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JVC television - foldover at top of screen

Discussion in 'Electronic Repair' started by Peabody, Jun 6, 2007.

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  1. Peabody

    Peabody Guest

    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.
  2. James Sweet

    James Sweet Guest

    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
  3. 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.
  4. Peabody

    Peabody Guest

    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.
  5. Peabody

    Peabody Guest

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

    Meat Plow Guest


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

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  8. Peabody

    Peabody Guest

    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.
  9. Peabody

    Peabody Guest

    Michael Kennedy says...
    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.
  10. Meat Plow

    Meat Plow Guest

    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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