Another Unrelated PSU Question

Peter Coghlan cctalk at
Sat Apr 18 12:23:03 CDT 2020

> 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?

In my experience, the next step after bulging is either leaking and a sticky
mess on whatever is underneath or a big bang and sticky mess everywhere.
I'd get rid of the bulging one even if it seems otherwise good, epecially if
leaving it powered for anything other than very short periods.  It will
probably heat up over time and build more pressure.

The high ESR capacitor can't really be contributing much to smoothing so
I think it needs to be replaced before any further investigating can be done.
With any luck, that might sort out all the issues but even if it doesn't, it
would have to have been eliminated anyway.

Peter Coghlan

> Thanks
> Rob

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