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Yoke buzz

Discussion in 'Electronic Repair' started by mo, Jul 6, 2004.

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  1. mo

    mo Guest

    I have a Siemens 68cm TV using a CUC1825 type chassis.
    The yoke is coated with a brown epoxy and I don't understand why it should sing.
    But it does.The tube does not use rings and I think it was a philips tube.
    When the volume is low,the buzz is very annoying.
    Rough guess puts it at 600Hz.
    Does that make sense?
    If it were to vibrate wouldn't it make a sound at the frame rate?

    Cheers Mo.
     
  2. Art

    Art Guest

    How about the same frequency as the vertical deflection circuit?? Seems to
    be a rather common problem with many deflection yokes, esp when applied to
    larger CRT applications. Changing the yoke normally will not mitigate the
    problem. Sometimes physically "tweaking" the yoke a bit will reduce the
    buzz, other routines that have been implemented, if the yoke is not "bonded"
    to the crt is to physically remove the yoke from the crt neck. Dip the yoke
    into clear shellac and allow to thoroughly air dry for a couple days. Then
    reinstall it and do the necessary adjustments to re-acquire proper purity
    and convergence.
    However, if the yoke is bonded to the tube, the only resolution is to have
    it evaluated by a technician to see if the condition is considered "Normal"
    for that particular set. If so then you have no resolve other than contact
    the manufacturer regarding the problem. If not, and the tube assembly is
    still under warranty, then you may have good luck in having that assembly
    replaced. Hope this info helps a bit Gov. Cheers
     
  3. First make sure that the sound is from the yoke, and not from any of
    the other reactive type components in the scan and power supply
    circuits.

    If it is from the yoke, the buzz you hear is most likely at the field
    rate, if anything. You are most likely hearing harmonics since the
    yoke is driven with a sawtooth like drive. You may also be hearing a
    subharmonic of the line drive that is getting combined in the total
    sound.

    Sometimes a winding or a few of them, may loosen up a little, thus
    start to resonate with the scan drive. The glass structure of the
    tube, can also act as an acoustical resonation surface, and even
    amplify the effect even more.

    If you are very well versed and setup to do convergence and purity
    alignments on TV sets, you can remove the yoke, and soak it in
    transformer laquour for a few hours. Then dry it out in an oven for 24
    hours at 160 Deg F. Then let it sit for 24 hours more at room
    temperature, and install it. You will have to re-do the purity and
    convergence setups.

    Make sure you have the funds and availabily to buy a new yoke if the
    one you tried to fix has failed from being handled. In handling any of
    these components there is always a risk.


    Jerry G.
    ========
     
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