Page 182 - Troubleshooting Analog Circuits

Letters to Bob I69

You took many things I learned over my 20 or so years in electronics (and more I
never learned) and trimmed that vast information down into the bare essence. That’s
hard to do. I’ve done both articles and editor work for DECUS (Digital Equipment
Computer Users Society) publications, and I know how much work you put into that
series. Bravo!
I’m probably very lucky. My job involves service, redesign and enhancement of
radiation therapy equipment, computers, etc. The work spans DC to S-band
microwave, analog and digital, picoamps to megawatts. (The hard/fun part is at both
extremes, working with picoamps, or the high-powered circuits, where a not
uncommon component failure mode is “disappearance.”)
I finally evolved my philosophy down to three commandments. (God came up
with 10, but I have enough problems remembering more than one thing at a time. so 3
is enough.)

1. The more tools you can use, the better, but make sure you know how to use those
tools. If you don’t know the operating procedures, capabilities and limitations of your
test equipment, and know what the equipment does to the circuit you are “testing.”
you’re cheating yourself. (The extreme case is microwave. There, just taking the
cover off the circuit can affect it.)

2. Get your blinders off. (Don’t get caught in the analog vs. digital war.) Don’t swear by
your favorite meter or scope, forsaking all others. Instead, realize that no instrument
is the answer to every problem, no generic circuit is best for all occasions. In the
same vein (and plagiarizing an old joke), “Never trust anybody, not even your fa-
vorite meter.” This also goes for just about any written specification.

3. And, finally, you can’t fix it if you don’t understand it. This is the simplest and the
hardest. Even if there is a deadline, take time to study the circuit diagrams, service
manuals, operating guides, and anything else you can find BEFORE you even take
the cover off the box.

Thanks again for a jewel of a job.
Sincerely yours,
Frank R. Borger
Michael Reese/University of Chicago
Center for Radiation Therapy
Chicago, Illinois

Dear Mr. Borger,

You went to the circus and thought about my articles? That’s funny-I am usually
reminded of the Zoo. Boy, when you get into the troubleshooting business, it gets
really strange.
Thank you for your letters. I like your Three Commandments. On your third
Commandment, I wouldn’t quite say “You can’t fix it if you don’t understand it,” but
it does make it a lot harder to fix something if you don’t understand it.

RAP