Star Tech Journal

STAR*TECH Journal
September 1987 (11)
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section! If the supply has multiple output
voltages, check those sections also. It is
better to check too many things than not
enough. Once u:p:m a time, a shorted -5
volt regulator cost me a couple more
switching transistors than it should have.
(OK, maybe more than a couple.)
A cornnon problem with the rectifier system
is leaky or dried out capacitors. Even
switch mode power supplies get hot under
heavy loads, and this can cause the filter
caps to dry out. This results in a noisy
output that cah cause problems that seem
to be logic related. The only effective
way to check this is with an O'scope.
Although I have found some supplies will
emit an audible "squeal" during operation
\'.hen the filter caps are going bad.
cnma.
Fortunately, there are very few problems
with the control logic. If you have
checked out "everything" and the supply
refuses to work, you might try looking at
the power supply for the control IC. If it
is OK, look for a resistor that is way out
of tolerance. I have yet to see an IC
failure, not that it doesn't happen. It
just hasn't happened to me, yet.
IN CDD:DSICE
I do believe that should wrap the whole
thing up. Just remerrber -think of cause
and effect, break the supply up into
digestable chunks, and have at it. Sure
you're going to run into the one that just
flat out refuses to return from the dead,
but don't get discouraged. It is the forty
dollar supply that had a ten cent part go
out that makes it all worthwhile .
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