[rescue] Sun Kit Needed for EE Student Here

[Wesley Will]

Carl R. Friend wrote:
>    On Thu, 4 May 2006 wa2egp at att.net wrote:
> 
>> But the electrolytics are the ones that go bang. I've never seen
>> a chip capacitor do that (although they may).
> 
>    I have an Indy motherboard that had a surface-mount cap go south

...

>    In any event, I suspect that if I replace it I'll have a good
> spare motherboard.  I just haven't gotten around to it yet....

You may find that the cap went for some reason or other, such as
over-bias because of an upstream failure in something made of
silicone...  Back in high school we had an electronics shop, about
equivalent to the first year of an associates degree program in
reality (if you wanted to actually learn anything about electronics).
 Part of the daily grind was bringing in some sort of junk and
attempting to repair it.  I kept hearing loud bang noises coming from
one bench and wandered over to see what was happening.  Another bang!
 About the time I got over there, mylar and foil everywhere, there
went another electrolytic.

This idiot kid had an old tube shortwave radio receiver, and he had
found a dead electrolytic in the power supply circuit. (1V2 tubes or
similar, IIRC, it has been thirty years, cut me some slack here.)  He
kept plugging new caps in, soldering at first, then after the second
or third one he said he was just using clip-leads.  Power up, BANG!

If idiot-boy had glanced at the rectifier tube, or heaven forbid,
actually plugged it into the tube tester, he might have noticed the
UV-blue glow coming from inside the glass envelope every time he
applied power and just before the cap exploded.  Tube was shot, gassy,
all kinds of weird stuff coming out of there I'm sure, it's a wonder
we didn't all have kids with antlers and fuzzy purple ears.  Replaced
the tube, -then- replaced the electrolytic, and we were listening to
Radio Free somewhere or other a couple minutes later.

In other words, look for WHY the cap cracked, you might not have such
a good spare as you hoped.

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