21 Apr
2009
21 Apr
'09
1:53 p.m.
----------------------------------------
Date: Mon, 20 Apr 2009 21:40:51 -0700
From: hilpert at cs.ubc.ca
To: General at invalid.domain
Subject: Re: Reforming caps and CRTs
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).
---snip---
The cap is most likely completely dry inside. It would
have cooked completely by now. It is possible to reform a
cap backwards but that requires a slow current for
a long time. Of course, the capacitance would be really
small because the case has a small surface area compared
to the positive terminal.
Dwight
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