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Tips, Tricks & Gadgets


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  • Tips, Tricks & Gadgets

    This page includes "Secret Tips, Tricks and Gadgets" from our associated electronic repair technician network. Most ofthese have been submitted by members of our ELREPAIR-L email discussion groups. but are available to all.

    If you have a favorite TIP, a TRICK or a GADGET that you would like to share with others, just send it to Ken and he willadd it to our collection.


    Electronic equipment contains dangerous voltages and can be hazardous to unqualified service personnel. Only thosewith adequate training, equipment, facilities and experience should attempt to repair any electronic equipment. Theinformation offered on these pages is intended for electronic repair professionals only. Anyone not qualified or lackingthe equipment, facilities or experience for proper and safe electronic repair should consult with a electronic repairprofessional.

    Test Instruments, Jigs and other GadgetsSpray Can Tube KeeperSync ProblemCom Port TesterTesting Power SuppliesTest JigHomemade CRT RestorerSMPS Test JigAn adapter to operate an Apple monitor from a PC10 amp Power SupplyHigh-Current TransformerG2 Pot BypassPC Repair as a future

    Troubleshooting Techniques, TipsA Universal Convergence TechniqueRepairing LCD'sTesting TV/Stereo/VCR infrared remote controlTesting remote control using ordinary AM radio receiverRemove IC's with tiny PC runs and clearancesRepairing speaker ampsCapacitor AlertReplacing a tyr for cassette playersRepair plastic cracks and rebuild any surfaceInfrared Remote Control TestRepairing VCR'sClearing CRT shortsCapacitor LeakageHow to determine a zener diode's voltageService tip on Philips 9" portable TVQuick CRT TestTroubleshooting a unit that blows fusesHow to quiet noisy transformersHow to clear CRT shortsChecking resistorsLocating the component that is causing the fuse to blowLooking for bad connectionsCircuit Transistor Test

  • Troubleshooting uc3842

    TricksSoldering a flat pack ICReplacing the HOTTemporarily repair a worn down pinch rollerCustom build a VCR beltHK shorts in CRT'sRepairing leaky flybacksDepopulating old circuit boardsRiveted mode switches for VCR'sReplacing EEprom's in RCA'sCleaning capstan shafts and rubber pinch rollersRemoving labels to reuseRemoving labelsSolder wick for FBT and rivitsCleaning capstan spindleCapstan roller refurbishingPlastic repairWhat is DAS and why do I need it?Cleaning tape drivesKeeping track of screwsCleaning Video HeadsScope ESREliminating cockroaches

    Test Instruments, Jigs and other Gadgets

    Keep losing the plastic tubing?This extra wire should help.

    Sync problem - submitted by John Peters.

    If you suspect that a monitor is missing a sync signal resulting in it going into power saving try connecting an external6 volt supply to the crt filament. Turn on the supply first to heat the filament. Then turn the monitor on. You can then seeif you have sync, one color missing etc.

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    Com Port Tester - submitted by Greg Stark

    A simple com port tester for PC's and other DTE/DCE equipment. Verifies port activity, confirms 1488/1489 line driversreceivers are functioning ok. The reason for the led's on pin 2 and 3 is whether your connected to DTE or DCEequipment. Terminal/PC/MODEM/PLC anything. The jumpering satisfies every handshake known to RS232communications.DB25FM connectorPin numberframe ground PIN 1 ---- n/c or attach to shield at one end only, not needed for short runsTxd 2-- 1 kohm ----------- + [) red led, anode to 7 groundRxd 3-- 1 kohm --- + [) green led, anode to 7 groundRts/Cts 4--5 jumper 4 to 5Dsr/Dcd/Dtr 6--8--20 Jumper 6 to 8 to 20Ground 7 -- ground -- solder to anode of ledsI built a couple of these with db25fm and db9fm connectors and attached a 2 foot cable to the leds, heat shrunk it alltogether so I could see what was happening when working on PC's in tight places and other comm devices. This thinghas never let me down when testing any COM port. It tells me everything I need to know about the com ports hardwareor if its a software problem. If I see activity sending to the port, the port is OK.

    Testing Power Supplies - submitted by Corey Ross

    If you are having trouble with a Power Supply blowing fuses and are not sure if you got the problem fixed, here is a tip.Get a lamp socket with 2 extending leads and a light bulb. Solder alligator clips on the leads. Put the clips in place ofthe fuse. Power up the PS and turn on the bulb. If the bulb goes extremely bright on power up, the short is still present.If it goes dim more than likely the Power Supply will start working properly. It may take a few seconds or flicker if thepower supply is a Switching Power Supply. This will save you time and money!

    Test Jig - submitted by Woodie Morris

    For NAP (Magnavox, Sylvania, Philco, Phillips) console TV sets, a spare 25"or 26" table model set whose chassis hasbeen destroyed by lightning, makes a very good test jig. Just remove the customer's chassis along with the front panelcontrol from any console model from the c5 chassis (15 years old) up to the present models and it will operate in thistest jig. The only connection to connect/disconnect are vert yoke, hor yoke, speakers, degauss and dag to crt boardand chassis. Two types of vert yoke connectors are used so test jig should have both vert yoke connector types. Do nottry to operate this test jig with 31" or larger as the yoke mismatch as well as pinc components will cause problems.

    Homemade CRT Restorer - submitted by Bruno De March.

    All CRT restorers, including the most expensive, are based on the same principle appliyng discharges between RGBcathodes and G1 inside the tube to remove from the cathodes microscopical particles deposed on them during theCRT lifetime. Those particles diminish the electron emission, and by removing them the tube may be restored. Thehomemade device pictured here is good enough to do this work and gives a good service to the TV and monitorrepairer in all cases when the tube is not totally unrecoverable (all vacuum electron emitters have a limit). I have testedit with many types of tubes and found it useful except in Samsung and some EMC tubes, in monitors. I guess Samsungtubes are the worst. I have never tested it with Trinitron tubes, but I do not see any reason for not trying it, only that Ihave not yet met any exhausted tube of these. The circuit is very simple, and you can make it recovering old materials.The isolation transformer is not essential, it only provides a means for more security. You can use an old tube socket tomake the connections described in the picture (you must of course disconnect the tube from the rest of the monitorcircuits), then apply the 6 to 9 volts to heat up the filaments for some minutes, then switch off and immediatly push andrelease rapidly several times the pusher switch that applies the 220 AC discharge through the light bulb, while thefilaments are still hot. Do it first to one of the three cathodes, then repeat the whole procedure with the other two. Youwill see that when you apply the discharge, the bulb lights up and a little spark can be seen inside the tube. As thefilaments get cold, the bulb flashes get dimmer as you go pushing the switch. When the light does not light anymore,

  • the discharge cannot be made. Turn on again the filament supply and proceed with another cathode. Caution! Do notpush the discharge switch while the filaments are under voltage, you could damage the cathode. For more security,you can use a double-circuit pusher switch that automatically turns off the filament supply. When the three cathodesare treated this way, test the monitor if it is still dim, repeat the procedure the times necessary, but if you do not see anyimprovement, let it be, the tube is unrecoverable. Note the device described, as you see, is intended for use in thecountries where a 220 v. AC supply is available commonly. In USA and other countries where they have 120 volts (orother), you have to experiment if the procedure is directly applicable this way. I suppose a 120 volts discharge woulddo too.

