Reforming caps and CRTs
hilpert at cs.ubc.ca
Mon Apr 20 23:40:51 CDT 2009
While we're giving electrolytic caps another go-round, here's another angle on
(modern) electrolytic caps:
I was repairing an HP 9815 (desktop programmable calc) a month ago. While
tracing it out to make the schematic, I noticed that a 680 uF, 25V electrolytic
cap for the +15V supply filter had been installed backwards (reversed
polarity). This was not a replacement or earlier repair, it came out of the
factory this way in 1975 (even HP screws up on occasion).
Granted that it's on the output of the regulator so it's not as critical as if
it were the main smoothing cap right after the rectifiers, but it was
nonetheless interesting that the calculator had been running just fine with it
this way since inception (it had nothing to do with the problem I was looking for).
I made note of it in a repair log for the unit, but left it as is. Someday it
night be interesting to take it out to measure it's characteristics.
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