8 Oct
1998
8 Oct
'98
12:32 p.m.
John Foust wrote:
You are correct: a blown chip tells you where a problem now resides.
It tells you nothing about where the problem *was* before you
shorted the fuse. It was, after all, a *circuit*, meaning one
thing is connected to the next, and all you discovered is which
component will blow up / heat up / char along the way.
I can recall a PDP-16 that would blow one of the chips apart about once
every couple of months; just enough to be annoying. I finally opened it up
and took out the backplane to examine it. On that particular backplane,
they had bus strips connecting the various voltages to the proper
locations. On the card that was blowing a chip, the -15V bus strip was
almost touching another pin, and apparently did touch occassionally. Slight
movement of the bus strip, and problem solved.