    SMPS Test Jig - submitted by Ron Reyn

    Here is a little item that I use all the time to test power supplies. Most supplies will not start without a load. I use anautomotive brake light bulb. The bulb has two filaments, one I connect to the 5Volt line (Brake filament) and the otherto the 12 volt line (running light filament). This bulb is connected to a standard connector. I used an extender cable cutthe male end off and soldered the bulb to the Yellow and red wires. Both blacks are attached to the sleeve if the bulb. Ifthe supply is good, both filaments will light up almost the same brilliance. I found it great for debugging supplies.Make sure all the other lines to the computer and hardware are disconnected for this test.

    An adapter to operate an Apple monitor from a PC - submitted by Glenn Wilson. Glen is a member of our emaildiscussion groups.. All subscribers have access to his, as well as over one hundred other technician's comments andexpertise.

    Its connections are:

    IBM 15 pin 3 row to Apple 15 pin 2 rowIBM 3 row Apple 2 row Signal Name--------------------------------------------------1 2 Red Video2 5 Green Video3 9 Blue Video4 nc5 nc6 1 Red Video Return7 6 Green Video Return8 13 Blue Video Return9 nc10 11 & 14 Grounds11 nc12 nc13 3 & 15 3=Composite Sync, 15=H Sync14 12 V Sync15 ncnc 4 Monitor ID #1nc 7 Monitor ID #2nc 10 Monitor ID #3The three monitor IDs tell the Apple / Macvideo controller what frequencies or scan rates to output - but the PC computer doesn't need them.

    10 amp Power Supply - submitted by Ron Reyn

    Had a need for a low voltage power supply today with high current, and since it was after 530 and tommorrow beingSunday, I decided to build one. So I got a few parts that I had laying around and built it. Except for the 15 amptransformer, 50 amp bridge and 40,000 Ufd capacitor, I figure the parts would cost about 3 or 4 bucks. The supply isROCK stable and variable from 3 volts to 18 volts. The supply is over voltage and over current protected as a bonus.See figure below.

  • Power Supply - submitted by Michael Ernst

    Years ago, I built a similar power supply like Ron but needed higher output. It works when using 2N3773 transistorsinstead of 2N3055. The limit is then 40 Volts and lots of Amps.

    High-Current Transformer - submitted by Ken Hull

    For a surprise FREE high current transformer look to your 'junk' microwave ovens. Most shops have some layingaround with bad control boards, not repairable (I have nine of them). Just remove the power transformer, chisel awaythe 1000vac winding and take some #12 romex wire, single and wrap that around the core where the old hv windingwas. Formula= 1 turn per volt. Secure and glue it and you have a transformer capable of MANY amps.

    G2 Pot Bypass - submitted by Luc Degrande. Luc is a member of our email discussion groups.. All subscribers haveaccess to his, as well as over one hundred other technician's comments and expertise.

    To eliminate a possible bad G2 pot (or to repair it), I have been using following little circuit (5 components). It uses thepulses from the HOT to create approximately 1000VDC. Feed this into a pot and then to G2. You only need three wiresfrom this module:1 HOT collector2 GND3 G2The circuit (copied from several monitors) from the Hot collector two 1000V fast diodes (BYV96E or equiv.) in serie, to a10n 2KV cap, then to the top of a 2M HV pot, the bottom of the pot via 1M resistor to ground. The wiper of the potgoes to the G2 input on the neck pcb. If you want to connect directly to G2 on the tube (eliminating the resistor andcap already on the neck) you should add on the wiper a 1M resistor to a 10n 2KV cap (as filter). Of course be VERYcarefull when handling, also take care how you mount it it carries over 1KV!! See figure below.

  • PC Repair has a future!> submitted by Greg Stark

    PC repair has a future!!!! You can play this little mpg file back on any player. I liked it and I think a lot of others on thegroup would too. Download mms.mpg

    Troubleshooting Techniques, Tips

    A Universal Convergence Technique - submitted by Edd Whatley

    When confronted with a Big Screen TV and not having its manual to confirm the locations of and adjustment functionsof the pots nor the presence of I.D.'s silk screened on the board . I utilize the following technique

    Initially make small reference "tics" on the pot shaft and its case on all the affected pots with a micro Sharpiepermanent marker (blue seems to work best). This way you can go back to the starting point(s) if necessary. Next Iutilize a test aid made up from a test lead ~ 2 ft long with a standard size E-Z hook on each end. Cut the lead in halfand solder a momentary contact n.o. spst push button switch to the cut ends. My unit has the mini switch enclosed inthe round plastic shell salvaged from a standard size phone plug (guitar...not telex). This permits all the fingers to gripit and the thumb to "blip" the switch rapidly. Hook up your cross hatch generator to the set and set up a large serviceviewing mirror back far enough so that you can look back to it and get a full panoramic view of the whole TV screen.Take one of the E-Z hooks and affix it to the center wiper pot of the specific pot you are about to evaluate, place theother hook on either of the pots outer terminals. A quick "blip" should reveal the color you're working with and it'sdisplacement should clue you in as to its function e.g. hoz or vert bow, skew, trapez, lin etc. Then you can make asheet for reference until you locate the needed controls that need alignment. Should you not get a pattern displacementyou probably chose the outer pot terminal that already had its wiper element set close to that end , so swap to theother terminal. Not too many sets utilize variable inductors on the board anymore, but when they do, you cansuspicion it's a hoz type of adjustment. If the coil utilizes a ferrite screw core I use a mini pocket screw driver that has asmall magnet on the end of the handle. Placing this in the inductor shell will skew the inductance greatly and you cansurmise its function. BTW this technique is very useful in rf circuits if you will use an allen wrench that just pass thru yourslug, this way you can see the tuning effect on your circuit or identify a coils function without disturbing its initial setting.

    Repairing LCD's - submitted by Jeff Roberts. Jeff is a member of our email discussion groups.. All subscribers have

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    access to his, as well as over one hundred other technician's comments and expertise.

