[sdiy] OT: Whining Transformer

[harrybissell]

It is very hard to repair switching power supplies unless you have the
schematics, parts
sources, and a good deal of skill (luck)

Probably it is NOT the transformer.  Usually switching power supplies
operate well above the
audio range. Sometimes, because of load problems (too much / too little)
they go into non-continuous
oscillation... and these bursts can produce audio noise.  This WILL be
heard in the transformer
as the core changes with the magnetic fields.

I'd look CAREFULLY at the electrolyic caps first.  If you have a scope
with a true differential probe
(yeah, right... most folks don't... but it is needed to safely look at
line powered switchers...)
you can examine the output from the line capacitor (usually runs at
about 300VDC) and look for
excess ripple, and look at the actual outputs for other signs of
trouble.

I'd consider a new supply if one is available.  If you try and
troubleshoot the supply without a load...
it will not work, or blow up !  If you try and make a load for it... try
getting rid of the possibly hundreds
of watts of heat.   Usually people are just not set up for this type of
repair.  I usually do not bother
myself.

Now if it was a Oberheim Matrix 12 or Expander... I might take the time
:^P

Hi-Pot means nothing to you... it means that it has withstood a very
high voltage from the mains
to ground without breakdown, usually for one minute.

H^) harry

Steve Begin wrote:

> My computer's power supply has started making a high pitched whining
> noise, and I opened it up and tried to isolate the sound and it
> _seems_ to be coming from a transformer, but it's very hard to
> pinpoint the source of the sound, even when holding a cardboard tube
> up to my ear. Is it most likely coming from the transformer?  If so,
> will replacing the transformer help?  If so, do these numbers mean
> anything to anyone? (they were on the transformer but if it's a part
> number I can't seem to find the part anywhere).LT070-3RC
> 0303HI-POT Any advice would be appreciated.  I can't stand high
> pitched whiny noises unless they diguised as music. -Steve