 andthe horizontal -hold control. Thereceiver is out -of -lock and cannot belocked with the hold control, whichdiscourages the viewer fromoperating the machine before it isrepaired. Additionally, the highersweep frequency somewhat reducesthe high voltage.

Operation of the hold-down cir-cuit can be tested when there is noovervoltage by shorting together ter-minals Dll and D12 on the sweepboard. The picture should becomeout -of -lock diagonal lines. Remove

the test short, switch off the TVpower and wait a few seconds, turnon the TV power and expect a nor-mal picture. If the receiver does notrespond as described, the hold-down circuit is probably defective.

To disconnect the hold-down cir-cuit for a short test, disconnecteither end of resistor R701. If thereceiver cannot be locked until thehold-down is disabled, but it worksafterward, the hold-down circuitneeds repair.

Normal troubleshooting pro-cedures should be adequate to findany defective components in thishold-down circuit.

SCR shutdownAn SCR is employed in the Mont-

gomery Ward model GGY-16217Bcolor receiver to kill the horizontalsweep when shutdown is neededbecause of excessive high voltage(see Photofact 1838-1).

Horizontal pulses from the T400flyback are clamped by zener diodesSC434 and SC433, with theunclamped part of the pulses rec-tified by diode SC435 (Figure 5).With normal high voltage, the pulseamplitude does not exceed theclamping level, so little positivevoltage is produced by SC435. R436is the load, and C432 is the peak -reading filter capacitor for theSC435 rectified voltage that is ap-plied to the gate of SCR430.

The anode and cathode ofSCR430 are connected between theB + load resistors (R430 and R438)and a point that is almost ground(R998 and R999). Therefore, whenthe SCR430 gate becomes sufficient-ly positive (about + 1V) than itscathode, the SCR conducts andremoves the B + supply voltagefrom IC400 pin 15. This eliminatesthe squarewave drive to the Q400driver transistor base and kills thehorizontal sweep.

The SCR430 cathode has a smallnegative voltage from the automaticbrightness -limiter (ABL) circuit. In-creased current through the picturetube increases the negative voltage.Therefore, excessive CRT currentand excessive high voltage (or eitherseparately) can trigger the SCR andkill the horizontal sweep and highvoltage.


HORIZ

HOLD 1508 1507 0503

BOOST

+850 V

Q701

R704

1800

R701

AAA.5600

27K 47K

1506

22KR527

C506

1702 1708

0705

4.7 tlf

R713 R7I2 R711 1709

680K 680K 470K 330K

3.31tF

22K

181' 10K

1705 1500

R710Anrs,470K

FROM

Is- FLYBACKPIN 6

Q501

HORIZ

OSC

4- 115V

SAMSUNG HOLD-DOWN

Figure 4 A Samsung hold-down circuit latches to produce an out -of -lock picture.

IFogure 5 Excessive high voltage or CRT current in a Montgomery Ward TV triggers SCR430, which killsthe drive to 0400 horizontal -driver transistor, shutting down the horizontal sweep and high voltage

1 V PP HORIZSQUAREWAVES FROM

IC400

PIN 15

+ V

ABL

R430

C438

112F

R438 1200

1200

SC996

C431

7-001I

+10VA

SCR430

+113 V --0`

R9988999

0.56

R433AA&

25 V PP

T400 BROWN /POSITIVEFLYBACK /

PULSES

TO CRT

HEATER

L434

+0.02 V

C432 Lr, 100 &F

-0.4 V

22

SC433

L432

FROM41-T400 PIN 3

8200

SC434

0434 .21 V

123 V

-6V

MONTGOMERY WARDSHUTDOWN

SC435

Q400

HORIZ

DRIVER

R436

2200

Figure 6 SCR430 of Figure 5sciernatic plugs into asocket (see arrow) so it canbe easily removed for tests.

Figure 7 The pin tip pointsto diode SC433 and R433of the Montgomery Wardreceiver in Figure 3. They arecove,-ed by insulatingspaghetti.

Figure 8 Many new flybackshave several high -voltagerectifiers encapsulated withthe KV windings. Makecertain the flyback is badbefore replacing it; thesnutdown circuit might bemimicing the symptoms ofa detective flyback.

If

,cai- nti 0

ey it'esit'sr 1

cif_7c SW 64

Shutdown circuits

After the shutdown circuit is trig-gered, it remains in that conditionbecause the SCR430 A/C currentdoes not drop to zero. It can be resetby turning off the ac power andwaiting a minute or two before reap-plying the power. If the cause of theprevious shutdown has beenrepaired or is not active at the mo-ment, the receiver should operatewith normal sweep.

Check for shut -down conditionby measuring the dc voltage at thejunction of resistors R430 andR438. If the voltage is near zero, theSCR is conducting, probably fromshutdown.

It is easy to prove whether theSCR is conducting. SCR430 isplugged into a socket (photographin Figure 6), and it can be unpluggedwhile the performance is observed.The SCR, strongly resembling asmall transistor, can be tested whileit is unplugged. If the receiver is inshutdown with the SCR but has apicture with it unplugged, the SCRwas conducting.

When the SCR is provednondefective, the next step is tomeasure the gate -to -ground voltage.If this is excessively positive, workback through rectifier SC435 andthe two clamp zeners to find thesource of the voltage.

Zeners SC434 and SC433 havebeen known to break down undercircuit load, but test normal out ofthe circuit. SC434 is rated at 21V,and SC433 is rated at 123V. Replaceboth if their condition is in doubt.SC433 is difficult to locate, becauseit and R433 are inside insulatingspaghetti on the bottom of the cir-cuit board (Figure 7).

Servicing shutdown/hold-down circuits

Successful troubleshooting of col-or receivers that have protectiveshutdown or hold-down circuits re-quires extra awareness that thosesafety circuits are in the receiver.The technician must also know whatthe protective circuit is supposed toaccomplish after it is triggered, andalso what conditions trigger the ac-tion. Several basic circuits have beenanalyzed here to provide the fun-damental principles.

For example, the first thought

many technicians have when con-fronted with a color receiver thathas no high voltage or horizontalsweep, is that the problem is in thehorizontal/high-voltage section,and probably involves thehorizontal -output transistor, theflyback, or the HV tripler. Thiscould be disasterous to the produc-tion schedule, if the receiver has ex-cessive high voltage or a defectivesafety shutdown circuit.