    If the lamp is broken of course - replace it. Otherwise a bad lamp will still light. It just won't be a nice white color. Moreof a reddish orange, only lit on the ends or flickering just like any other fluorescent lamp. You can, of course, try tomeasure the output of the inverter but with the loading effect of the meter/scope and the fact that it's a high freq ACoutput I wouldn't know what to look for. Lamps are only about $10 so that's where I start. Even if it doesn't solve theproblem you can still charge the customer, you just tell them there was no sense putting a new inverter onto an oldlamp so you replaced it while you were "in there". I personally wouldn't want to warrantee a laptop with a new inverterand a used lamp. If it comes back next month with the old lamp burnt out you'll be replacing it for free underwarrantee. The customer doesn't know invertors from lamps so they'll assume because the display went black last timeand the symptom is the same that you'll cover it. Lamps and invertors can both be had from JKL through Digikey. Thebiggest problem with invertors is their physical size and mounting holes. I read the warrantee card on a KDS LCDscreen a few months ago, in fine print down at the bottom it said that the lamps AREN'T covered by the warrantee. Thismeans that if the lamps go out while it's under warrantee the unit goes to an authorized service center and they changethem but they get to bill the customer for the work. This may increase the revenue of those that are authorized becausethey will now get paid for a lot more units by the customer instead of KDS but it's also going to make for a LOT of veryunhappy customers. I currently get $135 Cdn to change the two lamps in an LCD. We always change both, nocheapskate onsies thank you very much. Lamps are about $10US - $15Cdn ea so labor shows $100 which iscomparable to what I used to get for a monitor repair. My advice is to go to the places that sell these and get in touchwith the manager, show/explain to the manager that the lamps aren't covered and that if his customers come in withthis symptom they will be better served by sending them to your shop for faster service. A lot of the big box outlet storestake the returns and send them off to a depot. This could leave the customer without his unit for up to a week andthey'll still get a bill. In the next 5 years a lot of these will be failing, the lamps only last a couple of years if left on allthe time. Although I strongly disagree with the idea that LCDs will replace the monitor any time soon (read in the next10-15 years) I don't let opportunities slip by either.

    Testing TV/Stereo/VCR infrared remote control - submitted by Calvin Smith

    Using a camcorder, look in the viewfinder while the camera is looking at the output of the remote. The camera is verysensitive to infrared and works as a great converter so you can see the pulses of data sent by the remote.

    Testing remote control using ordinary AM radio receiver - submitted by Rhonn

    Use an ordinary AM radio for testing remote control by simply pushing some remote button near the radio and movingthe dial near the 500 Khz. If the remote is working you can hear the tone burst from the remote oscillator.

    Remove IC's with tiny pc runs and clearances

    Plated-thru holes with small clearances are the worst. In these cases I sometimes use a dremel tool with a cutoff wheelto cut the leads free of the chip. The leads can then be individually heated & removed by using just an iron. The holescan be be sucked clean after all the leads have been removed. This is probably a slower process, but it guaranteesthat no foils will be damaged in the procedure. This works well for SMD devices too.

    Repairing speaker amps - submitted by Scott Ross

    I have a '90 Legend LS with the Bose individually amplified speakers. Three of the four speaker amp combinationswere very low volume with some motorboating (low freq. oscillation) in the rear speakers. I replaced all the electrolyticcapacitors (the can-shaped ones) with new ones, as I have heard they leak out their electrolytic fluid over time, causingthe gain to go way down, as well as the motorboating and, in some cases, a whining sound. I used a signal generatorto inject a 1000hz signal into the input, as well as my bench power supply to give it 12vdc. After each cap waschanged, I flicked on the power and verified that the tone was coming out of the speaker. I observed that afterreplacing a few of the smaller caps that the gain greatly increased, and after replacing the larger caps that the

  • motorboating vanished. I also replaced the four output transistors on one amp, in the case of this amplifier, they weren-channel mosfets. The device number on the existing transistors is apparently a proprietary Bose number, so Isubstituted an IRFIZ24N, which seems to work fine. If you're not proficient in soldering, get a friend who is, as it's easyto ruin your amplifier.

    Capacitor Alert - submitted by Bill Stark

    Nicachon Capacitors leaking in 1991 and 1992 TV's Mitsubishi, Zenith, VCR Supplies. One Mitsubishi had 2200mfcaps in supply and ones in computer output-to-video chip for tint color 47mf etc. that caused video noise in picture ona 35 in. Look for black solder on bottom of board, black specked traces on bottom and round brown cicles aroundcaps. Caps are blue and black in color. Just look for Nicachon.

    Replacing a tyre for cassette players - submitted by Russell Burns

    Having a problem finding a suitable tyre for a cassette player? Most times I can get the correct width but not thethickness. You can build up the size of the wheel by applying small strips of adhesive label carefully cut out to fit insidethe rim of the plastic wheel then put in place the replacement tyre. Have restored many cassette players that wouldotherwise been scrapped.

    Repair plastic cracks and rebuild any surface - submitted by Gavin Beverely

    Take SuperGlue / CrazyGlue and apply to surface that needs rebuilding or gluing together. As soon as possible take apinch of baking soda and sprinkle on the Crazyglue. This causes the Superglue to set instantly, approx. half a second,and also builds up the surface. This leaves the Superglue and baking soda as hard as granite -no exaggeration. I havenot yet found anything that can compare to the strength and holding power of this stuff. Very useful around plastic.

    Infrared Remote Control Test - submitted by Michael Eminescu

    I found that the best way to test infrared remote controls from all types of equipment is to place them in front of anyhandheld video camera (VHS or VHS-C or 8mm) and push any button on the remote. You will see a series of rapidpulses in the viewfinder or LCD panel indicating that the remote control is working. Also on remote controls that havemore than one infrared LED you can easily see if an LED is not working. This is also an easy way to test for buttons thatare stuck because of dirt on the remote control. This method could also be extended to test any device that uses aninfrared LED such as infrared barriers. That is because the CCD device used in camcorders is sensitive to infrared. Andeven better, if you have a digital camera with an LCD screen (I am referring to the ones that are used with PC or Maccomputers and are able to store images on floppy disk or PCMCIA card) they can be used as well. As they become lessexpensive and smaller, the advantage is obvious - portability to a customer's site. Try it, have fun and be productive!

    Repairing VCR's - submitted by Steve Wright

    The one thing I have found that causes the most problems in VCR's is the mode switch. They come in all shapes andsizes and are usually very cheap, low-quality items. Do yourself a favor and at least clean and lube the mode switch inevery unit that shows any kind of mechanical wierdness. It just may save you a whole lot of time and effort.

    Clearing CRT Shorts - submitted by Jim Kocmoud. Jim is a member of our email discussion groups.. All subscribershave access to his, as well as over one hundred other technician's comments and expertise.

