18 Jun
2011
18 Jun
'11
1:09 p.m.
All the PSUs that have had components pop on me have
all been capacitors in
the mains filter (except the H7140 in my PDP11 but that was only after I had
been messing with it to try to fix it, so that doesn't count).
Not being an expert in electronics I am not sure of the reason for this. Can
someone explain? Is it the type of capacitor? Is that type of capacitor only
used in mains filters? If not, why have I (so far) not seen other PSU
capacitors blow up?
Not sure how far you're going back but...
Mains filters from the 50's and 60's likely had
paper/wax capacitors in them. At least in the US,
there doesn't seem to have been a special rating
system for these but most cap failures were benign (not
purely luck... even though there was no special rating
they were generally made to be on the robust end.)
"Modern" ones (70's onwards) have specially rated X1,
X2, Y2 capacitors. In small filters these are likely to be
ceramics and in larger ones (especially snubber
networks) they are more likely to be boxed film capacitors.
They all have special fire protection and surge voltage
ratings. They do not necessarily lead "Easy" lives - if
some nearby inductive appliance is putting crap into the
power line, it's the small devices on the same circuit
or nearby branch that may end up eating it.
Tim.