Page 184 - Troubleshooting Analog Circuits

Letters to Bob 171

development, and debugging. Very few people can appreciate the artistic or “seat-of-
the-pants” techniques we apply. I recently supervised somebody in the design of a
circuit pack. It took him a fa0 &ys to do the actual logic design. It took him several
months (on and off) to prepare that design so that somebody could actually build it (a
printed circuit board). He was amazed. He never learned any of that in school. He
still has to get the circuit pack, get parts (a nontrivial task), and debug it. Needless to
say, it’s quite an educational experience for a novice. Even for an experienced de-
signer like me, it’s no trivial task.
This fact is probably responsible for the attitude I have developed over the years: I
expect the worst and am surprised when anything works at all. I am rarely disap-
pointed. I design with this philosophy in mind. (I detect this philosophy in Bob’s
articles, too.)
I run into many people with the opposite frame of mind: They expect the best and
are surprised when it doesn’t work. I have little patience with these people. They are
either geniuses (and I have met two or three of those over the years in this trade), or
they’ve never gone through the design and debugging process. It is truly a humbling
process.
One more comment touched on in Bob’s article: People are continually amazed
when I tell them that I solve most of my problems at my desk with an ohmmeter. That
fact simply points to where half the problems have occurred over the years-in inter-
connections.

John D. Loop
Research Engineer
BellSouth
Atlanta, GA.

Rap’s comment:

I don’t find quite that much use for an ohmmeter, but I agree that there are many
different ways to find a problem. I think I solve about half of my problems by
reading-a schematic, a data book, a customer’s request, a spec sheet, a set of test
results and test conditions. So I guess you could say that half my problems come from
bad connections in the way of communicating.

RAP

Reference
1. Pease, Robert A., “Protection Circuit Cuts Voltage Loss,” Electronic Design, June 14. 1990,
p. 77.