NOTES ON TV REPAIR AND DIAGNOSIS V1.01

• 1) About the Author & Copyright
• 2) Related Information
• 3) General Safety Guidelines:
• 4) Fuse Replaced but TV Clicks with Power-on but no other action:
• 5) 'Interesting' TV Switch Mode Power Supply
• 6) Flameproof Resistors in Switch Mode Power Supplies
• 7) Pincushioning Problems
• 8) Foldover at top of Picture
• 9) Excessive Brightness and/or Washed out Picture
• 10) Color Balance
• 11) Degaussing (demagnetizing) a CRT
• 12) Focus problems
• 13) Focus Drift with Warmup
• 14) Intermittent Jumping or Jittering of Picture or other Random Behavior
• 15) Single Vertical Line
• 16) Single Horizontal Line
• 17) High Pitched Sound or Squeal from TV with no other Symptoms
• 18) Blank Picture, Good Channel Tuning and Sound
• 19) Power-on Clicking but no other Action
• 20) Disappearing Red
• 21) Relays in the Power Circuitry of TVs
• 22) Revival of Dead Remote Control Units
• 23) Loss of Horizontal Sync (also applies to vertical) after Warmup
• 24) Adjustment of the SCREEN Controls
• 25) TV turns off after warming up
• 26) Focus Drifts with Warmup or Age
• 27) Setup Adjustments Lost
• 28) Loss of Channel after Warmup
• 29) About Instant On TVs
• 30) IR Detector Circuit

Author: Samuel M. Goldwasser
E-Mail: sam@stdavids.picker.com
Corrections/suggestions: [Feedback Form] [mailto]
Copyright (c) 1994, 1995
All Rights Reserved

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

1. This notice is included in its entirety at the beginning.
2. There is no charge except to cover the costs of copying.

You may also wish to see a typical SMPS found in a Panasonic VCR for a general "How they do it". You can find it at URL:
http://www.paranoia.com/~filipg/HTML/FAQ/BODY/vcrps.ps (80KB).
It's a Postscript file so deal with it accordingly. You may wish to read the Postscript FAQ **FIRST** if you have no clue on how to proceed. It's at URL:
http://www.cis.ohio-state.edu/hypertext/faq/usenet/postscript-faq/top.html (SUBMENU).
After you read the FAQ, and your questions are still unanswered, you may choose to ask your question on the group: comp.lang.postscript.

• TVs
• Monitors
• Microwave Ovens

Note that the danger to you is not only in your body providing a conducting path, particularly through your heart. Any involuntary muscle contractions caused by a shock, while perhaps harmless in themselves, may cause collateral damage - there are many sharp edges inside this type of equipment as well as other electrically live parts you may contact accidentally.

The purpose of this set of guidelines is not to frighten you but rather to make you aware of the appropriate precautions. Repair of TVs, monitors, microwave ovens, and other consumer and industrial equipment can be both rewarding and economical. Just be sure that it is also safe!

