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

A carefully placed, non-conducting rod (a thick wooden stick
will work) gently pressed on the PS's components one at a time
should find the problem. More than likely it's one of the toroids.
Put a small dab of silicone at the base where it meets the board.

"RD" wrote in message m...
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

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).

On Wed, 29 Aug 2007 03:57:37 GMT, Ross Herbert
wrote:



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 (or sub-multiple) 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).

Another procedure that tends to be rather effective, and has been used, is a
coating of clear shellac to the device in question rather than removing and
seperating the cores. We normally would take the offending item, dunk it
into the material, allow to air dry and repeat the process another two or
three times. Reinstalling the item and checking the preformance afterwards.
"Ross Herbert" wrote in message
...
On Wed, 29 Aug 2007 03:57:37 GMT, Ross Herbert
wrote:



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 (or sub-multiple) 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).

In article , "Art" wrote:
Another procedure that tends to be rather effective, and has been used, is a
coating of clear shellac to the device in question rather than removing and
seperating the cores. We normally would take the offending item, dunk it
into the material, allow to air dry and repeat the process another two or
three times. Reinstalling the item and checking the preformance afterwards.
"Ross Herbert" wrote in message
.. .
On Wed, 29 Aug 2007 03:57:37 GMT, Ross Herbert
wrote:




I know I rebuilt a transformer using shellac, but I think there is better
stuff out there. Shellac also absorbs water when just setting around.
It might initially dry quicker than a varnish.

greg