On Fri, 21 May 2021 10:48:32 +0100, T i m wrote:

On Thu, 20 May 2021 08:32:09 -0400, legg wrote:

On Wed, 19 May 2021 21:13:02 +0100, T i m wrote:

On Mon, 17 May 2021 15:43:12 -0700 (PDT), whit3rd
wrote:
snip

I assume the 3 legged device on the LV side is a switching transistor

TNo, that has to be the low-voltage rectifier (if it really IS rated for 20A, it has to
be heatsinked); if it's leaky it would be a quasi-short-circuit, and that will deliver
AC to the capacitors you replaced, which would kill 'em soonish.

That's the likely culprit, probably will need to be desoldered to find the part
number, and will be easy-ish to test. Sometimes there's two diodes, center
pin common, in this form factor.

Update: Whilst waiting for the smaller components to turn up I've de
soldered the two devices on the rear of the board to check the part
numbers and (as you say), the three legged one is a rectifier, a
'30H150C' and I've tested it with my DMM (diode test) and it checks
out ok on that (centre pin to both outsides, both ways round etc). I
hope it's good under load as they don't look as easy to find as the
switcher, a KA1M0800?


Any change in performance with ANY of these part subs?

I'm still waiting for the small caps (might be here today, whilst I
have some stock of caps, I never seem to have the spec I want), and I
intend, assuming this wouldn't risk any other stuff, to replace the
two caps, then opto, voltage reg then switcher in that order (as I
believe that was the order you mentioned the likely cause)?

The idea being that it might be interesting to see what it actually
was?

As an aside, I replaced the 4 x 1000uF, 105, LESR output smoothing
caps with new caps but with the wrong wire spacing (I was jumping
about on eBay and clicked the wrong one) but have some good s/h 1500uF
(16V 105, LESR) caps with the right pin spacing that would fit better.
Would using higher capacity be 'better', given it's soft start etc or
would it negatively influence the L-C of the output and so end up
being 'worse'?

Cheers, T i m

You are, occasionally, reapplying power to check function?

RL