Circuits that shut down thehorizontal sweep usually do so byremoving the drive waveform at thebase of the driver transistor or theoutput pin of an IC that providesthe same function. Therefore, thefirst test should be for a properwaveshape and amplitude at the col-lector of the driver transistor. Ifthese are not dangerously belowratings, it indicates the problem islocated fart:ler downstream, andnot in the shutdown circuit.

When the driver base and collec-tor waveforms are found to besubstantially reduced, the shutdowncircuit must be suspected. Thefastest test is to disconnect the safe-ty shutdown where it connects to theactive circuit, such as the driverbase. If proper operation is ob-tained, there are two remainingquestions: (1) Is the high voltage ex-cessive, and triggering the shut-down, or (2) does the safety circuithave a defect that triggers itself?

The next step, therefore, is tomonitor the high voltage. If it is toohigh, make repairs before the safetyshutdown is reconnected. If the highvoltage is normal, the shutdown cir-cuit must be repaired.

Procedures for hold-down cir-cuits that force the oscillator out ofhorizontal lock are similar, but thesafety circuit should be discon-nected to determine whether thereceiver then can be properlylocked. If it cannot, the basic prob-lem is in the horizontal oscillator,and not in the hold-down stage.

Causes of excessive HVFew defects can increase the high

voltage by a significant amount.Some receivers regulate sweep andhigh voltage by regulating the dc -voltage supply that is applied to theoutput -transistor collector. Often

the regulating element is a powertransistor that can become shortedbetween collector and emitter. Thehigher B+ supply produces an in-creased high voltage. This is alsotrue for those models that use anSCR to regulate a B + supply.

Most models using a TO -3 type ofoutput transistor have one or morecapacitcrs connected approximatelyfrom collector to emitter, or acrossthe damper diode. These capacitorstune the yoke/flyback inductancesduring retrace (pulse time). There-fore, any significant reduction ofthis total capacitance increases thehigh voltage, almost in direct ratio.One of these capacitors usually islarger than the others, perhaps be-tweep 0 01µF and 0.02µF, and if itopens, the high voltage might climbto around 50kV - extremely danger-ous to technicians and components.These capacitors should be the firstcomponents suspected and tested.Remember, these must be typesdesigned for high -current pulse cir-cuits and having a high voltagerating.

An excellent technique with manynewer all -solid-state models is tomake preliminary tests while the linevoltage has been lowered by avariable -voltage transformer. Mostof these receivers will operate with asmall and dimmer picture down toabout 70Vac of line power. This is agood starting voltage for tests ofreceivers that persist in ruining out-put transistors or other expensivecomponents during power -on tests.

With receivers that trigger intoshutdown or hold-down conditions,it often is informative to begin theline voltage (measure the voltage)and notice which minimum acvoltage produces shutdown or hold-down action. During subsequenttests, the receiver can be operated atslightly below the triggering acvoltage.

Don't replace flyback (high -voltage) transformers withoutstrong proof that they are defective.Many present-day models includeseveral HV diodes inside the flybackassembly (Figure 8). Any service -type ohmmeter will indicate suchdiode/winding combinations asopen, whether the diodes or thewinding is actually open or not. 0

SQptember 1981 Electronic Servicing '7

The M10 module (below) isthe largest Zenith System -3module. It also is the onlyone mounted horizontally.M10 contains both line -operated power supplies,all scan -rectified powersupplies, the pulse -widthmodulator, two horizontaldrivers, one largehorizontal -output transistorwith heat sink, regulatorand high -voltagetransformers, theshutdown safety circuit,and pincushion -correctioncomponents.

By Carl Babcoke, CET

zenith power andhorizontal sweep

part 1The Zenith horizontal sweep and allscan -rectified power supplies on theM10 module are regulated by aunique circuit. No powertransformer is needed, but allvoltage supplies (except the rawline -rectified source) are isolatedfrom the power line.

M10 module number 9-160 is thelargest plug-in module in the newZenith line of System -3 color TVreceivers. M10 contains the ac -line -

rectified non -isolated power supply(Figure 1), one isolated dc -voltagesupply for startup of the horizontal,an overvoltage-shutdown safety cir-cuit, an IC that varies the drive -pulse width for sweep regulation,two horizontal driver transistors,components for sweep -linearity andpincushion correction, and a high -voltage transformer with several ad-ditional windings that feed rectifiersto produce several isolated low

voltage power supplies.Although M10 modules are in-

cluded in all System -3 models, thehigh voltage and other voltages arenot the same in all. This requiresseveral changes of componentvalues along with accompanyingvariations of module numbers. M10numbers used for the 1981 Zenithline include 9-160-03C, 9-160-05,9-160-06 and 9-160-03D. The sam-ple receiver used during this series


RUT

120 V AC

COLD

FX3376

24

SPARK GAP

TX3376

C3375

2200

SI

POWER

0

RX3676

PTC

C3376

.004/

L3356

RX3377

I.2M

ZENITHM10 POWER

FX3326

- 125 mA

TX3351CRX3333

CX33268

300 pf

CRX3331

1133514.2

RX3327

TT 10 A

R13326

100Kff

1..:11

1.X3330

CRX3331 330 1,f I

1600 SUPPLY

CX3326A

30011f

CR3376

GATE

CR3352

GATE

TO + 25V

SUPPLY

+160SOURCE

,START UPI

TO 4 190

AT Q3152

COLLECTOR

Figure 2 These are the only M10 power supplies that operate from 120Vac line voltage. Notice that the 120Vac wiring isinsulated from all grounds, and that the + 160V supply is not connected to cold ground. Hot grounds are indicated by thetriangular symbol. The + 160V supply provides power only for the horizontaloutput transistor, while the isolated + 16Vsupply provide startup voltages. A convenient point to measure the + 160V supply voltage is across RX3326. Late -productionmodules have a spark gap across RX3377 to prevent circuit damage if the HV transformer fails.

has a 9-160-05 M10 module.Therefore, voltages and resistancevalues in a few areas are slightly dif-ferent than those in other modules.

