Page 17 - Troubleshooting Analog Circuits

4 I. First Things First

for solving tricky problems, for finding clues, and for deducing what is causing the
trouble. Friends like these can be more valuable than gold.
At National Semiconductor, we usually submit a newly designed circuit layout to a
review by our peers. I invite everybody to try to win a Beverage of Their Choice by
catching a real mistake in my circuit. What we really call this, is a “Beercheck.” It’s
fun because if I give away a few pitchers of brew, I get some of my dumb mistakes
corrected-mistakes that I myself might not have found until a much-later, more-
painful, and more-expensive stage. Furthermore, we all get some education. And,
you can never predict who will find the little picky errors or the occasional real killer
mistake. All technicians and engineers are invited.

Learn to Recognize Clues
There are four basic questions that you or I should ask when we are brought in to do
troubleshooting on someone else’s project:
Did it ever work right?
What are the symptoms that tell you it’s not working right?
When did it start working badly or stop working?
What other symptoms showed up just before, just after, or at the same time as the
failure?
As you can plainly see, the clues you get from the answers to these questions
might easily solve the problem right away; if not, they may eventually get you out of
the woods. So even if a failure occurs on your own project, you should ask these four

a
I
I

Figure I. I. Peer review is often effective for wringing problems out of designs. Here, the author gets his
comeuppance from colleagues who have spotted a problem because they are not as overly
familiar with his circuit layout as he is. (Photo by Steve Allen.)