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flyback transformer sparks

Discussion in 'Electronic Repair' started by mm, Feb 17, 2007.

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  1. mm

    mm Guest

    A while back I asked about this, about a flyback transformer that
    sparked from one point on it to another. And the thread turned to
    whether it was worth fixing.

    But I realize I never did find out why this tv transformer was
    different from others. That's more important to me here than fixing
    the tv, because this is just a hobby for me and I like to understand
    things.

    So in other cases where there was sparking I covered the area with a
    layer of GE silicone sealant, or cement I think they used to call it.

    And then there would be no more sparking. But this time, the spark
    moves somewhere else on the flyback. I did this 5 times and every
    time the spark moved, on this SONY tv. Sometimes it moved to the
    other side of the transformer.

    Does that indicate maybe that the high voltage is even higher than
    normal? Or that the insulation of the flyback is weaker than normal?


    Eventually there was more than a half inch of sealant on some sides,
    and the spark moved to where I can hear it loud, but can't even see
    it. Either there is a layer of air space I accidentally left (I don't
    think so) or it is sparking between the layers without an air space,
    or most likely, I think it is sparking between the transformer and the
    circuit board.
    Thanks.

    If you are inclined to email me
    for some reason, remove NOPSAM :)
     
  2. In a nutshell, the flyback transformer is shot. It's bad, and no amount of
    high-voltage dope will fix it.

    Flyback transformers do fail, sometimes a bit too regularly. They are
    essentially big coils of wire and over time they may start arcing
    internally.

    A flyback's job is to create the high voltages necessary to make the picture
    tube light up. The thick red wire going to the suction cup on the picture
    tube can carry 20,000 volts or more, and that's coming from the flyback.
    But if the high voltage can find an easier way to get out to ground, it will
    do so.

    Air has a "breakdown voltage," meaning that an electrical arc will jump
    through it if the voltage is high enough. Dry air has a lower breakdown
    voltage than moist air; this is one reason why it's so easy to generate
    static electricity just by walking across a carpet on a dry day. Since air
    is mostly nitrogen, you'll see a deep blue spark in this case.

    High-voltage "dope" is a special putty used to prevent electricity from
    arcing to the chassis, but as you've witnessed, it can't always work in all
    cases.

    The only option is to replace the flyback transformer with a new one.
     
  3. Guest

    I've seen them with sparks running all over the surface on all sides,
    its due to breakdown not overvoltage. When using HV gloops you've got
    to be very thorough about getting every trace of carbonised plastic
    off first, else applying gloop is pointless.

    The wire insulation will be shot by now, its beyond help. Sparks turn
    everything to carbon.


    NT
     
  4. Ooops, other way around. :) You get static buildup in dry air because there is
    lower leakage and the charge can build up.

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  5. Jamie

    Jamie Guest

    yeah, i was scratching my head on that one too! :)
     
  6. default

    default Guest

    You could have an environmental problem. Something (dust, vapor, UV
    light, high temperature, high altitude, suspended water droplets,
    etc..) in the atmosphere that is either attracted to the coil and
    causing some ionization and breakdown, or attacking the insulation on
    the coil.

    Or just a faulty coil.

    It is usually better to over react to a corona problem, a little bit
    of carbon tracking from a previous breakdown can cause the next.
     
  7. mm

    mm Guest

    As I said, I don't want to get sidetracked like last time by fixing
    the tv.

    But I appreciate the rest of your reply.

    If you are inclined to email me
    for some reason, remove NOPSAM :)
     
  8. mm

    mm Guest

    Great. Thanks. That's what I wanted to know.
    Everything looked very normal, very uniform, including where the
    sparks were. I guess I should have tried scraping off the top layer,
    but maybe
    It's strange. I've been using it as a monitor temporarily, and once
    it sparked every 10 seconds for 4 or 5 times, but most of the time it
    goes a half hour or hour with no sparks. (It's easy to notice when it
    sparks, and hard to recall when it doesn't.) When I'm done using it
    as a monitor, I'll see how it's going. Maybe if it gets worse, I'll
    take off the silicone and see if I can do a better job putting it on.

    If you are inclined to email me
    for some reason, remove NOPSAM :)
     
  9. mm

    mm Guest

    So, a third possibility. Thanks.
    I've done better in the past. It looks something like the Elephant
    Man's head now. :)

    If you are inclined to email me
    for some reason, remove NOPSAM :)
     
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