Re: Tek 465 repair hints, svc manual? (fix story)


Miroslav Pokorni
 

Electrolytics can make a spectacular and quite dangerous 'exit from the
scene'. Personally, I have seen number of tantalums which failed and not
every time the cap was mounted wrong way. Frequently, there is not enough
pieces left to reconstruct polarity, but often enough tantalum slug remains
in place to verify that cause was nastiness of tantalum rather than backward
mounting.

I have also seen a PC motherboard that caught on fire. Company that I worked
for at the time, was making SIMMs and the particular one had only ceramic
caps, all surface mounted components. The cap shorted, most likely one of
those micro-cracks due to high rate of heating the cap. The subsequent
washing supplied moisture, which was never dried out properly. The product
seating on the shelf for months permitted enough silver migration to build
up to a solid short and when module was plugged in, the short heated up FR4
to point of fire, what transferred to connector body and eventually to
motherboard. Company had to buy new motherboard for customer.

However, the most dangerous electrolytic failure that I heard about was a 16
V 'computer grade' (2" diameter X 3" length), wired backwards and facing
front end of bench. That happened at my first employer, few weeks before I
started work with them. The slug, aluminum foil winding with electrolyte,
flew between heads of two guys who were testing prototype and hit the wall
on the other side of lab. I was shown the 'point of impact', there was a
dent �" deep and that was mortar covered brick wall.

Regards

Miroslav Pokorni

----- Original Message -----
From: "Craig Sawyers" <c.sawyers@tech-enterprise.com>
To: <TekScopes@yahoogroups.com>
Sent: Wednesday, February 19, 2003 12:42 PM
Subject: RE: [TekScopes] Re: Re: Tek 465 repair hints, svc manual? (fix
story)


Never
anything really exciting from a capacitor, however, most of the
unfortunate electrolytic experiences were much more sedate than
usually described.
Well, I had an electrolytic blow up in my face once. The pressure relief
was facing me, and POW! Fortunately I wear spectacles, and that stopped
the
goo going in my eyes. I can't quite remember exactly what abuse that
capacitor had had - I suspect that I was expecting more of it than it was
prepared to give (probably exceeding ripple current rating by an order of
magnitude or some such in a quick-and-dirty lash up).

Craig

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