• Don't work alone - in the event of an emergency another person's presence may be essential.
• Always keep one hand in your pocket when anywhere around a powered line-connected or high voltage system.
• Wear rubber bottom shoes or sneakers.
• Don't wear any jewelry or other articles that could accidentally contact circuitry and conduct current, or get caught in moving parts.
• Set up your work area away from possible grounds that you may accidentally contact.
• Know your equipment: TVs and monitors may use parts of the metal chassis as ground return yet the chassis may be electrically live with respect to the earth ground of the AC line. Microwave ovens use the chassis as ground return for the high voltage. In addition, do not assume that the chassis is a suitable ground for your test equipment!
• If circuit boards need to be removed from their mountings, put insulating material between the boards and anything they may short to. Hold them in place with string or electrical tape. Prop them up with insulation sticks - plastic or wood.
• If you need to probe, solder, or otherwise touch circuits with power off, discharge (across) large power supply filter capacitors with a 2 W or greater resistor of 100-500 ohms/V approximate value (e.g., for a 200 V capacitor, use a 20K-100K ohm resistor). Monitor while discharging and/or verify that there is no residual charge with a suitable voltmeter. In a TV or monitor, if you are removing the high voltage connection to the CRT (to replace the flyback transformer for example) first discharge the CRT contact (under the insulating cup at the end of the fat red wire). Use a 1M-10M ohm 1W or greater wattage resistor on the end of an insulating stick or the probe of a high voltage meter. Discharge to the metal frame which is connected to the outside of the CRT.
• For TVs and monitors in particular, there is the additional danger of CRT implosion - take care not to bang the CRT envelope with your tools. An implosion will scatter shards of glass at high velocity in every direction. There are several tons of force attempting to crush the typical CRT. Always wear eye protection.
• Connect/disconnect any test leads with the equipment unpowered and unplugged. Use clip leads or solder temporary wires to reach cramped locations or difficult to access locations.
• If you must probe live, put electrical tape over all but the last 1/16" of the test probes to avoid the possibility of an accidental short which could cause damage to various components. Clip the reference end of the meter or scope to the appropriate ground return so that you need to only probe with one hand.
• Perform as many tests as possible with power off and the equipment unplugged. For example, the semiconductors in the power supply section of a TV or monitor can be tested for short circuits with an ohmmeter.
• Use an isolation transformer if there is any chance of contacting line connected circuits. A Variac(tm) is not an isolation transformer! The use of GFCI (Ground Fault Circuit Interrupter) protected outlet is a good idea but will not protect you from shock from many points in a line connected TV or monitor, or the high voltage side of a microwave oven, for example. A circuit breaker is too slow and insensitive to provide any protection for you or in many cases, your equipment.
• Don't attempt repair work when you are tired. Not only will you be more careless, but your primary diagnostic tool - deductive reasoning - will not be operating at full capacity.
• Finally, never assume anything without checking it out for yourself! Don't take shortcuts!

Since the fuse doesn't blow now (you did replace it with one of the same ratings, right?), you need to check for:

• Other blown fuses - occasionally there are more than one in a TV. Replace with one of exactly the same ratings.
• Open fusable resistors. These sometimes blow at the same time or in place of the fuses. They are usually low values like 2 ohms and are in big rectangular ceramic power resistor cases or smaller blue or gray colored cylindrical power resistors. If any of these are bad, they will need to be replaced with flameproof resistors of the same ratings. Then check:
  • Rectifier diodes, horizontal output transistor, regulator pass or chopper transistor (if present), and main filter capacitor for shorts. An initial test with an ohmmeter can be done while in-circuit. The resistance across each diode and the collector to emitter of the transistors should be relatively high - a few hundred ohms at lest - in at least one direction (in-circuit). If there is a question, unsolder one side of each diode and check - should be in the Megohms or higher in one direction. Removed from the circuit, the collector-emitter resistance should be very high in one direction at least. Depending on the type, the base-emitter resistance may be high in one direction or around 50 ohms. If any reading on a semiconductor device is under 10 ohms - then the device most likely bad. Assuming that you do not have a schematic, you should be able to locate the rectifiers near where the line cord is connected and trace the circuit. The transistors will be either in a TO3 large metal can or a TOP3 plastic package - on heat sinks. The filter capacitor should eventually measure high in one direction (it will take a while to charge from your ohmmeter). It could still be failing at full voltage, however. If you find one bad part, still check everything else as more than one part may fail and just replacing one may cause it to fail again.
  
  
• Assuming everything here checks out, clip a voltmeter set on its 500 V scale or higher across the horizontal output transistor and turn the power on. Warning - never measure this point if the horizontal deflection is operating. it is OK now since the set is dead. If the voltage here is 100-150, then there is a problem in the drive to the horizontal output circuit. If it is low or 0, then there are still problems in the power supply or with the winding on the flyback transformer.
• Other possible problems:
  • bad hybrid voltage regulator
  • bad startup circuit
  • bad relay contacts as mentioned above.
  
