[sdiy] strange PCB faults, was:OTA question

[Harry Bissell]

Electolytic capaciotrs don't usually leak. They dry up and then
pop.  If you didn't see a blown open can, or one that is bulging at'
the top (or ends) its probably not the source.

I'd be more thinking of external fluids (soda pop is a favorite) that
may have spilled inside.

Of course if there is a nickel-cadmium battery then that is an excellent
source of a potentially unfixable leak.  The acid forms all kinds of nasty
intermetallics which are immune to almost everything except mechanical
abrasion (scrape it down to bare metal. This is the famous Korg issue :^)

H^) harry


----- Original Message -----
From: Ingo Debus <igg.debus at t-online.de>
To: synth-diy <synth-diy at dropmix.xs4all.nl>
Sent: Fri, 17 Sep 2010 10:33:32 -0400 (EDT)
Subject: [sdiy] strange PCB faults, was:OTA question


Am 17.09.2010 um 14:51 schrieb Harry Bissell:

> seriously, was it a copper clad perfboard ?  Sometimes there are  
> faults in copper-clad
> where there are subterranian short circuits (contamination in the  
> laminate that can
> join unknown circuit points).

Recently I tried (in vain) to fix a stereo amp, whose PCB in some  
places obviously was soaked with something conductive. The stains  
were visible, and when I placed the test leads of my ohmmeter on the  
PCB it showed a few megohms. Cleaning didn't help much.
Could this come from a leaking electrolytic? Do lytics leak that much?

This amp was oscillating, and I couldn't fix it. Probably unwanted  
feedback paths all over the place.

Ingo
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-- 
Harry Bissell & Nora Abdullah 4eva