has anyone come across a squealing chopper transformer in a p/s
is it caused by shorted output or a problem with the p/s itself?

its in a Panasonic TC-63R50N tv.
the p/s uses an STR51213 power ic which seems ok(not shorted).

Lift up the output a bit and see if the squel goes away,
Unless there's an obvious sign of malfunction, methinks
the transformer is mechanically defective, but electrically
OK.

"BigTom" wrote in message ...
has anyone come across a squealing chopper transformer in a p/s
is it caused by shorted output or a problem with the p/s itself?

its in a Panasonic TC-63R50N tv.
the p/s uses an STR51213 power ic which seems ok(not shorted).

i dont know what you mean by "lift up the output a bit"
do you mean disconnect the output lines?
the p/s is on a separate board so i can unplug the outputs.
ive tried doing one at a time 5v 12v 106v and it does make it a bit
quieter but theres still noise there with nothing plugged in.

aurgathor wrote:
Lift up the output a bit and see if the squel goes away,
Unless there's an obvious sign of malfunction, methinks
the transformer is mechanically defective, but electrically
OK.

"BigTom" wrote in message ...

has anyone come across a squealing chopper transformer in a p/s
is it caused by shorted output or a problem with the p/s itself?

its in a Panasonic TC-63R50N tv.
the p/s uses an STR51213 power ic which seems ok(not shorted).

On Tue, 11 Jan 2005 21:35:55 +1100, BigTom wrote:

i dont know what you mean by "lift up the output a bit"
do you mean disconnect the output lines?
the p/s is on a separate board so i can unplug the outputs.
ive tried doing one at a time 5v 12v 106v and it does make it a bit
quieter but theres still noise there with nothing plugged in.

All who've replied have certainly given accurate advice about the
possible fault.
I've been working on a PS board for a Nakamichi lately, having
replaced all the caps to no avial as well as half the resistors.
I only got rid of the noise problem on it after I isolated the
board.(It was grounded to the chassis/case.)
After that no noise.
Check and see if yours is grounded. If so use plastic(uhmw or some
similar plastic or ceramic) block to un-ground it and see if that
helps.
While it may not fix what's actually wrong it may help with the noise.

aurgathor wrote:
Lift up the output a bit and see if the squel goes away,
Unless there's an obvious sign of malfunction, methinks
the transformer is mechanically defective, but electrically
OK.

"BigTom" wrote in message ...

has anyone come across a squealing chopper transformer in a p/s
is it caused by shorted output or a problem with the p/s itself?

its in a Panasonic TC-63R50N tv.
the p/s uses an STR51213 power ic which seems ok(not shorted).

Sometimes these transformers squeal a little bit. They can he mechanically
resonating. Try to see if putting a bit of pressure on the transformer makes
it more quiet. If so, you may be able to put something under it, to keep it
from resonating, or you may have to change it.

Sometimes if the driver device to the transformer in a switching supply
becomes shorted when it fails, the transformer may go defective due to
having an over-current through it. When this happens, the transformer is
normally damaged where it will no longer work.

--

Jerry G.
======


"BigTom" wrote in message ...
has anyone come across a squealing chopper transformer in a p/s
is it caused by shorted output or a problem with the p/s itself?

its in a Panasonic TC-63R50N tv.
the p/s uses an STR51213 power ic which seems ok(not shorted).

"Jerry G." writes:

Sometimes these transformers squeal a little bit. They can he mechanically
resonating. Try to see if putting a bit of pressure on the transformer makes
it more quiet. If so, you may be able to put something under it, to keep it
from resonating, or you may have to change it.

Sometimes if the driver device to the transformer in a switching supply
becomes shorted when it fails, the transformer may go defective due to
having an over-current through it. When this happens, the transformer is
normally damaged where it will no longer work.

Have you ever actually seen this? Usually, when the chopper transistor fails,
there may be a momentary spike in current but something else will open and
protect the transformer's relatively thick primary.

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"Sam Goldwasser" wrote in message
...
"Jerry G." writes:

Sometimes these transformers squeal a little bit. They can he
mechanically
resonating. Try to see if putting a bit of pressure on the transformer
makes
it more quiet. If so, you may be able to put something under it, to keep
it
from resonating, or you may have to change it.

Sometimes if the driver device to the transformer in a switching supply
becomes shorted when it fails, the transformer may go defective due to
having an over-current through it. When this happens, the transformer is
normally damaged where it will no longer work.

Have you ever actually seen this? Usually, when the chopper transistor
fails,
there may be a momentary spike in current but something else will open and
protect the transformer's relatively thick primary.

Actually, I have seen several in the Sony power supplies with the infamous
2SC4834 transistors and with the MX0841. The windings on the smaller
transformer are very small and I have had to replace three of them when the
PS failed. Whether the transformer failed first or the transistors failed
first is unknown, but two of them were failures that occurred with a.c.
surges.

Leonard

On 11-Jan-2005, BigTom wrote:

has anyone come across a squealing chopper transformer in a p/s
is it caused by shorted output or a problem with the p/s itself?

If it's got a ferrite core and is dismantlable you might be able
to extract the cores, leave any gapping in place, coat the
mating faces with the thinnest film of epoxy adhesive, re-assemble,
clamp and allow to cure. Squeal is often magneto-strictive,
made worse by any unfilled, unclamped, gap in the core.