On Sat, 15 Jan 2011 16:16:01 -0000, "Ian Field"
wrote:

A relative donated this, said it was sparking when switched on.

On opening the case I found a group of electrolytics behind the bunch of
output wires had vented.

Does anyone know of a specific component failure that causes the regulation
to go haywire?

There's brown glue on the sub-panel on the primary side, this was a common
cause of problems with CRT monitors.

Any help appreciated.

Thanks.

Vented electrolytics are a likely cause of poor requlation. The caps
didn't vent because the output voltage was too high, they vented
because they were poorly manufactured.

One intelligent approach would be to replace every cap on the
secondary side with name brand low ESR caps of the original voltage
and capacity. Also replace any small (100 µF) caps on the primary
side, as well as any high voltage electrolytics on the primary side
that look in any way suspicious. My preferred capacitor for use in
teh secondary of a SMPS is Panasonic FM or FC series. Rubycon,
Nichicon, United Chemicon also make high quality caps.

Another equally valid approach is to buy a new good quality power
supply. Not only are the cheap power supplies built with crap caps,
the fans are garbage also.

PlainBill