Line -voltage rectificationThe Figure 2 schematic shows

components and wiring of the twodc -voltage supplies that operatefrom line voltage. The CRX3327-through-CRX3330 bridge rectifi-er provides about + 160Vdc with120Vac line voltage at average pic-ture brightness. This voltage rises toabout + 170V if any defect removesthe current normally consumed bythe horizontal -output stage. Failureto start up removes all dc voltage ex-cept the raw voltage, now + 170V.A defect in the + 16V supply, suchas a shorted bridge diode or an openFX3326 fuse, produces these symp-toms. Raw rectified voltage can beeasily checked by connecting the dc -voltmeter lead across 100K resistorRX3326, located near the module'sedge at the left of fuse FX3326.

Caution: The corner of M10shown in Figure 1 has several com-ponents and wires that are con-nected to line voltage. To protectboth equipment and technicians, it

Figure 1 This corner of the M10 modulehas two line fuses and othercomponents of the + 160V non -isolatedpower supply and the + 16V isolatedstartup supply. Both sides of the+ 160V supply measure about 55Vac toearth ground, so care must be used toprevent shocks to people or damage totest equipment.

is recommended that an isolationtransformer be added between thewall plug and TV power cable. Eventhen, care should be used whenmeasuring anything in this area.

Notice the triangular symbol usedseveral times in the Figure 2schematic. It indicates a hot groundfor the + 160V non -isolated powersupply. The same triangular symbolalso is used around the horizontal -output transistor, the yoke andflyback return paths, and a fewothers.

The + 160V non -isolated powersource has no regulation. Its onlyload is :he horizontal -output tran-sistor where regulation occurs.

Ac -line power is applied to theprimary of transformer TX3351(Figure 2), but the secondary wind-ing and the remainder of the + 16Vsupply is referenced to cold ground(conventional ground sumbol).Startup requires the + 160V supplyand the isolated + 16V supply.

When the TV switch is turned on,dc power from the + 16V supplyflows through forward -biaseddiodes CR3376 and CR3352 to twovoltage sources that supply thehorizontal -drive stages. Because theQX3326 horizontal -output tran-sistor has normal collector dcvoltage from the + 160V supply, thestart of base drive at QX3326 allowsthe horizontal sweep to begin fulloperation. This sweep operationbrings normal voltage to the + 25Vand + 19V supplies, which reversebiases CR3376 and CR3352 so theybecome open circuits that discon-nect the + 16V startup supply. ThusCR3376 and CR3352 operate asvoltage -controlled switches duringthe startup procedure.


Power supply

+16 V STARTUP

HOW DRIVE

FROM 3C-3

dRX3301

II V

13304

1000

R3320

1000

+0.41 V

C3301

4700 PR 7- 1.3V PP

13305 13307

1800 2200

RX3314

1a)o

-6.3/

+6.4 V

C3305 -I 22Oµ1

1CX3301PULSE -WIDTH MODULATOR

C3304

.322 T

4 +6.1V . wY3

5 V PP

5 +11.94+4V9.2VPP

13315==+12 IA1 -www--t

moo

U3301 6200B3316 C3307

4700 .39

R3313

6800

PULSE WIDTHMODULATOR

RX331

C3309 IDA: I

FACTORY SEALED

10K

191001

RX3312

R03310

C33% 1.0033

=R34(.4

47K

8200

RX3309

IOK

1.6 V PP

WS

8+0.720

+19V

SUPPLY

1+18.W1

+12V

R3302

680

70 V PP

POS PALSES

5.1 V PP

13463

e---.4711

SHUT DOWN

CR3354

0.2V PP

VZ7

R3131 - I.6V CR3337

C3347 -I-

W6

-0.16QX3338

SHUTDOWN

+ 11.9 V

R03333

21K

+:L9 V

RI

+12V

CR3353 RX336170 VPP

POS PULSES \ 1100+ 52V

C3351

0.1 T

1000C3339

R13360 4.7µF

2743103366

C3352

2.21IF

I

RX3365

'AA.27K

M10 PULSE WIDTH

56K

1013359

1100

4700

RX3358

2200

CRX3355

12V

+ I7V

RX3363

181(

RX3362

620

CX3341

1 lir

-0.C5 V

C3346

of

RX3357

72

CR3356

4V PP

QX3351

SHUTDOWN

- 0A2 V

11113335

270

SW

TO BASE OF Q3301

FORWARD HORIZ

DRIVER

ON M10

9-160-05

RX3334 -1 V FROM BRIGHTNESS

LIMITER1500

Figure 4 Circuitry around ICX3301 is for the pulse -width function of sweep regulation. The shjtdown circuitry with QX3338and QX3351 makes up a positive -feedback switch (similar to an SCR) that kills the horizontal drive at ICX3301 pin 1 whenovervoltage or overcurrent occurs. Notice that the base of QX3338 is connected to the collector of QX3351, while the base ofQX3351 is connected to the collector of QX3338. If supplied with forward bias and coupling capacitors, the circuit would bea multivibrator oscillator. Voltages and waveforms were recorded when the picture had ncrmal levels of brightness andcolor. (Waveforms W7 and W8 are not impolant.)


Pulse -width regulalion1CX3301, which varies the drive

pulse width, is located at the rearedge of M10 module (Figure 3).ICX3301 performs several func-tions. It amplifies the horizontalsquarewave signal coming from thecountdown circuit on the M2module to ICX3301 pin 7, with theoutput signal appearing at pin 6.This squarewave signal is filtered toproduce a triangular waveshape atpin 4 (Figure 4 schematic).

A factory -adjusted RX3312 con -

Figure 3 Pulse -width modulatorICX3301 (top arrow) is mounted behindthe QX3326 output transistor (on heatsink). The lower arrow points totransistors QX3338 and QX3351 of theshutdown circuit. Other shutdowncomponents are nearby.

Figure 5 This backside view of the M10module shows ICX3301 (left arrow),factory -adjusted control RX3312 icenterarrow), and 03301 forward horizontaldriver (arrow at right).

trol adds a certain dc voltage to thepin 4 triangular waveshape, and thiscombined signal is compared insideICX3301 to a dc voltage at pin 3that varies with line voltage and the+ I9V supply. The comparisondetermines the duty cycle of thedrive signal exiting from ICX3301 atpin 1, and the duty cycle in turndetermines how soon during eachhorizontal cycle the horizontal -output C/E current begins to flow.The current is eliminated at thesame point of each cycle. Therefore,more output transistor power is ob-tained when the conduction occursearly in the cycle, while lower powerresults from a later beginning ofC/E current.

Waveforms and dc voltages inFigure 4 were measured during nor-mal brightness. ICX3301 is near theleft in Figure 5, and driver transistorQ3301 is at the right.

