[sdiy] Lifespan of Electrolytics?

[Barry L. Klein]

I just purchased a kit (of course) of an ESR meter that supposedly will find
faulty caps due to their high ESR reading.  Anyone here have experience with
it? 
I'd like to say I have a recent memorymoog aquisition I'm fixing with it but
in reality its a Philips Magnavox 27" TV....

Barry


-----Original Message-----
From: Byron G. Jacquot [mailto:thescum at surfree.com]
Sent: Monday, May 20, 2002 8:02 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Lifespan of Electrolytics?


>    I recently got ahold of a Tapco 4400 reverb for cheap because one
channel
>was dead.  After chasing down a handful of 4136s and systematically
replacing
>each one, I came to find that the actual problem was a bad electrolytic in
the
>signal path.  The circuit board is dated 2/17/77.  I'm guessing that
several
>more of the caps in this board are marginal.  What is the expected lifespan
of
>electrolytics, and what are the effects of old and aging ones?  Is it worth
the
>trouble going through any old gear including synths that are past, say,
about
>twenty years and giving them a electrolytic overhaul?  Anyone have
firsthand
>(or secondhand) testimonials?  Thanks.

I've got a mixing console that's about 15 years old, I've owned it for about
3 of them.  I knew it was old enough that the 'lytics were going to be
questionable, but just how important recapping can be hadn't really hit home
yet.  The first time I tried to do serious work on it (more than just firing
it up for 15 minutes to make sure things were wired right), it started
making this "tik-tik pop tizzz.." kinda noise.  Just loud enough that I
couldn't get any work done.

I pulled out the oscilloscope, to see if I could figure out where the noise
was coming from.  It seemed to be everywhere...every insert point, every
output...

I started unhooking channels, one or two at a time.  When I unhooked a
channel, the noise would disappear for a little while, then come back,
insistent as ever...even with large portions of the thing unhooked, the
noise was still there.  With the thing opened up, I started checking for
some "common sense" things, like power & ground & solidity of the multipin
connectors...

Lo & behold, the positive rail would "dance" in time to the ticking noises,
jumping between 16.75 V and 17 V...at that point, I got out the Digikey
catalog, and ordered a whole slew of Panasonic caps.  I got on with the
recapping I'd anticipated.

The noise is gone now...and I'm sititng here with something like a pound of
used electrolytic caps that were pulled from the board.  One of those caps
is bad, and only shows it when it heats up!

Byron Jacquot
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