  

                          Q1 switching/reg
                             transistor
                   (+)            ---
                ----+-------------| |---------------+-----------|
          ----  |   |             ---               |          _|_
    AC ---|  |--|   = C1           |                |    diode /_\ D2
    in ---|  |------|---|    +-----+------+         |           |
          ----     (-)  |    | Reg. Drive |         C           |
           D1           |    +-----+------+         C choke     +---- gnd
                        |          |                C          _|_
                        |          |                | +135 cap ___ C2
                        |          |                |  I--->    |+
                        |----------+----------------+-----------+---- + 135

Although at first this appears to short out the line supply, when drawn like this it turns out to be a type of flyback regulator:

Q1 is driven by a pulse width modulated signal a the horizontal rate.

Q1 turns on putting 150 V across choke. Current ramps up in choke - more or less linear until saturation which should not occur. This time increases with increasing load.

Q1 turns off. Since current in an inductor cannot change instantly, current continues to flow, now through D2, C2, and +135 load. LCR (R of load, diode) time constant - charges capacitor and powers load.

It would appear to fail and run away under the following circumstances:

1. Inductance is too low and choke cannot store enough energy even at high duty cycle to supply load. Too high a duty cycle and core saturates at which point transistor blows up.
2. Inductance is too high relative to switching frequency so that choke does not have time to discharge (its current) before next current pulse - DC current will just keep increasing until core saturates. This could only really happen if the switching frequency were too high for some reason unless someone changed core material or something like t.
3. Load is too great due to fault elsewhere.

These usually serve as fuses in addition to any other fuses that may be present (and in addition to their function as a resistor, though this isn't always needed). Since your FR has blown, you probably have shorted semiconductors that will need to be replaced as well. I would check all the transistors and diodes in the power supply with an ohmmeter. You may find that the main switch mode transistor has decided to turn into a blob of solder - dead short. Check everything out even if you find one bad part - many components can fail or cause other components to fail if you don't locate them all. Check resistors as well, even if they look ok.

Then, with a load on the output of the power supply use a Variac to bring up the voltage slowly and observe what happens. At 50 VAC or less, the switcher should kick in and produce some output though correct regulation may not occur until 80 VAC or more. The outputs voltages may even be greater than spec'ed with a small load before regulation is correct.

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In particular, this sounds like a pincushion problem - to correct for pincushion, a signal from the vertical deflection that looks something like a rectified sine wave is used to modify width based on vertical position. There is usually a control to adjust the magnitude of this signal and also often, its phase. It would seem that this circuit has ceased to function. If you have the schematics, check them for 'pincushion' adjustments and check signals and voltages. If not, try to find the 'pincushion' magnitude and phase adjustments and look for bad parts or bad connections in in the general area. Even if there are no adjustment pots, there may still be pincushion correction circuitry.

How old is the TV? If it is fairly new - less than 5-7 years - there is a good chance that it uses this type of vertical output.

When good, a typical value would be in the 200-600 VDC at the CRT. The SCREEN (may be called master brightness or background) control should vary this.

Could also be a problem with biasing of the video output transistors. There may individual controls for background brightness on the little board on the neck of the CRT.

However, we are looking for a common problem since all colors are wrong in the same way.

First, check for bad connections/cold solder joints by gently prodding with an insulating stick.

Adjust the sub-brightness controls (may be called color screed, background, or the like) so that the dark areas of the picture are just visible and neutral gray. Adjust the color gain controls until the brightest areas are neutral white.

This should get you close. If something is still shifting after warmup and get some cold-spray or even a little blower and try to locate the component that is drifting. Most likely a transistor or capacitor.

Tape erasers, tape head degaussers, open frame transformers, and the "ass-end" of a weller soldering gun can be used as CRT demagnetizers but it just takes a little longer. (Be careful not to scratch the screen face with anything sharp.) It is imperative to have the CRT running when using these wimpier approaches, so that you can see where there are still impurities. Never release the power switch until you're 4 or 5 feet away from the screen or you'll have to start over.

KEEP DEGAUSSING FIELDS AWAY FROM MAGNETIC MEDIA!!! I never degauss in a room with floppies or back-up tapes. When removing media from a room remember to check desk drawers and manuals for stray floppies, too. Better safe than sorry.