  • If the CRT is shorted Focus to G2, one technique that we use is to disconnect the G2 wire from the CRT PCB. Then,power up the set, and when the focus voltage backfeeds into the G2 and builds up a potential, it will arc thru the G2circuit protector to ground and Voila, short is gone! If the CRT is shorted HV to Focus, we remove the CRT PCB, andhold a grounded screwdriver about 1/2" away from the focus pin. Again, after power up, the resulting arc usuallyclears the short.

    Capacitor Leakage - submitted by Peter Gottlieb with an addendum by Jeff Roberts

    Editors Note: A series of messages on this topic were posted to AnaTek's ELREPAIR email discussion group. Thepostings of Mr. Gottlieb and Mr. Roberts were so helpful and authoritative that got their permission to post them herefor everyone. Thank you Peter and Jeff.

    I have seen quite a few mentions of capacitor leakage, and some references to the "acid" that leaks out. I would like tocorrect this misconception and explain what I have found out about the construction of electrolytics and the dangers ofleakage.

    As you may remember from physics, to get high capacitance you need either a large surface area or very closespacing of the electrodes. Since large surface areas, even in a jelly-roll type construction like in an electrolytic cap, areimpractical, the solution is to get very close spacing between the plates. If you open up an electrolytic you will find aplain aluminum plate, an "insulator", and an aluminum plate with some sort of coating. This coating is actually theinsulator and is very thin. What seems like the insulator is actually a porous holder for an electrolyte solution.

    The electrolyte used in most electrolytic capacitors is a salt solution in a solvent. This solvent is not water (it wouldfreeze too easily), it is some hydrocarbon (frequently DMF, dimethylformamide). The salts used are proprietary to eachcapacitor manufacturer but are not table salt!! The DMF is itself not corrosive and will evaporate once the capacitorseals are breached or the DMF escapes the can. It is the salts that are so corrosive to the circuit traces, especially indamp or humid environments.

    Now for the problems. A dry salt is not corrosive or conductive, but add moisture and major problems start. Any highimpedance circuits can be shorted out or pulled to the wrong state. Power circuits will corrode, short out, and can evencatch fire (it was a fire investigation where I learned of this "interesting" possibility). If you find a capacitor that hasleaked, you MUST thoroughly clean the residue from the board or you may end up with a call-back. This hashappened when a repair is made when it is dry out and then when the humidity increases the camcorder or whateverno longer works properly.

    I saw a comment that corrosion can occur some distance from the leakage. This is because the solvent can carry thesalts further than you may think. You really need to do a lot of cleaning. A few of the salts are UV visible so if you havea UV lamp handy give it a shot, you might get lucky. If a lot of caps have leaked the unit may be Beyond EconomicalRepair unless you can do a bulk cleaning of the board.

    Jeff Roberts added:

    Just to add to your explanation a good way to bulk clean. We have a particular power supply where the electrolyteleaks out and makes a real mess, not only does it corrode the traces but it can be conductive which makes for "extra"traces and shorts and a whole mess of problems.

  • We remove all of the caps and use a Q-tip and alcohol to start the clean up process, we then repair/replace anydamaged traces and then we put them into the dishwasher and let it wash and rinse them. We don't use the dry cyclebut stop it and just let them dry up overnight or with a hair dryer, then replace the caps and it's done. This worksgreat!!!

    The boards clean up like new and all of the electrolyte is cleaned off so there is no future corrosion or problems.Dishwashing soap is VERY powerful and combined with the high pressure water jets the job it does is great, after all ifit'll clean the lasagna pan - a little chemical spill is nothing. Best of all it's cheap and much faster than trying to handclean a board.

    NOTE: We have an old dishwasher that belongs to the shop. I would not advise that you wash any dishes along withany circuit boards since you may end up with electrolyte on your dishes - YECH!

    The following question was posted by a subscriber:

    If the solvent or DMF has not evaporated, is the electrolyte conductive? I would assume so, as I thought the electrolyteserves to bring the capacitance up by allowing charges to migrate very close to the next layer. Perhaps you couldclarify your description of the construction, as I am confused as to what you are calling the "insulator" and the"coating", and why the electrolyte is used.

    Peter Gottlieb's answer:

    To answer your question, yes, if the solvent has not evaporated the electrolyte is conductive. The "solvent" is no morecomplicated than when table salt is dissolved in water. When wet, it is conductive and corrosive (due in part toplating/electrolysis) but when completely dry the salt becomes an insulator. Of course, salts tend to absorb moisturefrom the humidity in the atmosphere so once you get a salt solution on something there will always be a leakage untilit is cleaned. A good example of how salts absorb moisture is the salt calcium chloride, which is used as sidewalkdeicer.

    If you leave a cup of these granules out in a humid area they will absorb moisture until they all melt together into a wetmass. Dessicant packs are made of this same salt, and you can make dessicant packs by sewing a bunch of this saltinto a fabric bag.

    As for the construction of an electrolytic cap, one aluminum electrode is coated with a thin oxide, and thisnonconducting oxide is the insulator in the capacitor. However, this oxide has a rough surface. To get the other plate ofthe cap mechanically close to this rough surface requires a trick - make the other plate a liquid! Thus, the electrolyte isreally the other plate and the electrolyte is in contact with the bare aluminum plate connected to the other terminal.There is a porous (usually paper) separator between the two plates and this serves two purposes: hold the liquidelectrolyte solution, and keep the two metal plates from touching each other.

    You may ask, why can't the two plates touch each other if one is coated with insulating oxide? The answer is that theycan touch, but vibration or shock (mechanical) or a sharp bit of dirt could break the oxide coating and then the capwould short out.

    So, in short, the oxide coated aluminum plate is one electrode and the insulator, and the electrolyte and bare

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    aluminum plate is the other electrode.

    Regarding cleaning, I had read that Tektronix puts their scopes in a spray booth and uses hot water and mild detergentto clean them when they are sent in for major service. This is followed by a day in a 160 degree F oven. I rememberthat their comment was that the water was least damaging of all cleaning methods.

    I used to wash off PDP-11 computer boards in the sink when they became dust encrusted and this really freakedeveryone out. One of my bosses called DEC to ask if this was OK and was told that this was actually the preferredcleaning method. They still thought I was weird, but that is another story...

    Nowadays, with the concern for the ozone layer, all PC board manufacturing uses water-based fluxes and hot watercleaning. However, there are some components that cannot withstand this and they must be installed after the "wash."Some parts have little plastic seals that are removed after the wash, like DIP switches and piezo buzzers. Before you justwash any old board you have to be able to identify whether any components will be damaged and remove them first.You can sometimes tell by those components not having clean connections, an indication they were installed manuallyafter the PC board wash cycle. Relays will have an epoxy seal if they can handle washing. Do not wash a relay that isnot sealed, you will ruin it.

