JVC television - foldover at top of screen

I have JVC model AV-27920 television that goes back a few years.

A few months ago, I began having a problem at the top of the screen. It's hard to describe, but it looks like to top part of the image is folded over and displayed upside down. I guess it looks like the the vertical isn't quite making it all the way to the top before the lines start being displayed.

At first this occurred only when the TV was first turned on, affecting the top couple inches. As the set warmed up over 10 minutes or so, this would gradually shrink, and finally all disappear, and everything looked normal. Nothing strange happens at the bottom fo the screen.

Now, the foldover when cold covers more of the screen, and it no longer goes away completely when warm.

I actually have the Sams schematic on this from folder 4080, and I'm hoping that whatever is failing is something I can replace. An electrolytic maybe?

I don't have any test equipment, but am competent to remove, test, and replace things. So perhaps someone can suggest what to look for. I would appreciate any educated suggestions, either in general or with reference to functions I can find on the schematic.

Thanks very much.

Reply to
Peabody
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Electrolytic capacitors around the vertical output IC, they'll be smallish, probably 1-10 uF at about 50V and usually there will be 2 or 3 that need replacing.

Reply to
James Sweet

If you had tried Google before you posted then you would have found out that the TV is broken and you need to buy a new one.

Reply to
Malissa Baldwin

Thanks very much. The vertical output IC is an LA7832, and the only electrolytic I see on the schematic is a 100 uf between pins 3 and 7.

However, looking back a step to the giant 56-pin IC201, a TA1242N "decoder", there are 2.2 uf electrolytics coming off of pins 24 (V Ramp) and 25 (V Sep Filter).

I'll check those out and see where that leads me. Thanks again for the suggestion.

Reply to
Peabody

For those who might see this thread in the future, I wanted to report that I replaced these capacitors, both of which were very near the vertical output IC:

C424 100uF/35V C425 440uF/35V

And now it works. Both of the caps I removed appear to test ok per my primitive analog voltmeter method, so I suppose it's possible both were good and the fix was just a coincidental result of disassembly/reassembly. We'll never know for sure.

And again for the record, this was a JVC model AV-27920.

$2.80, plus gas money to drive to Radio Shack and back. I just love it when things end this way.

Thanks very much for the help.

Reply to
Peabody

Thats amazing, you found the caps you needed at rat shack! They have so few components these days.

Reply to
Michael Kennedy

Piggybacking:

You would know if you had an ESR meter. Your primitive method won't detect crap.

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Reply to
Meat Plow

On the contrary. It does detect crap, but only pure crap. It will detect open and shorted caps, but it will also detect significant differences in capacitance between two caps of the supposed same value, one of which is known to be good. And that has proved very useful on occasion. But you're right - it only reveals these gross problems, nothing on the level of ESR differences.

Reply to
Peabody

Well, if they are gonna carry any caps at all, these two would be included.

And I notice that I have a typo on one of them - 440 should be 470. It should be:

C424 100uF/35V C425 470uF/35V

Yes, they even have these in both radial and axial, and in different voltage ratings. Then all you have to get past is paying $1.29 each for a capacitor. But, you know, for something like this, it makes sense.

Reply to
Peabody

Back in my early years of service (probably where your at now) the hottest VOM meter was a Simpson 260. I've checks a cap or two since then and now own a Tenma ESR meter.

Reply to
Meat Plow

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