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JVC television - foldover at top of screen

P

Peabody

Jan 1, 1970
0
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.
 
J

James Sweet

Jan 1, 1970
0
Peabody said:
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.

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.
 
M

Malissa Baldwin

Jan 1, 1970
0
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.

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.
 
P

Peabody

Jan 1, 1970
0
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.

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.
 
P

Peabody

Jan 1, 1970
0
Peabody says...
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.

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.
 
M

Michael Kennedy

Jan 1, 1970
0
Peabody said:
Peabody says...





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.

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

Meat Plow

Jan 1, 1970
0
Subject: Re: JVC television - foldover at top of screen - Success!
From: "Michael Kennedy" <[email protected]>
Newsgroups: sci.electronics.repair
Date: Wed, 6 Jun 2007 20:34:08 -0400

Piggybacking:

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

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COOSN-266-06-25794
 
P

Peabody

Jan 1, 1970
0
Meat Plow says...
You would know if you had an ESR meter. Your primitive
method won't detect crap.

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.
 
P

Peabody

Jan 1, 1970
0
Michael Kennedy says...
Thats amazing, you found the caps you needed at rat
shack! They have so few components these days.

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.
 
M

Meat Plow

Jan 1, 1970
0
Meat Plow says...


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.

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.
 
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