    How to determine a Zener Diode's voltage - submitted by Richard Thomas. Richard is a member of our emaildiscussion groups.. All subscribers have access to his, as well as over one hundred other technician's comments andexpertise.

    Take the good diode and solder a 1K resistor to one end, then apply about 24V across it with the positive of thevoltage source to the banded end of the diode. Now measure the voltage across the diode only with your meter. Thatwill tell you its zener voltage for replacement. The 1K resistor is necessary to drop the excess voltage i.e. if you apply24V and it is a 10V zener then the resistor will drop the other14V and will limit the current to 14/1000=14Ma. Powerwill be140mW across the diode-more than safe for a 1/4W zener or above.

    Service tip on Philips 9" portable TV - submitted by Rick Hille

    I have serviced several Philips model 09PS10C portable color TV sets, and have discovered what I believe to be amanufacturing or design flaw that can lead to a premature demise of the set. There appeared to be a common threadto the failures in all three sets. On closer examination, the fuse on the line voltage converter module was blown as if anoverload had occured. The main DC fuse on the TV chassis was not blown on two of the sets, but evidence ofovervoltage on several electrolytic cans was visible (tops domed-out to almost bursting) in all. The line-converter mainswitch transistor was blown in all cases. Separating the line-converter module from the set and repairing it, I noticedthat its DC output at no load was up around 35V, and well over 25V under load, which was peculiar since it wasfeeding a common DC point that can be externally powered from 12V. There is a 25V electrolytic on this line, so Iwould guess the DC level should be no more than 16 to 18V if properly designed. Since I have no schematic of theunit, I relied on common sense for this estimation and assumed that more than just the switch transistor was faulty withthe converter. The design is a typical flyback type with a crude regulation loop formed from a negative voltage that setsthe switch bias and controls its duty cycle. The negative voltage is produced by a separate winding on the flybacktransformer, and is rectified, filtered, zener clamped, and tied to the switch base through a bias network. The negativevoltage filter cap (C609) is a rather small size 47uF 16V electrolytic, which I would guess has a relatively high ESR atthe frequency of the switcher (40-50kHz). My theory is that it heats up from the fast, tall spikes coming off theregulation winding and dries out, allowing fairly large current spikes to be driven into the zener. The zener fails, orbecomes leaky or resistive. When this happens, the DC bias drifts up towards ground, which increases the duty cycleand hence the DC output voltage of the converter. With the zener open (as found in one of the sets), the DC output hitover 35V with no load. In this particular set, about 6 or 7 transistors and fusible resistors had to be replaced to get itworking again, since the 35V killed the secondary regulator and was briefly presented to the 10V DC bus on the TVchassis. The fact that the converter is always powered when plugged in allowed the high voltage to develop while theset is turned off. The simple fix here is to replace the cheap, obviously under-speed capacitor on the converter module

  • with a better one, such as a 47uF 63V with a 105C temperature rating. A quick external diagnostic is possible. The DCjack at the back og the set presents the converter output on the spring contact when no plug is present. By CAREFULLYpoking a sharp, slender probe tip to the spring without disengaging it from the bypass contact, the DC output of theconverter can be measured without opening the set up. If you see 25V or more, unplug the set, and replace C609 andthe zener (5.6V) before powering it up again. Note that because I did this without a schematic, the zener voltage was atrial and error affair. The TV-on DC voltage appears to be 15V with 115VAC mains, and around 18V when off.

    Quick CRT Test - submitted by submitted by Johannes Jongbloed

    Years ago I was on the road repairing color tv's and also training would-be television technicians. Firstly I would not becarrying CRT testers, Oscilliscopes etc up 20 flights of stairs to service somebodys TV. I had to make some sort ofdiagnosis without all this. I taught my trainees that in most situations you do not need all this equipment apart fromlooking as if you known what your doing and impressing people. We were at the job to fix it, not to look impressive. Inthe case of a suspect CRT, if the filaments voltage is ok and glowing, the EHT(HV) is ok and there is a couple ofhundred volts on grid two. Then by shorting out momentarily the cathodes of the three guns one by one with yourdummy load mains lamp (all real techs do have one do not they) to deck (earth/ground). The result you should get is avery bright red, green or blue raster with retrace lines momentarily. If you do the picture tube is 99 percent ok. And youshould start looking at drive or major grid one problems. I usually short the collectors momentarily of the RGB outputtransistors via the light globe if the unit uses transistors so as not to accidentally short the wrong pins of the CRT. Trythis tip on a known good monitor (or tv) to see the effect and thus have that extra experience to allow you to judge thecondition of a CRT. I hope this makes sense to those of you out there that do need to learn.

    Troubleshooting a unit that blows fuses - submitted by Clint Hamilton

    Something that may be a little more convenient for some; circuit breakers. I have a set I keep around for consistentlyfuse blowing problems from about 1 amp to about 7 amps. Just reset every time they trip until you correct the problem.Connect to existing fuse base with alligator clips.

    How to quiet noisy transformers - submitted by Jeff Roberts. Jeff is a member of our email discussion groups.. Allsubscribers have access to his, as well as over one hundred other technician's comments and expertise.

    Take a can of shellac or varathane. Solder 3-4" wires onto the four corner pins of the transformer so you can hold it bythe wires. Holding onto the wires so that the transformer is inverted and level lower it into a can of shellac or varathaneso that it is submerged up to the pins but do not get the pins wet. Remove and hang to dry for a day or so. This hasquieted quite a few noisy coils and transformers.

    How to clear CRT Shorts - submitted by Mike Fischer

    Remove the CRT card from ther CRT. Ground the G2 pin with jumper clips. Connect the focus pin to a screwdrivershaft. Apply power momentarily to get the HV up. Unplug the power and quickly touch the screwdriver to the CRTanode. Discharging the HV from Focus to G2 often removes internal shorts.

    Checking resistors - submitted by Greg Stark

    I can check 10 resistors on a monitor pcb in just under 2 minutes whereas pulling a leg out method and getting it backin the hole, remembering to soldering them all as I have missed a few in the past takes me almost a 1/2 hr. Now whatI do is cut one of the leads/legs of the resistor about 1/2 way between the resistor body and the point it enters throughthe PCB. Measure it, join it back up and drop a bead of solder at the cut. Its very fast and I can now tell which resistorsI have tested. Never had a problem with the 3 watt and larger resistors separating from excess heat at the solder jointeither. I figured if the solder does melt at this joint, it would probably be for the better than otherwise burning up

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    something or starting a fire.

    Locating the component that is causing the fuse to blow - submitted by Derek Cook. Derek is a member of our emaildiscussion groups.. All subscribers have access to his, as well as over one hundred other technician's comments andexpertise.

