Robert Jarratt wrote:
Good news! It looks like I have managed to get this
working again. I
realised I had not checked the electrolytic capacitors on the main logic
board, ones situated far from the main power output boards. I found one
which had a higher ESR than two other identical ones, although the ESR was
still theoretically OK according to the table on my meter it was at the
limit, so I replaced it and the PSU now appears to work. It really goes to
show, *all* electrolytic capacitors should be checked. Picture showing the
one I replaced here:
http://1drv.ms/1PlfKIV.
Interestingly, I had had a similar failure in another of these PSUs, which I
handed to a friend along with a VAX 4000-300 I gave him, in the hope that
he would be able to fix it. As that PSU was already partially dismantled
from my previous investigations, I asked to borrow it back for the purposes
of doing the reverse engineering. I noticed that the same capacitor on that
PSU also has a higher ESR, but again within range of what should be OK. So,
looks like I might try this as a fix for the second bad PSU too, if he is OK
with me trying that.
Regards
Rob
This Capacitor was bad in my PSU too and I've changed it.
So finally, what was wrong with my idea that you sould simply change all
reachable electrolytic capacitors in that PSU to get it working again?
In my Eyes it really isn't worth the effort of testing each one, change them
all to get that thing working halfways reliable again, it is an really bad
desing anyways...
Regards,
Holm
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