Figure 4 also has the shutdownsafety circuit with transistorsQX3338 and QX3351. Flybackpulses are rectified by diodeCR3353, producing about + 52V,which is filtered by RX3361 andC3352 before it is applied to afactory -selected voltage divider(RX3360, RX3366 and RX3365 astop leg, with RX3359 and RX3363as lower divider leg). Various valuesare used in other 9-160 modules, sothese are correct only for 9-160-05

modules.Output of the voltage divider is

about + 12V, which is applied tozener diode CRX3355 (12V rating).Zener CRX3355 has no significantcurrent, so the QX3351 base voltageis about zero. Actually it measuresslightly negative, because diodeCR3337 rectifies the small -amplitude pulses at its cathode.

The QX3351 emitter has .a smallnegative voltage coming from thebrightness -limiting circuit at the lowend of the high -voltage winding.QX3351 has approxomately zeroB/E bias and, therefore, has no C/Ecurrent.

Transistor QX3338 has + 12V atits emitter and + 11.95V at the base.Because it is a PNP type, this is for-ward bias, but only about-0.05V; far too small to cause C/Econduction.

During normal operation withoutshutdown, QX3351 and QX3338 areinactive. But notice that the QX3338base is fed through RX3333 fromthe QX3351 collector, while theQX3351 base is connected to theQX3338 collector through RX3358.The circuit is a regenerative switchwaiting to be triggered.

If increased pulse amplitude atCR3353 raises the QX3351 positivebase voltage or the picture -tube cur-rent increases above normal anddrives the QX3351 emitter morenegative, QX3351 will be forwardbiased. QX3351 conduction reducesits collector voltage, which in turnforces the QX3338 base voltage to aless positive voltage. This is forwardbias for QX3338, so it draws collec-tor current, thus producing apositive collector voltage. Thepositive collector voltage passesthrough RX3358 to the QX3351base, where it increases the forwardbias. Increased QX3351 conductionin turn increases the QX3338 con-duction, and so on. The end result issaturation of both transistors.

Perhaps you recognize theprevious action as a regenerative orpositive -feedback dc switch whicheither is open (neither transistordrawing current) or closed (bothsaturated). After this switching isactivated, it continues until power isremoved, including power loss fromshutdown.

When shutdown switching oc-curs, the QX3338 collector hasalmost + 12V (from emitter) whichtravels through diode CR3354 to pin7 of IC3301 and through R3331 and


Power supply

R330

C3302

--11-180 pf

C 3308

R3302

680

+ 12 V

47

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0.9V PP

0.42vC3303

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+23.8V

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+ 24.1 V

IC3335022 -

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R3329

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C3338

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R3330

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TX3326

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-3.58 REVERSE83328

.3047

1608 PP

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13C -5I

110-2,

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R3353

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ZENITH HORIZ SWEEP

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ON M10

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W11

Figure 6 Measured dc voltages and peak -to -peak waveforms are shown on This schematic of the horizcntal-output stage onthe M13 module. ALI waveforms have the same phase except 111,15 and 1/V16, which are at vertical rate, and werephotographed with a normal picture of moderate brightness. Many of these waveforms change with brghtness and linevoyage variations.

4ns

CR3337 to pin 8 of ICX3301. TheIC then eliminates the pin -1 basedrive that is amplified to drive thehorizontal -output base. Therefore,the horizonal sweep is eliminated bythe shutdown operation. Indirectly,this also stops all sound and picturefunctions, because the sweep signalpowers many low -voltage supplies.

When power is turned off for ashort time, the + 12V that maintainsthe shutdown condition disappears.Switching on the power activates thestartup cycle, bringing horizontalsweep and operation of all scan -rectified power supplies. If theproblem causing the previous shut-down is now gone, the receiveroperation can be normal. Any re-maining overvoltage or overcurrentconditions, however, will produceanother shutdown.

Horizontal drive and outputThe schematic in Figure 6 has im-

portant waveforms and voltages forthese stages: forward and reversehorizontal drivers; output tran-sistor; regulator (chopper) com-ponents; yoke and pincushion -correction components; andprimary wiring of the high -voltage(flyback) transformer.

When the schematics werechecked against the actual modulewiring, several mistakes were found,both in the Zenith schematic and asimilar Photofact. (No Photofactfor Zenith SM1973P has been re -

Figure 7 On the M10 module behind the high -voltage transformer are theseimportant components: CR3307 damper diode (arrow at far left); TX3301 regulation(chopper) transformer (second arrow from left); CR3306 pulse -switching diode(third from left); and sweep -tuning capacitor CX3316 (at far right).


Power supply

leased at this writing, but 1966-2 ap-plies to many sections.) ThePhotofact, for example, showed theusual cold -ground symbol ratherthan the triangular hot -ground sym-bol for C3350, C3314 and CX3320.Also, the polarity was reversed for

Figure 8 High -voltage transformerTX3352 has internal rectifiers. Focuscontrol is mounted above the HVtransformer.

Figure 9 Before the M10 module can beslid out of its mounting tracks, thesetwo parts must be removed. Thebracket (at top) is bolted to the focus -control mounting and the cabinet'smain framework. The key (below) mustbe rotated and pulled upward toremove it from the module.

diode CRX3335 in the reverse -driverstage.

Notice that Figure 6 waveformsare referenced against two grounds.All are referenced to cold groundexcept W7, W8, W9, W10, WI I,W13 and W14 which have the scopeground connected to hot ground.Remember the safety precautions:Use an isolation transformer for thereceiver ac power, or float the scopefrom earth ground (not recommend-ed except for emergencies).

Although a conventional generalsequence of driver, output transistorand yoke/flyback is followed inFigure 6, the details show manyvariations from past circuits.

Two driver transistors are re-quired for starting the QX3326output -transistor C/E conductionsooner or later in each horizontalcycle. QX3301 forward driver isshown in Figure 5 and QX3326reverse driver is shown in theoverall -location photograph. Thisadjustable output current is the firststep of regulation, but a specialchopper transformer, TX3301shown in Figure 7, and two switch-ing diodes in the output -pulse circuitalso are required.

Figure 8 shows the TX3352 high -voltage (flyback) transformer withthe focus control mounted above.Four diodes for focus and highvoltage are integrated with the high -voltage windings.