    This is a sure fired way of finding your fault: Set your watt meter to 1.5 amps and 0 volts. Turn up the AC until you startdrawing 1 amp for 25 seconds. Turn off AC feel around for the hottest component and there you have it. These are theeasiest to find. Do not let the AC go higher than 16v.

    Looking for bad connections - submitted by Wade Staggs

    When looking for that elusive bad connection on a circuit board a plain old toothbrush is your best friend. Simply runthe toothbrush over the board till your push the bad connection into working. This works great on cold solder joints.

    Circuit Transistor Tester - submitted by Ron Reyn

    Troubleshooting uc3842 - submitted by Johannes Jongbloed

    When you have a Monitor power supply blown up that uses the old favorite uc3842 chopper driver ic. ie, blown mainsfuse, shorted fet, etc., a quick way to determine if the uc3842 ic has survived without taking it out of circuit is tomeasure pins 5,6 and 7 as if pin 5 was the base of a npn transistor, using an analogue meter on rx1. If it readsforward with negative lead on pin 5 and o/c with positive on pin 5, chances are 99% ic ok. Have found this a usefulcheck and saved replacing uc3842 for no reason many times. (Murphy does play a part 1% of the time.)

  • Tricks of the Trade

    Soldering a flat pack IC - submitted by Rog

    A propane soldering iron that has a hot air attachment works great and puts heat in a small area without effectingsurrounding components. Heat the IC, not the legs. It's not ideal in all cases if you want to reuse the IC. Caps, diodes,resistors and transistors are okay. Clean the pads with desolder wick and apply flux, next align the IC and solder thecorners to keep it in place, affix the pc board at a high angle for each side you want to solder, apply solder at the topleg in large enough quantity to were it wants to run down the legs of the IC ( flux is very important for this to workcorrectly). Follow the ball of solder with your iron down the side of the IC as the solder runs down. Clean up the excesssolder on the last few pins at the bottom. This will leave a factory looking solder job. Repeat this for each side of theIC. It may take a little practice to get the angle just right, but once you figure it out, soldering a flat pack will take notime at all.

    Replacing the HOT - submitted by Hille

    Substituting a HOT is a tricky business as explained in countless repair articles, so use my advice at your own risk. Iprovide this information only as an example of the reasoning process I used to successfully replace the HOT in amonitor that I own. In servicing this 19inch Monitor, I discovered the HOT and its current limiter FET both dead. The FETwas cheap and readily available from a large catalog order distributor, but the HOT turned out to be an expensivehard-to-get 1500V 12Amp non-IDD BJT with no (free) detailed data. Having no schematic, I checked all semis andpassives around the flyback, HOT, and E-W circuits, and found an open power resistor in the HOT base drive circuitwhich I speculated to be the primary cause of the destruction. However, I decided that a low-cost, easily obtainedsubstitute of the HOT would have to be used in case I was wrong. In order to determine the HOT parameters I couldn'tfind, I first determined that the Hdeflection and HV flyback were not separate circuits. With a specified H-scan rate upto 96KHz, the HOT could be subjected to a 10usec cycle, and thus would have to be a newer generation (at the date ofthe monitor's manufacture) BJT with high peak Ic and the faster Tstg / Toff times of around 2usec and 0.1usec,respectively. Filtering for the parameters I learned of the original, I found a sub based on this reasoning in the readilyavailable BU2527AF, a relatively inexpensive high performance non-IDD BJT. As a bonus, the monitor maker hadprovided a second mounting hole to accommodate the slightly different SOT-199 package of the sub (manufacturingoption, no doubt). Replacing the HOT, the FET, and the resistor yielded a working monitor with a steady, bright displaythat doesn't overheat or shut down. I haven't touched the base drive circuit at all, so I'm not sure if this was just dumbluck, or the monitor design has good margins, or perhaps the substitute happens to be a dead-ringer for the original. Ihaven't scoped around the flyback, but the excellent picture and monitor behavior would suggest that I don't waste mytime. The only mod I made was to upgrade the rating of the failed resistor by a factor of 2.

    Temporarily repair a worn down pinch roller - submitted by Gilbert Desmarais

    This tips works fine only if the pinch roller is glossy and/or with pits. If there are radial cracks near the borders, it willnot work properly. Press the pinch roller between two fingers and look if radial cracks become visible. To give a secondlife to the pinch roller of a VCR or a tape deck, use a very fine grain sandpaper of at least 1000, 1500 is better. Takethe pinch roller with your fingers and roll it on the sand paper on a hard leveled flat surface. The movement of rotationon the sandpaper needs to be in the opposite direction of the movement of translation. If it is not done this way, thepinch roller will only roll without any effect. If the pinch roller is locked in the same position, it will be oversanded inone area and not sanded in other areas.

    An alternative way to use the sandpaper is to cut a small piece of it, hold it in one of your hand and pass it over thepinch roller that is held with 2 fingers of the other hand. In all cases, don't overdue it, stop when the glossy appearanceand/or the pits disappeared.

    Another way is to fix the pinch roller to a lathe and pass the sandpaper on it while it is rotating.

    Repair worn carbon rubber contacts - submitted by Gilbert Desmarais

  • 1) On some models, the carbon rubber is thick enough, only the surface has lost his conductive properties. Use a veryfine sandpaper, like 1000 grain, and gently remove the old surface of the carbon rubber to expose the new surface.This tip doesn't work if only the rubber surface coated with carbon. This tip work fine if all the rubber has the carbonmixture incorporated in it.

    2) Salvage an old or cheap calculator keyboard. Cut the carbon rubber contact's tip from one key and place it on theother key, from which the defective rubber contact has been removed. I found that one of the following glue methodsworks fine, depending on the rubber material pure silicone sealant (for bathroom) or 5 min. Epoxy glue, 24h epoxydoesn't work. The glue needs to stay flexible when hardened.. To select the appropriate carbon rubber contact, it is bestto make measurements directly on the exposed surface, with the two tips an ohmmeter to find a similar resistivematerial. This is because some circuits use a current or voltage comparator circuit. So if the resistance is too low or toohigh, the circuit could make false triggering of the corresponding key.

    Custom build a VCR belt - submitted by Gilbert Desmarais

    A way to build a custom belt for VCR, is to use an old bicycle tire tube. It can be cut in circular strips with the desiredwidth. It can also be cut in angle, to obtain a different diameter length. This tip only work for belts that are not timingsensitive, like the loading tape belt, because a lot of circumference imperfections are present.

    HK shorts in CRT's - submitted by Nicolas Cannonne. Nicolas is a member of our email discussion groups.. Allsubscribers have access to his, as well as over one hundred other technician's comments and expertise.

