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High pitch whine from flyback xformer

Discussion in 'Electronic Repair' started by [email protected], May 25, 2006.

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  1. Guest

    Hello;

    After rebuilding the SMPS inside my 32" Zenith Z32X31D the other day
    (lightning killed it); The past couple of days I been noticing a very
    loud ear-piercing high pitch whine coming from the flyback transformer
    and when I apply a small amount of pressure to the side of the flyback
    transformer (using a insulated screwdriver) it stops making the noise,
    then when I let go it starts back up again. So it seems when pressure
    is applied to it; it will shutup. I think heat the expansion of the
    ferrite core; triggers it maybe?

    I sometimes hear this distinct sound when I am in stores around the TV
    section. I noticed it ALWAYS made this noise since the day I bought it,
    usually when the TV is first turned on for a few minutes, then it would
    stop. But it's louder now than ever. Should I replace the capacitors in
    the H.O.T. section also? Thanks for any feedback
     
  2. Dani

    Dani Guest

    It's not usually the flyback, but you MAY have to unsolder it, & press
    it
    down firmly to the pcb while soldering it, or hot glue the ferrite bar
    on it.
    You have to remove the flyback, SMPS, & pincushion transformers, &
    coils, & coat them with hot glue. It may be misleading to find out
    which
    one is causing it, as touching the board, in different locations may
    lead you
    to find the wrong part causing it. Carefully, with the set running...if
    you are
    a Tech, use an insulated, plastic, or wooden stick, & gently touch each
    coil, & transformer, just enough to stop the high pitch ringing. Dani.
     
  3. Art

    Art Guest

    If you are going to remove the LOPT, while it is out run a bit of crazy glue
    around the ferrite cores, from the top and bottom. Also a moderate
    application or RTV wil tend to quiet these resonations. In the old days, a
    wooden shim, be it a toothpick, etc would be run down the edge of the cores
    with just enough pressure to stop them from vibrating.
     
  4. Ray L. Volts

    Ray L. Volts Guest

    The intermittent flyback squeal in my Sony WEGA is driving me nuts, too.
    Just haven't gotten around to opening it up -- banging on the front bottom
    of the case kills the noise for a while (when the set's being nice).
    Sometimes these damned epoxy-encased IFBT's start singing when the potting
    cracks internally (where u naturally cannot get at in order to effect
    repair). Many times you can indeed resolve the squeal with nothing but glue
    and/or solder in the right places, but sometimes there's no choice but to
    replace the flyback.

    A useful tool I 'made' for isolating mechanical intermittents is sort of a
    mini rubber mallet -- it's an audio cassette pinch roller pressed on the end
    of a not-too-rigid nylon coil alignment driver. Simple (and cheap) but
    effective. Gently tapping suspect components with this often zeroes in on
    the source. As others have said, this is potentially misleading if you
    have, for example, bad solder joints on or in close proximity to the device
    being struck. But this tool seems to work pretty well in many cases.
     
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