All color CRTs include a built-in degaussing coil wrapped around the perimeter of the CRT face. These are activated each time the CRT is powered up cold by a 3 terminal thermister device. This is why someone in this thread says it will go away "in a few days". Well, It isn't a matter of time; it's the number of cold power ups that causes it. It takes about 15 minutes of the power being off for each cool down cycle. These built-in coils with thermal control are never as effective as external coils. An exception is the type in the better workstation CRTs that include a manual degauss button.

Because of the built-in degaussers I always lecture people not to store magnetic media within 2 feet of a CRT. (Including VCR tapes being next to TV sets). I have never had anyone heed this advice. But on the other hand I've never had proof that data loss has ever occurred. Once again; better safe than sorry.

I also recommend periodic degaussing to keep the convergence and purity nice and crisp. Rotating a CRT quickly can cause subtle magnetization problems because of the earth's magnetic field.

TVs and monitors (as well as microwave ovens) are particularly hazardous since parts are AC line connected - non-isolated and there is the presence of high voltages as well - 25,000+ Volts in the case of color TVs and monitors.

The focus pot is usually located on the flyback transformer or on an auxiliary PCB near by. The focus wire usually comes from the flyback or if the general area or from a terminal on a voltage multiplier module in some cases. It is usually a wire by itself going to the little board on the neck of the CRT.

If a spark gap (a little 2 terminal device with a 1/8" gap in the middle) is arcing with power on, then the resistive divider has shorted inside the flyback, focus board, or HV multiplier - whatever you TV has - and the this unit will need to be replaced.

Using a suitable voltmeter (range at least 10KVDC), you should be able to measure it connected and disconnected. The ground return will be the outside coating of the CRT which may or may not be the same as the metal chassis parts. If the voltage is very low (less than 2K) and the pot has little effect:

When measured right off of the source disconnected from the CRT circuit, then the problem is probably in the focus network in the flyback (or wherever it originates). Sometimes these can be disassembled and cleaned or repaired but usually requires replacement of the entire flyback or voltage multiplier.

When measured with the CRT connected but reasonable with it disconnected, then check for a bad capacitor on the little circuit board. The CRT could also cause this but it is unlikely.

Focus is usually a separate wire running from the flyback or its neighborhood to the PCB on the neck of the CRT. Look for components in this general area. Use 'cold spray' to isolate the one that is drifting. If you have access to a high voltage meter, you should be able to see the voltage change as the monitor warms up - and when you cool the faulty part. If it is in the flyback, then sometimes the part with the adjustments clips off and can be repaired or cleaned. Most often, you will need to replace the flyback as a unit.

The following is not very scientific, but it works: Have you tried whacking the TV when this happened and did it have any effect? If yes, this would be further confirmation of loose connections.

What you need to do is examine the solder connections on the PCBs in the monitor, particularly in the area of the deflection circuits and power supply. Look for hairline cracks between the solder and the component pins - mostly the fat pins of transformers, connectors, and high wattage resistors. Any that are found will need to be reflowed with a medium wattage (like 40W) or temperature controlled soldering iron.

One other possibility is that there is arcing or corona as a result of humid weather. This could trigger the power supply to shut down perhaps with a squeak, but there would probably be additional symptoms including possibly partial loss of brightness or focus before it shut down. You may also hear a sizzling sound accompanied by noise or snow in the picture, static in the sounds, and/or a smell of ozone.

Check for bad solder connections between the main board and the deflection yoke. Could also be a bad horizontal coil in the yoke, linearity coil, etc. There is not that much to go bad based on your symptoms assuming the high voltage and the horizontal deflection use the same flyback. It is almost certainly not an IC or transistor that is bad.

This could be due to:

1. Dirty service switch contacts. There is often a small switch on the located inside on the main board or perhaps accessible from the back. This is used during setup to set the color background levels. When flipped to the 'service' position, it kills vertical deflection and video to the CRT. If the switch somehow changed position or got dirty or corroded contacts, you will have this symptom. Flip the switch back and forth a couple of times. If there is some change, then replace, clean, resolder, or even bypass it as appropriate.