Figure 10 This is the television'sappearance after the M10 module isremoved, wired to the edge connectorsand placed on top of the frameworkabout 3 inches to the rear of the formerposition. Many tests andmeasurements can be made while themodule is in this position.

Testing the M10 moduleAs described in previous articles,

Zenith module MI or M2 car. betested with full power and undernormal conditions by removing theedge connectors, sliding the moduleout of its mounting grooves, andthen reinstalling the edge connectorswhile the module is hanging behindthe receiver. Cable lengths are suffi-cient. This is not necessary withmodule M5, because it usually canbe tested without removal from thepicture -tube socket.

Unfortunately, this method wasnot successful when tried with theM10 power -supply module.Removal of the edge connectors andone metal bracket (near the flyback)

did not allow the module to be slidbackward out of the mountinggrooves. That was the first snag. Itwas solved by the friendly Zenithservice manager who described aplastic key (Figure 9) near the 3Nsocket. After the key was rotated90° and lifted up out of the hole, themodule could be slid out of thegrooves.

But the only position of themodule that allowed all cables andedge connectors to be reinstalledwas on top of the plastic frameworkand about 3 inches farther to therear that it originally was (Figure10).

The new position allowed manytests to be made on the M10 cir-cuitry, although the space remainedcrowded.

Use of a 6 -inch insulated -hooktype of probe (such as the PomonaMaxi Grabber) is highly recom-mended. With the ac power off,connect the long probe to thedesired terminal with the other endof the test lead connected to meteror scope. After all connections aresecure, the power is turned on andthe measurement made. Then thepower is turned off while the testprobe is removed. Use this methodfor each individual measurement.Often a reading can be made beforethe picture tube warms enough toshow more than a soft faint picture,so little time is wasted.

Measuring IC voltages can be dif-ficult unless a test clip (such as aPomona Dip Clip) is used to bringeach pin's voltage and signal up topins at the clip's top. Alternately, atest lead can be connected to someresistor or capacitor wire that inturn contacts the desired IC pin.

Above all do not allow any shortsbetween wires or pins. It's possiblefor a split-second short to ruin manyICs or transistors.

Also, observe the precautionsstated previously about the hotgrounds and other dangerouspoints.

Zenith flatly states in a bulletin:"In the event of a failure involvingthe M10 module, exchange it; donot try to repair it in the customer'shome." This admonition has theforce of law for warranty repairs,but it probably is a wise procedurefor most out -of -warranty repairs aswell. One strong reason is the dif-ficulty in finding all the test pointsand components while the module isin the cabinet.


B

Vc c

-0 X EQUIVALENT RTL NORGATE SCHEMATIC

NOR GATE LOGIC SYMBOL

Figure 2

V c c

EQUIVALENT DTL NANDGATE SCHEMATIC

A)°B

NAND GATE LOGIC SYMBOL

Figure 3

output

A

B

SIMPLIFIED TTL NAND GATE SCHEMATIC

output

A

B

MULTIPLE EMITTER TRANSISTOR TTL NAND GATE SCHEMATIC

Figure 4


Digital ICs

the output can supply logic voltageto 10 gates.

RTL circuitsResistor -Transistor -Logic (RTL)

ICs are usually designated by series9900 chips. RT Logic was theearliest form of solid-state logic,consisting of direct coupled tran-sistors and resistors. RTL circuits

are primarily constructed as NORgates.

Most RTL chips come in the 8- or10 -pin H package, which is theround transistor -like package shownin Figure 1. With the 8 -pin chips,pin 8 is usually Vcc and pin 4 is thereference. With the 10 -pin package,pin 10 is usually Vcc and pin 5 is thereference.

vcc

o output

TTL NAND GATE WITH SCHOTTKY DIODES AND TRANSISTORS

SCHOTTKY TRANSISTOR SCHOTTKY DIODE

Figure 5

TTL NAND gate withSchottky diodes andtransitors

Figure 6

Basic CMOS invertercircuit

input

VDD

jP- channel

output

N- channelha-

The required supply voltage islow, usually about 3.6V. Logiclevels require 1V for a high level andless than 0.4V for the low level state.

RTL chips usually do notamplify. They are characterized byslow switching speeds because ofsaturation, and a low level of noiseimmunity, meaning they are easilytriggered by noise. Fan -out is about5, and anything more causes thehigh logic output voltage to droprapidly. The main advantage ofthese chips is that they are simple tomanufacture and require only asingle supply voltage.

The RTL chip also has the disad-vantage of being a "current sourc-ing" type circuit, which means thatthe gate trigger must supply currentto forward bias the input gate tran-sistors. This describes the modeneeded to activate the gate.

The equivalent circuit for a basicRTL NOR gate is shown in Figure 2.

RTL chips are available as NORgates, buffers, shift registers, typeD, T and J -K flip-flops, invertersand adders. A survey of partscatalogues reveals that the RTLchips are on their way out. RTLchips, although still in use, arerapidly being put to pasture bynewer chips.

DTL circuitsThe Diode -Transistor -Logic

(DTL) family is based on the NANDgate. The DTL family of ICs aredesignated by 9000 series and 9930to 9963 series by most manufac-turers.

The DTL chips are manufacturedin the type A, B or N, with 14 and 16pin DIP configurations. With the14 -pin chips, pin 14 is the supplyand pin 7 is the reference. With the16 -pin package, pin 16 is the supplywhile pin 8 is the reference.

The DTL chip requires a 5V sup-ply and logic levels the same as forthe RTL chip, i.e., high level equals1V, low level is less than 0.4V.

DTL chips provide gain, and be-cause diodes are used in the circuit,faster switching speeds and a slight-ly higher noise immunity is realized.DTL circuits operate in the "currentsinking" mode, which means thatthe forward current necessary to ac -


tivate the gate transistors is suppliedinternally. Fan -out for this type oflogic is usually a maximum of 8.

Figure 3 shows the schematicequivalent circuit for the basic DTLNAND gate. QA is an emitterfollower with the base -emitter junc-tion always forward biased. This inconjunction with D3 sets the voltagelevel which a noise pulse must over-come to falsely trigger the gate,thereby providing a higher noisemargin than the RTL circuit. QBacts as the inverter for the NANDfunction and also providesamplification.

In addition to the NAND gate,DTL chips are available as ANDgates, OR gates, hex inverters, R -Sand J -K flip-flops, exclusive ORgates, quad latches and monostablemultivibrators.