    This is useful when you have a CRT short from any cathode to heater. The aim is to apply an ungrounded voltage toheater pins. First cut all traces that goes to the heater pins on CRT board. Then take a wire, make one (or more) looparound FBT core and apply the 2 ends of the wire at the enter of the schema. This signal is something like AC signalgoing from 10V to +15V at the Horizontal frequency rate. So the diodes avoid any negative voltage, the caps aredoing a nice flat 15VDC and the regulator make the 6.3V required for the heater. The LM317 has to be mounted onheatsink. I have added one more diode in input just to drop 0.7V.The less the input is the less the reg heats. Connect to2 output pins directly to the heater pins on CRT board. First thing to do is to check with your scope the output voltageof the wire looped on FBT, may be youll have to do some additional turns to increase voltage. You can replace the 1Kresistor by a 5K pot to adjust the output voltage. Heater usually draws something like 1A. This has saved 3 TrinitronCRT for me.

  • This works for multisync monitors. 99% of the monitors I have seen are using a DC voltage for filament. Thanks for anyfeedback if it doesnt work for you.

    Repairing leaky flybacks - submitted by David

    Burn hard black plastic material to stop the leaking. You can use silicone, it works too.

    Depopulating old circuit boards - submitted by Jeff Roberts. Jeff is a member of our email discussion groups.. Allsubscribers have access to his, as well as over one hundred other technician's comments and expertise.

    We have a solder pot, it is a ring of stainless steel about 8 inches across welded on top of a base plate of regular iron.Try to picture an 8-inch circle of iron (solid across the diameter) then picture a large ring, also 8 inches across but only1 inch wide that gets placed on top of the solid piece. Weld the ring to the plate around the INSIDE of the ring so itbecomes a reservoir. Buy bar solder from the hardware store, usually used for sheet metal work, about $8.00 Cdn perbar. Place the plate on the burner of a stove, it is about the same size as one of the small burners, and turn the burnerto medium, add a couple of bars and in no time at all you have a pot of molten solder, place any old circuit boardacross the top of this rig and it unsolders all of the components that touch the reservoir at the same time, you merelyplace it down and start pulling parts off with your pliers, you can depopulate a monitor circuit board of all it's valuableparts in about 2-5 minutes once you get the hang of it. You can breakdown/depopulate 20 monitor boards and do thecleanup and preliminary sorting in a 6-hour shift. You won't need to buy parts unless it is something special, like aSony IC or a strange video driver. My transistor bins are all full as are my capacitor bins, thyristor bins, bridge bins,coil bins, and IC bins. I have cross reference books so I can always find a good sub from my own stock.

    CAUTION: Wear heavy clothes, long sleeve shirts, goggles and gloves. If a capacitor falls off a board and lands in thepot and goes unnoticed then a minute or so later it will explode!! And you get solder everywhere (yourself, ceiling,

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    walls floor etc.). So you have to be careful. It also smells bad, because the materiel that the circuit boards are made ofdoes not like to heat up like that, fiberglass boards are OK but pheolic smokes and stinks bad. We have a large fan inthe window to exhaust the smoke and we open other windows and doors to keep the air fresh.

    Riveted mode switches for VCR's - submitted by Roger Lonnkvist

    Replace or toss the machine! Get a jar with a screw-on lid (have had success with a sealable plastic parts bag too).Drop in the mode switch, spray in a cleaner spray that has oil in it (Nu-Trol for one) to just cover the switch and letsoak for 24 hours. Remove from jar and spin with a screwdriver, repeat if necessary, dry and wipe off. To be creative,put a piece of thin foam in the bottom of the jar, drop in the mode switch so that a slot or gear is up, drill a hole in thelid for a screwdriver, cover with fluid. Drill a hole in the lid for a screwdriver, cover with fluid, soak and then insertscrewdriver, push down and spin the shaft under the cleaner fluid. To preserve the fluid for reuse, use a second lid orseal original with tape or a screw with a rubber washer. Can be adapted for other carbon or brass wiper devices.

    Replacing EEPROMs in RCA's - submitted by Paul Worthen

    When replacing the EEPROM in an RCA set, sometimes the horizontal is so far off frequency, it is hard to see theparameter number when going into the service mode. To make the numbers visible, switch to the alt input, ordisconnect the antenna. With no video input, the number will be clear and stable.

    Cleaning capstan shafts and rubber pinch rollers - submitted by Paul Worthen

    Use "Scotch Brite" scouring pads. They are usually available at Home Depot, in the paint department. The pads areplastic, therefore won't damage the cap shaft and have the scouring power of "00" steel wool.

    Removing labels to reuse - submitted by Eric Richards

    When you replace a broken back with a new one from the manufacturer you find that there are no labels such asModel number or serial number. If you freeze the label you will break the glue bond and can take the label off the oldback with no trouble and if you are lucky you can stick the label on to the new back with out applying new glue.

    Removing labels - submitted by Eric Richards

    Use CRC oil to remove old labels. Let it soak in for 15 to 30 minutes and most labels will then easy peal off.

    Solder wick for FBT and rivets - submitted by Eric Richards

    Wrap the braid around the FBT pin and press the solder iron on top to soak up the solder. Works better sometimesthan plain (or heated) solder suckers.

    Cleaning Capstan Spindle - submitted by Eric Richards

    Your Fibre glass pencil used for taking paint off PCB tracks can also be used to clean Iron oxide off VCR capstanspindle, but you may prefer to use brass refill. Saves a lot of time compared to using IPA.

  • Capstan Roller Refurbishing - submitted by Tony

    A great repair for capstan gone shiny or slippery is have the roller on the capstan arm to hold it even with a smallgrinder. Turn on the grinder, switch it off right away and let the roller spin at about a 10 degree angel to freshen up therubber just like new. Quick repair and it lasts if the rubber is not dried up too much.

    Plastic Repair - submitted by Ron Reyn

    I have used this on many occasions to repair plastic parts that would not glue together for strength. This repair makesthe part stronger than the original. The repair material can be a paper clip because it is so easily workable, or a leadcut off a small value capacitor or off a 1/4 watt resistor.

    What is DAS and why do I need it? - submitted by Kurt Hanson. Kurt is a member of our email discussion groups.. Allsubscribers have access to his, as well as over one hundred other technician's comments and expertise.

    As time goes by, more and more monitors are being built with microprocessors or microcontrollers incorporated in thecircuitry. The use of these controllers allows for more user/servicer adjustment options at a lower manufacturing cost.This increases the profit margins of the manufacturers. These processors were once only found in the expensive Sun,Sony, Taxan monitors, used in desk top publishing/CAD businesses. Now they are in virtually every monitor madetoday.