2. Bad connection to deflection yoke or other parts in vertical output circuit. Bad connections are common in TVs and monitors. Check around the pins of large components like transformers, power transistors and resistors, or connectors for hairline cracks in the solder. Reseat internal connectors. Check particularly around the connector to the deflection yoke on the CRT.

3. Bad vertical deflection IC or transistor. You will probably need the service manual for this and the following. However, if the vertical deflection is done with an IC, the ECG Semiconductor Master Substitution guide may have its pinout which may be enough to test it with a scope.

4. Other bad parts in vertical deflection circuit though there are not that many parts that would kill the deflection entirely.

5. Loss of power to vertical deflection circuits. Check for blown fusable resistors/fuses and bad connections.

6. Loss of vertical oscillator or vertical drive signals.

There are several parts inside the TV that can potentially make this noise - the horizontal flyback transformer and to a lesser extent, the deflection yoke would be my first candidates. In addition, transformers or chokes in the switching power supply if this is distinct from the horizontal deflection circuitry.

I don't know about returning a set to a store that doesn't take refunds (I won't even ask about that!) but assuming that this sound level is normal for the particular model here are a couple of suggestions:

You do not want to coat the TV as this may interfere with proper cooling, but the interior of the entertainment center cabinet could be lined with a non-flammable sounds absorbing material, perhaps acoustic ceiling tiles. Hopefully, not a lot of sound energy is coming from the front of the set.

Move the TV out of a corner if that is where it is located - the corner will focus sound energy into the room.

Anything soft like carpeting, drapes, etc. will do a good job of absorbing sound energy in this band.

If you are desperate and want to check the inside of the set:

It is possible to coat the flyback transformer, but this is used mostly when there a loose core or windings and you are getting not only the 15,735 Hz horizontal but also various sub-harmonics of this. This is probably acceptable but may increase the temperature of the flyback.

Using appropriate safety precautions, you can try prodding the various suspect parts (flyback, deflection yoke, other transformers) with an insulated tool such as a dry wooden stick. If the sounds changes, you know what part to go after. Sometimes a replacement flyback will cure the problem unless it is a design flaw. You do not want to replace the yoke as convergence and other adjustments would need to be performed. Other transformers can be replaced.

Does blank picture' means a totally black screen with the brightness and contrast controls having no effect or whether there is no video but there is a raster - light on the screen. The direction in which troubleshooting should proceed differ significantly depending the answer.

Here are some questions:

1. As above, is there any light on the screen at any settings of the brightness and contrast controls, and/or when switching channels. Can you see any raster scanning lines?
2. Can you hear the high pitched (15735 Hz) of the horizontal deflection?
3. Looking in the back of the set, can you see the glow of the CRT filament?
4. Do you get that static on the front of the tube that would indicate that there is high voltage? Any cracking or other normal or abnormal sounds or smells?

Possible causes of no video: problem in video IF, video amplifiers, video output.

When you say 'clicking' do you mean the sound the relay makes when it is turned on normally or just a 'circuitry coming on' sound?

Could be the microcontroller, relay, or its driver.

Could be HV shutdown, or some other system detecting an out of regulation condition.

Could even be a dried up main filter capacitor that produces an out-of- regulation condition until it warms up (now I am really grasping!).

One possible test might be to vary the line voltage and observe its the set's behavior. It may work fine at one extreme (usually low) or the other. Might give clues as to what is wrong.

I have been given an old color TV. The reception is good, but very often, when the contrast and brightness of the TV image is low (e.g. when a night scene is shown), the red color slowly disappears, leaving behind the green and blue image and many red lines. I have tried cleaning the small potentiometers on the PCB attached to the CRT, suspecting that the problem is caused by poor contacts. The funny thing is that when the test picture comes to the screen (I did it late at night, TV station usually show test pictures after closing, and before opening), a beautiful full color image is displayed, and I could not do any tunning. Presumably, the source of the problem is not with the contacts. After reading some DIY books, I guess that my CRT is too old, and the evaporation of the electrode at the electron gun might have deposited on somewhere nearby, and causes immature discharge. This is only my theory, I am happy to listen to whoever has the experience in this area.

"How is a black and white picture?" (Turn down the color control).