Like the RTL chips, DTLs areused less frequently because newertechnology is pushing them into thebackground.

TTL circuitsThe Transistor -Transistor -Logic

(TTL) family is also based on theNAND gate. The 'TTL family (alsocalled T2L) of ICs are designated bythe 5400 or 7400 series chips, themost commonly used.

The TTL chips are manufacturedin the same A, B or N, 14 and 16 pinDIP layouts as the DTL family, andthe same pin connections for supplyand reference.

The supply voltages and logiclevels required for TTL chips areabout the same as for the DTL ICs.Fan -out for the typical TTL chip isusually about 10.

TTL circuits are characterized bymultiple emitters on the input gatetransistors. The TTL transistorswithin the IC could be considered astwo or more transistors with theirbases and collectors wired togetherto form the basic NAND gate(Figure 4). TTL circuits also operatein the "current sinking" mode.

'TTL chips are available in almostevery type of digital logic circuit im-aginable and are carried by nearlyall the major electronic componentdistributors.

Schottky diodesA whole new family of TTL ICs

was developed with the advent ofthe Schottky Barrier Diode. The ad-dition of the Schottky diodes to theTTL configurations increases theswitching times of the TTL circuitsby decreasing the transistor turn-offtimes. The Schottky diodes preventthe transistors from operating insaturation.

Schottky ICs are designated by54S/74S or 54SL/74SL series ICs.Packaging is the same as for TTLICs.

The supply voltage requirementsfor Schottky ICs are more criticalthan normal TTL circuits. The sup-ply voltage range is limited to 4.5 to5.5V. Noise immunity and fan -outare slightly better than the standardTTL circuit. Switching times are ap-proximately one-third that of thestandard TTL circuit. Figure 5

shows the TTL NAND gate with theaddition of both Schottky diodesand transistors.

Schottky ICs are usually availablein the same circuit configurations asthe TTL ICs, although at a slightlyhigher price.

MOS and CMOS ICsBoth MOS and CMOS ICs are

based on the Field Effect Transistor(FET) instead of the junction tran-sistor. In MOS transistors, an in-sulating layer of oxide is positionedbetween the metal gate of the FETand the semiconductor siliconmaterial. Thus the name Metal -Oxide -Silicon, or MOS.

The advantages of this process aresimpler fabrication of Large ScaleIntegrated circuits (LSI) and lowerpower losses. The main disadvan-tage of MOS ICs is that they requireboth positive and negative powersources.

This disadvantage was overcomewith the development of CMOS de-vices. CMOS devices simply useboth P and N channel FETs to forma Complementary MOS or CMOScircuit. Both MOS and CMOSdigital ICs differ from the otherdigital ICs in that the basic circuit isnot derived from a gate but from aninverter. As with the gates, all otherlogic circuits can be constructedfrom the basic inverter.

MOS and CMOS ICs are desig-nated by 4000 or 40,000 series chips,

and are produced in 14, 16 or 24 pinDIP style packages. Vdd is the labelgiven to the positive supply whileVss is the reference lable. Vdd isusually the last pin (14, 16 or 24)while the reference is the half -waypin, i.e., 7, 8 or 12.

Supply requirements allow mostMOS and CMOS chips to operatebetween 5 and 18V. Logic inputlevels are not specified as they arewith TTL chips. Instead, manufac-turers data lists a Voltage TransferCharacteristics curve, because thelogic levels will depend upon whatsupply voltage is used. For many ap-plications, however, a logic highstate is 5V while the low state is zerovolts, using a 5V supply.

CMOS chips provide gain, have ahigh noise margin (typically 1 V orgreater), and have switching timesrated in nanoseconds (10-9). Fan -out is 50 or greater when feedingother CMOS circuits. The discreteequivalent circuit for the basicCMOS inverter is shown in Figure 6.

CMOS chips require specialhandling due to their extreme sen-sitivity to static electricity. Thetechnician must be more conscien-tious with CMOS circuits, but themany advantages of CMOS ICsmake their use attractive in spite ofthe tricky handling required.

ECL ICsEmitter -Coupled -Logic (ECL),

although it provides the fastestswitching speeds possible, also re-quires relatively high operating cur-rents. The high current draw ofECL circuits makes it difficult topackage this type of logic in ICs.ECL chips are usually specializedand not commonly available unlessthey are in-house parts manufac-tured by the larger corporations fortheir own equipment. ECL chipsmay be found primarily in largecomputers.

HTL ICsHTL or High -Threshold -Logic is

a specialized form of the DTL cir-cuit. HTL circuits employ a zenerdiode and an extra transistor to pro-vide an extremely high noisemargin. HTL chips are used inspecialized applications and havelimited appreciation. El


producipoll

.1 -

INN .,

zt^0 *Du,

WILT

a

Digital multimetersA. W. Sperry Instruments Inc. an-

nounces the introduction of twonew digital multimeters-the AWS

The two units feature fullmeasurement capabilities - ac/dcvolts, ac/dc mA and ohms-plus a10A ac/dc range. A 5 -year limitedwarranty accompanies both units.

Features include autoranging onvolts and ohms, 31/2 -digit display,10mm-high numerals, automatic in-dication of units and signs,autopolarity, overrange indication,safety fused on ohms and mA, lowbattery warning, audio tone con-tinuity buzzer (EZ-6110), normaland low power ohm ranges, rangehold (EZ-6110), shock -resistantABS plastic housings, pocket size,and up to 300 hours continuous use.Ranges are Vdc 0-200mV, 2/20/200/1000; Vac 0-2/20/200/600; ac/Adc 0-10; ac/dc MA0-20/200; ohms 200/2K/20K/200K/2000K; low power ohms0-2K/20K/200K/2000K.

Units come fully equipped andready to use with safety test leadsand special clip for 1 -hand leadoperation, and with batteries andfuse installed plus one spare. ModelC-30 Ever -Ready carrying case isoptional.

We regret that A.W. Sperry was inadvertent-ly omitted from the July 1981 digitalmultimeter roundup.


Home satellite TV productsDownlink Inc. has announced

two home satellite TV products, theSkyview IV parabolic antenna andthe Skyview IV system.

The Skyview IV is a lightweight,11 -foot fiberglass parabolic antennadesigned for low-cost shipping, ex-pandability and ease of operation.The dish is constructed in four sec-

tions, so it can be easily shippedanywhere or transported by pickuptruck. It is expandable to 13 feet (4meters) by adding extender panels.

