have seen condition where the cleaning solvent has penetrated the rubber
seal ("bung") of an electrolytic...this causes a chemical breakdown of the
electrolyte -- then the part was sealed with conformal coating and "canned"
-- preserving the degraded part

the condition now is like a small (or large) time bomb.  internal pressure
will eventually cause a catastrophic failure and the breakdown of the
electrolyte produces hydrogen...all it needs is a spark -- as when the unit
has to be replaced...

under the right conditions -- like when you're hanging in your climbing
harness at the top of a telephone pole - this can keep electronics a
exciting profession...or at least require clean underwear...

Ken

-----Original Message-----
From: Peter L. Peres [mailto:plp@ACTCOM.CO.IL]
Sent: Saturday, August 03, 2002 10:37 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: Grease coating + electrolytics = failure


There are types of grease additives, solvents and other organic substances
that cause synthetic plastics and rubbers to fail, including by puffing
up. Until you will know what that grease contained there will be no way to
know if it killed your parts. My suggestion: take a new capacitor of the
same kind, put some grease on it, and seal it in a small box for a few
months (maybe in a warm place). Then inspect it.

There is a REASON for not using just any conformal coating off the shelf
without testing over time. Same for solvents, oil, grease, etc. More
serious firms have people who run these tests and compile lists of
'tested' supplies.

Peter

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