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RCA D52W20 yokes, got any?

Discussion in 'Electronic Repair' started by Guest, Apr 17, 2007.

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  1. Guest

    Guest Guest

    Hi. got an RCA D52W20 in the shop. Has a bad convergence yoke (blue). This
    yoke is shutting convergence circuit down, revealed from testing. Anyway,
    these seem to be on eternal backorder, so, does anyone have any from a
    scrapped set? RCA sells as a set of 3.

    Thanks in advance, Danny
     
  2. http://www.acme-sales.net/
     
  3. Guest

    Ummm, as hard as it may be to believe, a dead shorted convergence yoke
    should not shut it down. Overheat it yes, but not shut it down.

    That is because the output circuit uses current feedback. In other
    words, short the yoke and you do not pull more current, but it puts
    out less voltage.

    Now if that's what you mean, that the convergence in the channel is
    out, fine. But if it is "shutting down" the whole circuit, look to the
    output circuit for trouble.

    We probably have one. But I need to know if the yokes are
    interchangable before getting rid of one. I know they are specified
    but that's because they are all wired to the same plug for
    convergence. I don't think it is an inherent difference in the yokes.

    However, I have not had convergence windings go bad on a PTV yoke in a
    very long time. I don't even recall ever having one, but I have fixed
    so many I can't be sure. Regular yoke windings yes, but not the
    convergence.

    For the convergence yoke to shutdown the output by overcurrent, the
    only possible scenario would be if BOTH the vertical and horizontal
    windings are shorted to the core/frame, whatever you want to call it.
    That would mess with the feedback. If that actually happened to me I
    would scrutinize that yoke for corrosion, signs of coolant, etc.,
    because it is pretty far fetched. A rare occurance indeed.

    JURB
     
  4. Guest

    Guest Guest

    On further reflection, and trying a borrowed yoke, I am incorrect. Yoke is
    not the problem. I think I was reaching. This has been interesting.....

    Originally, set came in for bad flyback. Put in, worked fine for say ten
    minutes, then conv died. Conv p/s chopper was shorted, but found nothing
    else bad at all. Replaced chopper, seemed to make no difference in the home.
    Well, now I have chassis in shop, so better testing is available.

    Here is what I have discovered -

    1 - conv p/s tries to start 3 times, as it showed 3 quick voltage jumps from
    sec side.

    2 - the 18v p/s start command spikes up 3 times, timed with power supply
    chirp. 12 volts at TP624 is more like 7 volts.

    3 - p/s on command from small signal board spikes 3 times, timed with p/s
    chirp.

    I went over conv board, resoldered and checked with meter all drive
    transistors, resoldered cable connectors on cobv board and p/s. Looked for
    anything odd on ssb and def board, saw nothing odd. Will continue.....mind
    you, sound and unconverged picture work fine.

    Thanks, Danny
     
  5. Jeroni Paul

    Jeroni Paul Guest

    This sounds like the transistor might have come loose from its
    heatsink and it overheated.
     
  6. Guest

    Guest Guest

    Well, original was well mounted to heat sink, and it had shorted. RCA
    replacement (from RCA) reads fine, and I do believe power supply is good.

    Latest thing I have tried is DL032 diode on defl board. Saw a reference to
    it on net, being able to cause this. No help there.
     
  7. Guest

    Guest Guest

    Disregard all. Have service book now, continuing.

    Danny
     
  8. Guest

    Guest Guest

    Fixed. replaced small signal board. solved all the oddball problems.

    Thanks for the assists
     
  9. Guest

    Guest Guest

    Guess I should finish this thread out. Back in mid May, I replaced the small
    signal board and aligned. Problem fixed.

    Danny
     
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