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squished vertical in Sharp 3LS36 color TV

Discussion in 'Electronic Repair' started by Phil Nelson, Nov 10, 2004.

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  1. Phil Nelson

    Phil Nelson Guest

    I need help fixing the squished vertical in my Sharp 3LS36 TV. This is a
    mini color set from 1986. You can view the symptom at:

    http://antiqueradio.org/art/temp/Sharp3LS36Screen.jpg

    A piece of the schematic showing the vertical circuits is at:

    http://antiqueradio.org/art/temp/Sharp3LS36sch1.jpg

    I have replaced C501, C502, and C503. I measure 9.4vdc at pin 14 of the IC,
    as spec'd. At pin 13 next door, however, I measure close to zero, rather
    than the 6.8vdc called for.

    Ideas? This kind of project is a little beyond me. I can fix old tube
    radios, but don't have solid-state expertise or equipment. So any hints
    would be much appreciated.

    Thanks!

    Phil Nelson
     
  2. Jerry G.

    Jerry G. Guest

    Can be C509, 502, 506, 503. These are very likely to give this type of
    fault.

    Use an ESR meter to properly check the caps, or change them.
     
  3. Ken G.

    Ken G. Guest

    You have to be willing to replace capacitors . Read posts on antique
    radio :)
     
  4. This is a fairly straightforward push-pull output, like the audio
    output stage of a cheap radio. Do you have a scope and any sample
    waveforms? I would be suspicious of C509, it is in the return path to
    ground of the vertical yoke.

    H. R.(Bob) Hofmann
     
  5. Phil Nelson

    Phil Nelson Guest

    Can be C509, 502, 506, 503. These are very likely to give this type of
    Forgot to mention that I already changed C509 (as well as 501, 502, 503 as
    mentioned in original post). Haven't tried 506 yet, though.

    Thanks!

    Phil
     
  6. Franc Zabkar

    Franc Zabkar Guest

    I'm betting that C509 has dried out. I'd change C506 as well.

    Vertical size appears to be regulated by sensing the voltage across a
    2 ohm resistor. The current through this resistor is the vertical yoke
    current. Pin 15 of the IC is the feedback pin.


    - Franc Zabkar
     
  7. Phil Nelson

    Phil Nelson Guest

    Replaced C509 and C506. Still no improvement.
    Do you mean the 2 ohm resistor that looks like it's in package (M601) along
    with a 820 ohm resistor ?

    Thanks!

    Phil
     
  8. Phil,
    Unsavory as it sounds, you may have a shorted turn in the
    yoke vertical winding, as process of elimination narrows down the
    possible culprit.
    Bill(oc)
     
  9. Phil Nelson

    Phil Nelson Guest

    Ouch. Dare I ask how a numbskull like me might test for that condition?

    Regards,

    Phil
     
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