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Yoke buzz

M

mo

Jan 1, 1970
0
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.
 
A

Art

Jan 1, 1970
0
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
 
J

Jerry Greenberg

Jan 1, 1970
0
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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