If B/W picture is good, then the problem is somewhere back in the chroma decoder circuitry.

Do you have access to test equipment? It would be useful to check the video input to the PCB on the neck of the CRT and signals on that board. If B/W picture is also bad, then you can compare red and green signals to determine where they are becoming different. The red lines in your description sounds like the red video output circuit is drifting and messing up the background level, blanking, screen, or other setting. Could be a capacitor or other component.

What exactly is the purpose of such a relay ... i.e., why doesn't the power switch on the TV just apply power directly instead of through a relay?

The only unknown is the coil voltage. I would guess either somewhere in the 6-12 volt range. You should be able to measure this on the coil terminals in operation. It will be a DC coil.

Well, the relay controls only the 125 VAC which you should treat with respect - it is a lot more dangerous than the 25KV+ on the CRT!

Almost certainly, the relay will have 4 connections - 2 for power and 2 for the coil. If it is not marked then, it should be pretty easy to locate the power connection. One end will go to stuff near the AC line and the other end will go to the rectifier or maybe a fusable resistor or something like that. These will likely be beefier than the coil connections which will go between a transistor and GND or some low voltage, or maybe directly into a big microcontroller chip.

Of course, the best thing would be to get the schematic. Some big public libraries carry the SAM's photofact series for TVs and VCRs. If not, take 10 minutes and trace it. You should be able to get far enough to determine the relay connections.

Once you are sure of the AC connections - measure across them while it is off and also while it is on. While off, you should get 110-125 VAC. While on and working - 0. While on and not working either 110-125 VAC if the relay is not pulling in or 0 if it is and the problem is elsewhere. We can deal with the latter case if needed later on. Note the even if the relay contacts are not working, the problem could still be in the control circuitry not providing the correct coil voltage/current, though not likely.

While it may be expensive and/or difficult to obtain an exact replacement, these are pretty vanilla flavored as relays go. Any good electronics distributor should be able to supply a suitable electrical replacement though you may need to be creative in mounting it.

Test the remote with an IR detector. An IR detector card can be purchased for about $6. Alternatively, build the circuit at the end of this document. If the remote is putting out an IR signal, then the remote or the TV or VCR may have forgotten its settings or the problem may be in the TV or VCR and not the hand unit.

Problems with remote hand units:

• Dead batteries - solution obvious.
• Corroded battery contacts, Wipe off chemical deposits. clean with pencil erase and/or sandpaper or nailfile.

• Broken connections often between battery contacts and circuit board, possibly on the circuit board - resolder.
• Bad resonator or crystal - replace, but diagnosing this without an oscilloscope may be tough.
• Dirt/spills/gunk preventing keys from operating reliably. Disassemble and wash rubber membrane and circuit board with alcohol or soap and water - dry completely.
• Cracked circuit board - can usually be repaired as these are usually single sided with big traces. Scrape off insulating coating and jumper breaks with fine wire and solder.
• Bad LED. If IR tester shows no output, remove LED and power it from a 9V battery in series with a 500 ohm resistor. If still no output, replace with readily available high power IR LED.
• Bad IC - throw it away! This is usually quite unlikely.

Alternatively, you can use the following procedure:

Turn r,g and b screen controls down. Now turn color control fully counterclockwise --off. Now turn up red screen until the screen just shows a red hue. Now turn red gun down until red tint just goes away. Now do the same with the green and blue screen controls. Now adjust the two DRIVE controls for the best black and white picture. That`s all there is to it. I don`t like to work with just a thin "SETUP" line. Cartoons seem to be the best thing to have on while doing the above procedure. You can also use just plain snow (no program) if you prefer. If you can obtain a good b@w pic. when you`re done, the tube is good and the set if most likely functioning properly. Be patient and go slow while watching the large mirror that you are using during this procedure. (LEE)

When it shuts off, do you need to push the power button once or twice to get it back on? Also, does anything else about the picture or sound change as it warms up?

