On 16/05/2021 10:51, T i m wrote:
On Fri, 14 May 2021 09:39:49 +0100, Clive Arthur
wrote:

On 13/05/2021 16:31, T i m wrote:

snipped

Long short, it looks like the 20A x 12V 'open frame' SMPSU has gone
weak?

snip

I'd check the rectifier bridge. One of the four diodes blown and it
becomes a half-wave rectifier.

I replaced the 4 output caps because of the blown one and sorta as
predicted it doesn't seem to have fixed it.

I can go round all the passive components and check the smaller
transistors but there are a couple of big devices underneath (TO220
but bigger style cases), one 3 pin (FET / Transistor) and a 5 legged
one (SMPSU controller device)?

I can probably check for the 400V or so on the input caps (and any AC
voltage present, suggesting those caps had gone dry?) but there is
little point spending too much time (or money) on components, other
than for the fun of possibly repairing it.

After changing the caps and powering it up with no load, I saw a
'weak' (fluctuating) 12V on the DMM but it wouldn't power up with a 5A
load attached (it crowbarred).

Any thoughts?

Cheers, T i m


There looks to be a preset potentiometer, bottom right, in your photo.
Might be worth noting its current position, rotating it from end to end
of its range a few times, then restoring it to the original position. A
spurt of switch cleaner before the above might help, too.

PA