No training or special tools are re-quired for assembly and installa-tion. Installation requires only asimple 3 -foot -square concrete padand four holes.

The antenna has better protectionagainst the wind (125 -mile -load sur-vival rating), rough handling andweather than conventional alumi-num construction. The antennaweighs 400 pounds, includingmount.

The antenna is also easy tooperate. It can be shifted fromsatellite to satellite with a hand -crank adjustment, and can receiveall North American communica-tions satellites.


Integrated circuit toolsThe XD series of extraction and

insertion tools has been introducedby Xcelite for efficiency and preci-sion operations on integrated cir-cuits.

The series includes eight insertion

tools of aluminum and stainlesssteel construction with varying pincapacities featuring an adjustment

for IC tolerance variations. Theselong wearing tools are safe for MOSand CMOS devices and insertwithout stress on lead seals.

The 1 -hand XD -16 extractor re-moves 4 to 48 pin DIPs, will notbend leads, and eliminates the prob-lem of flying solder.

Individual tools are packaged invinyl hang-up pouches imprintedwith use instructions.


Earth station modulatorBlonder -Tongue Laboratories

Inc. has available an earth stationmodulator designed for operationwith Television Receive Only(TVRO) satellite terminals wherethe audio and video are provided asseparate base band signals. TheESM-4928 is available for VHFchannels 2-13 and Mid Band chan-nels A -I.

The modulator is a vestigial side -band audio/video modulator withextremely accurate crystal -con-trolled visual and aural carriers thatminimize color beats and audiodistortion. The unit has a calibratedvideo modulation meter and a truepeak -reading LED audio overmodu-lation indicator to ensure precisemodulation control. The audio in-dicator permits adjustment for op-timum sound quality.

A video low pass filter in theESM-4928 rejects unwanted subcar-rier frequencies of secondarysatellite services, preventing adja-cent channel interference.



PhotofitiCITEKChassis ECC-20341 2012-1

CURTIS MATHESChassis CMC82-1/2/4/5/6/7 2018-1

PANASONICChassis GP80Y,YR 2004-2

PHILCOChassis A22-2 (Code 01/02, Run 01 thru 08) 2013-4Chassis GP80Y, YR 2004-2

RCAChassis KCS204BF,BH,BD 2012-2Chassis CTC108A (Sub 1, Sub 2) 2012-4Chassis KCS204H,J 2013-1Chassis CTC107A (Sub 1) 2013-5

SAMPOChassis CS -19T 2017.1

SANYOChassis A2T-77N00 2013-2Chassis A2T-72001 2013-6

SEARS317.23990050 2014.3564.42010050 2015-1564.48260050/51 2016-1

SHARP19E75 2014-1IT-25UA (MONITOR) 2015-3

SONYTV -515 2014-2Chassis SCC-319A-A 2018-2

TEKNIKA/CITEKChassis ECC-14142 2013-3

TEKNIKAChassis ECC-20339 2015-2

WARDSGGY-12961A/971A 2012-3GEN-11770A,B,C 2016-2Chassis AB -C 2017-2

ZENITHR476W 2004-3Chassis 22MB1X 2016-3R476W 2004-3

reader's mniimNeeded: Scott stereo model #2560 service manual. Willcopy and return. S. Rosenzweig, 2818 W. 8th St.,Brooklyn, NY 11224.

Needed: Schematic and service data for a Bomanmodel TC-9-MK2-FM (AM -FM) auto radio. MaxFriedman, 81-47 260th St., Floral Park, NY 11004.

Needed: 820 or 830 B&K capacitor tester, CK3000Sylvania test jig. State condition and price. Phi/Schrock, 84343 Hilltop, Pleasant Hill, OR 97401.

Needed: Sencore model #YF33 ringer, variable linevoltage transformer 0 to 120V (5A), and Philco powertransformer for stereo #H1714. D. Bernard Fritz, 3210St. Lawrence Ave., Reading, PA 19606.

Needed: Audio IF coil, Magnavox part #36B043-6,used in Magnavox TV chassis T 932. Norm's TV, 79Pond Road, Lewiston, ME 04240.

Needed: Complete chroma board PC unit PW329Cpart #23141204 for Toshiba TV model C7A NLA. J.Hofslund, 1011 S. 10th St., Manitowoc, WI 54220.

Needed: Remote control unit and information forPhilco radio 39-116. Also need Sam's tape recordermanual TR19. James Humphrey, CET, Room 212,1006 E. 28th St., Los Angeles, CA 90011.

Needed: Model 465 B&K CRJ tester. Reasonableprice. H. D. Stevens, 31 Second St., No. Arlington,NJ 07032.

Needed: 24 DP4A, 16 CWP4A and 17 CFP4 B&W pic-ture tubes. Joseph J. Mehalko, 324 4th St., Blakely,PA 18447.

Needed: One high wattage isolation transformer. Willtrade good, used Sencore CRT checker, model CR143.Mike's Repair Service, P.O. Box 217, Aberdeen Prov-ing Ground, MD 21005.

Needed: Power transformer for Webcore model WFX257 stereo, part number 710001A. Sam's number forstereo is MHF-39. John Osborne, Winthrop Elec-tronics, Town Hall Lane, Winthrop, ME 04364.

Needed: RCA workshop manuals 1 through 18, andother troubleshooting tips. Calvin Logue Jr., 923Washington Rd., Westminster, MD 21157.


Wanted

ramarketalace

Advertising rates In the Classif ad Section are 35cents per word. each insertior, and must beaccompanied by cash to Insure publication.

Each initial or abbreviation counts a full word.

Minimum classified charge $3 00

For ads on which replies are sent to us forforwarding (blind ads). there Is an additionalcharge of $3.00 per Insertion to cover departmentnumber, processing of replies, and mailing costs

Classified columns are not open to advertising ofany products regularly produced by manufactur-ers unless used and no longer owned by themanufacturer or distributor.

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Does businessstress causehigh bloodpressure?

Stress on the job is a realproblem for most of us.Many people think high-pressure jobs cause highblood pressure.

Scientists and doctorsaren't sure if stress causeshigh blood pressure. But, onething is for sure: anybody.no matter how they react tostress, can have high bloodpressure.