    The modern (post 1994) CRT's are "weaker" and do not last more than a few years, without losing picture quality. (Greyscale or white balance, focus and brightness.) These CRT changes make it necessary to readjust them by using somesort of Digital Alignment System or DAS. Sony DAS is not new. It was first used or designed in the middle to late 80's. Itis a way to change or rewrite data bits into registers that are processed by the controllers, using simple, basic serialcommunication.

    Sony's DAS system is protected from piracy by using a "key" installed on LPT1, or printer port. This "key" must beinstalled for the DAS program to initialize. I have been using the Sony system since 1991. My DAS system was puttogether for almost $10,000. I am Radius, HP, Compaq, Sony, Apple and Digital certified for component level repair...I have worked for a big corporation for a long time now. I certainly couldn't afford that amount on my own.

    I understand that you can get the basic DAS system (software and hardware) for under $1000 now. My system is NOTbasic! I can do DAS adjustments on most all monitors now. Major brands at least. Some are certainly not worth thetime though.

  • Cleaning Tape Drives - submitted by Dave Campbell

    A common mistake in tape deck repair (both audio and video) is to use the fluid supplied with cleaning tapes orcleaning kits (OR alcohol). Most cleaning fluids contain mostly alcohol. Alcohol is BAD for rubber parts. It actuallymakes them get harder. Not only should we be cleaning off tape residue, but we should also be softening the surfaceto better grip the associated idlers, capstans and especially the pinch rollers. Houshold Ammonia works infinitely betterfor all rubber parts. You will find it nicely softens as it cleans. You can even soak parts in it. It will not degrade therubber as many solvent type cleaners can. DO NOT clean the heads or metal parts with it as it IS corrosive. If youreligiously clean the pinch rollers with Ammonia you will see a marked improvement in the performance of all tapedrives and many less machines that eat tapes.

    Keeping track of screws - submitted by Mark Melvin

    The idea is to sort the screws and miscellaneous metal hardware in such a manner that when it comes time toreassemble there is no guess work. Cut a square of cardboard about 6" by 6" or 8" by 8" or 6" by 8" or whatever size isappropriate for the type of electronics you disassemble. Glue six or eight magnets about one or two inches apart to thecardboard. Glue in rows, in columns, or any order. It doesn't matter if you use square, rectangular, or round magnets.Radio Shack carries a good selection. I prefer to use the round ones with hallow centers. Next, take the same numberof "post-it" notes and cut them into strips using the sticky portion of the note. Begin to disassemble the device. Place thefirst set of screws on the first magnet and record their location on the "post-it" note label. Using the adhesive label stickthe label to the cardboard or secure the label with a tack to the cardboard above the magnet holding the screws.Continue to disassemble placing each subassembly's screws on a separate magnet with the attached label. If you runinto a nylon screw/washer place it into the center of one of the round hallow magnets (using the magnet as a cup). Usesmaller magnets for smaller screws and metal hardware; use larger magnets for larger screws and larger metalhardware such as pinch roller arms, etc. The screws and metal pieces are neatly sorted by assembly and secured to themagnets. You can gently pick up the board and move it to a safer location knowing that after one hour or two days ortwo weeks the screws will go back to where they came from. If you plan to move the board place a "post-it" noteidentifying which unit they came from. And remember, some of the devices or subassemblies you work on are sensitiveto external magnetic fields so use common sense in keeping the 'mag-board' a safe distance from them.

    Cleaning Video Heads - submitted by Phil Bader. Phil is a member of our email discussion groups. All subscribers haveaccess to his, as well as over one hundred other technician's comments and expertise.

    If you can visualize a Mr Coffee filter, cut down the side ribs to the round center,about every third rib. Will end uplooking like flower petels,now,cut out the circle at bottom, detatching the petals. Holding a dozen at once, you end upwith many little square wipes and some larger round ones. They are food quality, so no dyes or contaminates, lint free,slightly abrasive,and very cheap!

    Scope ESR - submitted by Michael Mayerhofer

    If you have a scope and a signal generator you can easily build something like an ESR meter. All you need is tworesistors, three BNC jacks and cable. I feed a voltage divider (2.7 KOhm in series with 5.6 Ohm to GND) with a100kHz sinus signal from a signal generator. The scope and the capacitor probe are connected in parallel to the 5.6Ohm. During measurement the cap will be in parallel with the 5.6 Ohm resistor and decrease the output amplitude ofthe voltage divider. Adjust the the signal generator to get maximum amplitude in the 5mV/div range of the scope. I usethree resistors for calibration 1, 3.3 and 10 Ohm. Connect the resistors to the capacitor probe and make points at theside of the screen to mark the decrease of the amplitude. As capacitor probe, use the cables of an old multimeter.Mount the voltage divider and the BNC jacks into a little box which is directly connected to the second input of thescope. When checking for bad caps, just switch on the signal generator, change to the second channel of the scopeand everything is ready. This method does not give you a direct reading of ESR, but you easily can estimate the ESRfrom the amplitude of the displayed sinus. The lower - the better. If you dont have a signal generator, you couldconnect a filter to the calibration output of the scope and use this as a source. The calibration output usually has alower frequency in comparison to 100kHZ where ESR is specified, but nevertheless, it should be suitable to identify abad cap. I started to use this technique when I did not even know that ESR meters were available and I got used to it.All I actually do is press two switches and watch the amplitude on the scope as you watch the needle of your ESRmeter. See picture below.

  • Eliminating Cockroaches - submitted by Steve Hagensicker

    Several years ago, when I was confronted by my first cockroaches, I followed the procedure with the Raid and agarbage bag. When I realized this did not kill them all, I tried something else as I knew I would run into more in thefuture and I do not want them things around my house! The next time I came across cockroaches, dozens and in allsizes, I decided to try the freeze method. As cockroaches seek heat, I figured they are probably delicate where cold isconcerned. I took one large dude and placed him in a sealed Bell jar. Next comes the freezer for a 15 minute test. Hecame out looking dead, but I let him warm up and found he was only dazed. Next time was a half hour. This time hewas very dead! Now that a time had been established, I was confident of a simple cure. As I had a fresh, dead one toexamine, I went to roll him over with my forceps. I noticed his antenna being attracted to the forceps as they have aslight magnetic charge. Hmmmmmmm....... cockroaches like heat. Transformers and power supplies give off heatAND magnetic fields. I have come to the assumption they find electronic components by their magnetic fields. (Just alittle info for you). Anyway, the cure? Plastic garbage bag with the mouth rolled up to the VCR and then taped shut. Inthe freezer for 24 hours!! Never had a live one after that! (It has also never harmed the VCR's).

    submitted by Eric Richards

    Use a can of oil spray like CRC 2-23 or CRC 5-56 used in most TV & VCR workshops.

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