On Tue, 28 Aug 2007 23:19:41 -0400, "RD"
wrote:

I have an Enlight 350W power supply that has been doing a fine job
for
several years. In fact, it is still doing a good job but has recently
developed a high-pitched whining noise. It is not the cooling fan. I
opened
up the supply, and the noise seems to eminate from a section
containing some
good-sized toroidal transformers. There are a couple of power
transistors on
large heat sinks nearby as well, so I don't know which component is
the
noise source. Anyone have any ideas on how to repair this problem? I
was
thinking of squirting a bunch of high temp silicone all over the
components,
but thought that might not be good because it might cause the
components to
heat up too much. I have a new ps on the way, but would be interested
in
hearing theories on how to fix this one.

RD

Magnetostrictive squealing often occurs in SMPS when either the
windings on a core are not tightly wound or held to the core with a
dampening compound. Also, in a ferrite transformer using E-I or
similar cores, unless the segments are properly fixed or glued
together the interface joints will allow minute movement at the
resonant frequency of the SMPS thus resulting in squeal. The only
solution is to remove the transformer and heat it to soften any
adhesive and then take the core apart, clean the faces and then
re-assemble under pressure using a good quality cyanoacrylate
(superglue).