Troubleshooting an old CRT

Anselm

Anselm

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So my console system monitor, an approximately 14 year old 32" JVC, has been having problems for the past several years. Until it warms up, the CRT will periodicaly go to a flat line in the center of the monitor. If I tap or smack the monitor, it comes back into view. Once it's warmed up, it runs just fine. I've been dealing with this for years, but after dying to a boss fight because of it, I had enough.

Today I opened it up to take a look. First off, I think it was probably a bad idea to run this thing for 14 years without cleaning it, so I did that first.

Before:
[
IMG_4325.jpg


After:
IMG_4328.jpg


I also played with the focus and color depth while I had it open. Anyways, on to the problem.

When I flex the circuit board upwards, the screen stays in focus without flickering or any other issues. I suspect the weight of the flyback transformer has warped the board over the years. I reflowed all of the solder joints on the flyback transformer. That didn't help. I looked at trying to find a way to brace the board to flex it back up, but the way the TV is designed, it has to screw and slide into grooves a certain way. I couldn't figure out how to accomplish it without destroying the case.

I know this thing either has a bad solder joint, or a cracked run somewhere, but since no matter where I touch the board it affects the problem, I can't isolate it. I'm hoping someone here with ACTUAL CRT troubleshooting knowledge can point me in the right direction to focus my efforts. I am not going to trace every run, and reflow every solder joint. I just want to stop having to warm the damn thing up everytime I use it. Any help would be appreciated .

~Anselm~
 
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N

NEO-GEO man

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What will have done this is heat from being so dirty i reckon, and the reason youre getting a flat line across the screen is youre losing the vertical deflection. Check a few of the caps around the board and make sure they are not leaking, cause this is a serious issue with some sets from the mid 90s, especially the brown Nichicon caps. They are notorious for it in NEC branded CRT projectors.

Youre very game putting your hands near or under the HV transformer while the set is on, especially if the bottom is not insulated against touch. Youll be looking at around 14kV to 20kV there, and it will jump through anything if it sees a good path to earth.

Same goes for the neckboard. Stay clear of it while the set is on.

You need to find out what section is responsible for the vertical deflection, and see what is wrong there. Its got nothing to do with the HV transformer, all this does is steps up the voltage. Id start by removing the deflection yoke plug and cleaning it's connections. Then if look at all the connections near this, on the bottom side of the board to be sure they are soldered properly. From there, id check all the caps in this area to be sure they are within spec, and if they are not or they are leaking, replace them with the same capacity, and the same or slightly higher voltage. They are polarity dependend, so be certain they are installed the right way before you turn on the set, cause they will blow if they are installed backwards, and will also blow if the voltage rating is too low.

Dont tamper with the yoke it's self, or the beam correction rings on the neck of the tube, these control astigmatism and unless its miles out, dont touch it.

Its not a good idea to run the set with the vertical deflection collapsed, it will burn a line into the CRT, which cant be fixed.
 
mastamuzz

mastamuzz

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NEO-GEO man said:
What will have done this is heat from being so dirty i reckon, and the reason youre getting a flat line across the screen is youre losing the vertical deflection. Check a few of the caps around the board and make sure they are not leaking, cause this is a serious issue with some sets from the mid 90s, especially the brown Nichicon caps. They are notorious for it in NEC branded CRT projectors.

Youre very game putting your hands near or under the HV transformer while the set is on, especially if the bottom is not insulated against touch. Youll be looking at around 14kV to 20kV there, and it will jump through anything if it sees a good path to earth.

Same goes for the neckboard. Stay clear of it while the set is on.

You need to find out what section is responsible for the vertical deflection, and see what is wrong there. Its got nothing to do with the HV transformer, all this does is steps up the voltage. Id start by removing the deflection yoke plug and cleaning it's connections. Then if look at all the connections near this, on the bottom side of the board to be sure they are soldered properly. From there, id check all the caps in this area to be sure they are within spec, and if they are not or they are leaking, replace them with the same capacity, and the same or slightly higher voltage. They are polarity dependend, so be certain they are installed the right way before you turn on the set, cause they will blow if they are installed backwards, and will also blow if the voltage rating is too low.

Dont tamper with the yoke it's self, or the beam correction rings on the neck of the tube, these control astigmatism and unless its miles out, dont touch it.

Its not a good idea to run the set with the vertical deflection collapsed, it will burn a line into the CRT, which cant be fixed.
Click to expand...

careful here, careful there, if you breathe you are dead! sometimes is better to buy another set on craigslist! good luck with Indiana Jones TV!
 
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Anselm

Anselm

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Thank you, for two helpful posts and one really good laugh :)

mr aize, I went to that website and it sent me in the right direction. I eventually arrived at this one http://www.ehow.com/how_5423677_repair-flat-lining-television.html

NEO-GEO man, thank you for a lengthy, informative post. Lots of valuable infomation there.

With what I learned over the past day about vertical deflection problems, I took it apart again and isolated my search efforts. I found the IC that controls vertical deflection. A 35V, 100uf capacitor right in front of it seems to be the culprit. When I touch that capacitor I get a greater signal error than anywhere else on the board. This capacitor sits above a plastic framing bar. I pushed that bar back a nudge and sure enough, there's some kind of pinkish corrosion under there.

Wednesday I will make a trip to the local electronics store. I need to buy that capacitor, and a discharging rod for the anode, so I can safely take the circuit card out for repair. Once I safely remove the circuit card, I'll be able to identify the other capacitor values associated with the vertical deflection.

Oh, and here is a more accurate identification of the TV now. JVC AV-27bpm, 27" manufactured in June of 1994.

~Anselm~
 
N

NEO-GEO man

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Good stuff mate, im glad you got it narrowed down, fingers crossed its just that cap that is the issue, cause that will be a really cheap fix.

I remember that NEC direct view TVs had a big problem over here with vertical deflection, and it was a leaking capacitor that did all the damage, it slowly lost its values, which meant a fold up at the bottom, eventually it ate a track, and you lost all vertical deflection. I dont remember the value of that cap though, so im not sure if it would be a very simular issue youre seeing with that JVC, since they are both high end Japan made sets ( the ones sold here are/were ) , it may be the case.

Keep us posted how you go :)
 
Anselm

Anselm

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Purchased the suspected bad capacitor, and supplies to make a discharge line for the high voltage anode. If all goes smoothly I should be able to test my repairs before bedtime.
Click to expand...

FIXED!!!! After I removed the circuit card, I found a bad solder joint on the suspected capacitor, completely free of the pad. I also found 3 more bad solder joints on the vertical deflection IC chip. I inspected the rest of the board, reflowed the IC chip, and replaced the capacitor. I no longer have to beat my TV to make it work. :) Only sad thing...I lived with it like that for like 5-7 years. hehehe.

~Anselm~
 
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N

NEO-GEO man

Fake account, shill troll for Christophe Ratel. Us
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Thats awesome news to hear Anslem, glad to have been able to point you close to the source of your problem!! You shouldve just asked me 5 years ago!! ;)
 
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