If you have high bloodpressure, you can controlit -with medication, weightcontrol, less salt, andwhatever else your doctortells you to do, every day.

No matter what you do fora living, keep on living.

High blood pressure.Treat it and

National High Blood Pressure Education ProgramNational Heart. Lung and Blood Institute.

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Electronic Servicing

Advertising Sales offices

NATIONAL SALES MANAGERGreg GarrisonP.O. Box 12901,Overland Park, KS 66212Phone: (913) 888-4664

LONDON, ENGLANDJohn Ashcraft 8 Co.,John Ashcraft12 Bear St., Leicester SquareLondon, WC2H 7AS, EnglandPhone: 930-0525 Telex: 895-2387

AMSTERDAM, HOLLANDJohn Ashcraft 8 Co.,John J. LucassenA kerdijk 150A1171 PV-Badhoevedorp, HollandPhone: 0-2968-6226

TOKYO, JAPANInternational MediaRepresentatives, Ltd.2-29, Toranomon 1-chome,Minato-ku. Tokyo 105. JapanPhone: 502-0656

NORWOOD, AUSTRALIAWilliamson 8 AssociatesJohn WilliamsonNo. 2 Edmund St.Norwood. S.A. 5067, AustraliaPhone: 42-7074


For the man that would rather fix it himself

Technical Publications hasservice manuals designed for you!SES-13 Small (Air Cooled) Engines Service Manual. $9.95(336 pages). You can service your own engines onlawnmowers, tractor sprayers and other power equip-ment. Special section on fundamentals, troubleshooting,preventive maintenance. Step-by-step instructions.

WLMS-1 Walking Lawnmower Service Manual $7.95 (128pages). The complete guide to the care and repair of yourwalk -behind, push -typediagrams.

CSS-6 Chain Saw Service Manual. $8.95 (over 300 pages).Here's everything you need to know to tear down, repair,reassemble and adjust most popular chain saws. A trulycomplete chain saw manual.

GSM -1 Small AC Generator Service Manual $7.95. A brandnew manual that contains maintenance, service andtroubleshooting procedures, as well as wiring schematicsfor most generator models. Covers electrical powerp antsunder 8kW that generate alternating current and aredriven by air cooled engines.

OS1-8 Outboard Motor Service Manual Volume 1 58.95Covers motors below 30 hp.

0S2-8 Outboard Motor Service Manual Volume 2 $8.95(232 pages). Covers motors with 30 hp and above. BothVolumes 1 and 2 provide detailed funcamentals onperiodic servicing.

Put these books to work on your own equipment...(Or service outside equipment for profit!)

Small (Air Cooled) Engines Service Manual Walking Lawnmower Service Manual Chain Saw Service Manual Small AC Generator Service Manual Outboard Motor Service Manual (Vol 1) Outboard Motor Service Manual (Vol 2)

Remittance must accompany orders of less than $25.00.Postage paid when payment accompanies order. Allow fourweeks for delivery.

How tD send money: The best way to send money is yourown personal check, post office money order, expressmoney order or by bank draft or check. DO NOT SEND CUR-RENCY OR STAMPS.

Check Money Order EnclosedShip C.O.D. (No C.O.D.s outside of U.S.)

Missouri and Kansas Residents add 4% sales tax.Tennessee Residents add 6% sales tax.

Write for a free catalog covering our entire line of servicemanuals and wheel -type tractor service manuals.

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TechnicalPublicationsDivisionIntertec Publishing Carp.P.O. Box 12901, Daps. ESOverland Park, KS 66212(913) 8884664

aline of antennas as strong as itsin time for your peak selling season

name

Transmission LineTerminationbleeds off staticcharges thruantenna systemground. Terminalstub improvesfront to back ratioon lower channels.

Wide Spaced,Heavy Duty FeedLines help preventshorting fromheavy build-upsof snow or ice.

Aluminum Con-struction of allkey metal partsworks to elimi-nate rusting -provides long life.

Golden -ColorAlodine Finish isconductive-helpsimprove electricalperformance!

Dual IsolatorBars insure noloss of UHF toVHF signal trans-fer. (Combinationmodels only.)

High -ImpactPlastic Insulatorsdouble -lock eachelement to theboom for extrabracing anddurability.

Strain ReliefInsulator accom-modates either300 OHM twin -lead, Foam lead orCoax downlead.

FM Block reducesFM gain up to12dB. Remove toreceive full FMgam.

U -Bolt Mountingprovides a largerclamping area ,larger locking nutwith teeth anintegral partassures a morerugged U -BOLTarrangement.

Corner ReflectorBracket enlargedand re -locatedin most models.

Optional Breakaway UHF WingDirectors providemaximum gainof standard UHFchannels withoptional coverageof Hi UHF channelsand translatorfrequencies whenbroken off.(Combinationmodels only.)

Zenith Dipole cmUHF.(Combinat onmodels only.)

ElectricallyMatched Termi-nals With StainlessSteel Screwseliminate mis-match... protectagainst rusting,and providepositive electricalcontact withimproved no -stripstainless steelserrated washersfor the take offterminals.

Zenith has quality easy -to -install antenna kits-UHF only,VHF YAGI and Stereo FM antennas as well as a complete line of

reception aid equipment. See your Zenith distributor for news of hisexciting money -making Fall programs and Catalog No. 902-2019!

II

VHF/UHF/FM Model 973-217illustrated. Chromatenna II

comes in seven combinationVHF/UHF/FM...six VHF/FM models.

VHF ColinearDirectors provideextra signalboost on bothlow and highband VHF.

Proximity SpacedSignal Balancer(Z elements)provides automat-ic taper controlof periodic driver,improves imped-ance matchingand signal level-ing on both Loand High bandchannels. Im-proves Channel 7pattern.

Loading Straps-metal plates closeto first VHFelement insulatorsprovide compensation for Lo andHigh band bytuning the firstdriven elementwith extra capacity.

Sleeved Elementsof heavy-dutyconstructionafford extrabracing andprotection.

70, "TA

Rugged 1" SquareBoom providesextra strengthcompared tomany round -typebooms.

Hi -Bracket withangled ends foradded strength.

The quality goes In before the name goes on*

Zenith Radio Corporation/Service, Parts & Accessories Division/11000 Seymour Avenue/Franklin Park, Illinois 60131


$47,1t,y i i i i ti - worldradiohistory.com...editorial, advertising and circulation cor-respondence...

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