19 Feb
2004
19 Feb
'04
1:23 p.m.
>>>> "Tony" == Tony Duell
<ard(a)p850ug1.demon.co.uk> writes:
> Now, the questions: what the hell happened?
Failures of tantalums
> (I've witnessed) are usually due to reversed polarity: not only
> are these particular parts long-term residents of the boards, but
> the unregulated +12V supply is the highest DC voltage in the
> machine - how did the - terminal (DC
Tony> FWIW, I've just had tantalum capacitors explode for no good
Tony> reason. In once classic (!) case, I took an IBM CGA card from
Tony> the box of PC bits and plugged it into an expansion slot. One
Tony> of the tants (a decoupling cap on the 5V rail) exploded, but
Tony> the board carried on working, the right image came up on the
Tony> monitor, and the machine passed the POST.
A good way to have your tantalum cap explode is to install it
backwards. That happens occasionally even in products manufactured in
volume -- the robots are not 100% foolproof. It may take a while for
this to happen.
Then again, they also fail due to age, and typically fail shorted. It
turns out there are tantalum caps with built-in fuses. You'd use
these in cases where you don't want to have the downtime resulting
from shorted caps.
paul