18 Apr
2020
18 Apr
'20
1:57 p.m.
On 2020-Apr-18, at 10:03 AM, Rob Jarratt via cctalk wrote:
I have another PSU I have been meaning to look at for
a long time. This one
has fairly high output ripple and some of the voltages do not appear to be
where they should be. I have checked all the capacitors for ESR and they
appear to be OK, with the exception of the two big smoothing capacitors on
the primary side. One of them appears to be slightly bulging, but has
low-ish ESR, the other has a much higher ESR. Is it possible that these
capacitors could be the cause of the out-of-spec outputs?
What frequency is the ripple - mains frequency (50/60Hz) or switching frequency?
If the ripple is at mains frequency then, yes, the problem could be the mains/primary
filtering. (Primary supply drooping far enough across mains cycles that the switcher is
affected and unable to maintain drive.)
Either way, you could scope the primary supply under operation (some load), to see what
the ripple there looks like.