Assuming this is an electronic problem, I would first
test all the
electrolytics on an ESR meter. High-ESR capacitors cause the most odd
faults on SMPUSs...
I'll need to find one...
There have been many projects for these in the UK magazines, I would be
suprised if you couldn't find such a projected Stateside. And a google
search should turn up suppliers of ready-built instruments.
I don't like to waste time with these things. If I see one dodgy
electrolytic, I do the lot (at least of that size/value/voltage).
Gordon.