Hi to everyone, since it's the first time I write in this NG

I've little experience in switching PSUs ...
I've one of them (coming from an Amiga 2000) which shuts off at the first
load.
With no load at all, it delivered 5.9V out of 5 nominal.
I reduced it (with the trimmer) to about 5 with no load.
Inserting a little dummy load (47 Ohm) now it doesn't shut anymore, but
with more serios loads (e.g. an HD), it shuts again.
I checked in-circuit capacitors for shorts and ESR increase, tested
diodes and transistors.
It seems an aging problem (the trimmers were still sealed, so no
tampering), but who's bad ?