1. If once, then the controller is shutting the TV down either as a result of a (thermally induced) fault in the controller or it sensing some other problem. Monitoring the voltage on the relay coil (assuming these is one) could help determine what is happening.
2. If twice, then the power supply is shutting down. A couple of possibilities here would be low voltage or high voltage regulation error (excessive high voltage is sensed and causes shutdown to prevent dangerous X-ray emission). A partially dried up main filter capacitor could also cause a shutdown but there might be other symptoms like hum bars in the picture just before this happened. Clipping a good capacitor across the suspect (with power off!) would confirm or eliminate this possibility.

Where is the 'sub power' switch and what kind is it?

Which one does the remote's power control?

It could be that the microcontroller is bad in several ways - taking a long time to warm up and not turning power off properly.

When you say it takes 5 minutes for a picture to appear, is there a raster or snow before this? Can you here the horizontal (15735 Hz) deflection before the picture appears? In other words, is the warmup problem strictly related to tuner functions and not power to the video and sound circuits?

If you have a high voltage meter, you can measure the focus voltage to determine if it is being changed by the focus pot and if it is in the ballpark (2KV-8KV typical). Sometimes, the part of the flyback with the focus pot can be snapped off and cleaned or parts replaced but usually you need to replace the whole unit. There may a capacitor or two on the PCB on the neck of the CRT that could have increased leakage as well thus reducing the focus voltage.

HOWEVER, IF YOU DON'T KNOW WHAT YOU DOING YOU COULD GIVE YOURSELF WORSE PROBLEMS.

The SAMS Photofact manual describes this process- you may be able to get Photofacts from a local library, or you can buy them from Radio Shack or MCM. I think, at least on a KV-20EXR10, you hold down the secret button while turning on the set. An on screen menu appears, and the numeric keys make adjustments and select the adjustments to make. I think you use 1/3 and 4/6 or 4/6 and 7/9 to do this. The secret button is a small black recess in the vide jack/ antenna panel. The adjustments you may need to make are vertical linearity and pincushioning. I strongly suggest you get the SAMS manual before you start making changes.

If it's not an adjustment problem you probably have a bad vertical power supply or output (perhaps $150 or less to get repaired???) It's probably not the yoke, from what you describe. Once again, try not to make any unnecessary changes and document every change you make!!! That way you can go back if you do anything wrong (hopefully). I think the SAMS manual also tells you how to restore factory settings. (myer3812@nova.gmi.edu, flint,mi,usa, Rob myers, gmi-emi)

With both no sound and no picture but a raster and static, it is most likely a problem in the tuner, power to the tuner, or its controller (if non-knob type).

If it recovers after being off for a while, then you need to try a cold spray in the tuner/controller to identify the component that is failing. Take appropriate safety precautions while working in there!

If it stays broken, then most likely some component in the tuner, its controller, or its power supply has failed. There is a slight chance that it could be a bad solder connection - I have seen these in the tuner modules of RCAs on several occasions.

Historically, there were 'instant on' TVs which kept a substantial portion of their circuitry live all the time - especially those using vacuum tubes in at least part of the circuitry (other than the CRT). In these, there was a lot more to fail. Those tubes would continue to change their characteristics for many minutes when warming up. Circuits were also much more touchy - remember all that constant tweaking! Thus, it made sense from the users's perspective to eliminate the warmup period and keep those tubes toasty all the time.

In modern solid state TVs, the only component to really need a warmup period is the CRT. All this means is that you have to wait 20 seconds for the picture to appear.

Component values are not critical. Purchase photodiode sensitive to near IR - 750-900 um or salvage from optocoupler or photosensor. Dead computer mice, not the furry kind, usually contain IR sensitive photodiodes. For convenience, use a 9V battery for power. Even a weak one will work fine. Construct so that LED does not illuminate the photodiode!

	+9V ___/ ___
		    +---------+
	 	    |         |
	 	    \         \
	 	    / 3.3K    /  500
	 	    \         \
	 	    /         /
	 	    |       __|__
	 	  __|__     _\_/_  Visible LED
	IR ---->  _/_\_       |
	      PD    |     B |/ C
	 	    +-------|  2N3904
	 	    |       |\ E
	 	    \         |
	 	    / 10K    _|_
	 	    \         -
	 	    /
	 	   _|_
	 	    -