Page 22 - The Art and Science of Analog Circuit Design

Jim Williams

understanding by having to fix it. Unfortunately, Tektronix, Hewlett-
Packard, Fluke, and the rest of that ilk had done their work well; the stuff
didn't break. I offered free repair services to other labs who would bring
me instruments to fix. Not too many takers. People had repair budgets ...
and were unwilling to risk their equipment to my unproven care. Finally,
In desperation, I paid people (in standard MIT currency—Coke and
pizza) to deliberately disable my test equipment so I could fix it. Now,
their only possible risk was indigestion. This offer worked well.
A few of my students became similarly hooked and we engaged in all
forms of contesting. After a while the "breakers" developed an armada of
incredibly arcane diseases to visit on the instruments. The "fixers" coun-
tered with ever more sophisticated analysis capabilities. Various games
took points off for every test connection made to an instrument's innards,
the emphasis being on how close you could get utilizing panel controls
and connectors. Fixing without a schematic was highly regarded, and a
consummately macho test of analytical skill and circuit sense. Still other
1
versions rewarded pure speed of repair, irrespective of method. It really
was great fun. It was also highly efficient, serious education.
The inside of a broken, but well-designed piece of test equipment is an
extraordinarily effective classroom. The age or purpose of the instrument
is a minor concern. Its instructive value derives from several perspectives.
It is always worthwhile to look at how the designer(s) dealt with prob-
lems, utilizing available technology, and within the constraints of cost,
size, power, and other realities. Whether the instrument is three months
or thirty years old has no bearing on the quality of the thinking that went
into it. Good design is independent of technology and basically timeless.
The clever, elegant, and often interdisciplinary approaches found in many
instruments are eye-opening, and frequently directly applicable to your
own design work. More importantly, they force self-examination, hope-
fully preventing rote approaches to problem solving, with their attendant
mediocre results. The specific circuit tricks you see are certainly adapt-
able and useful, but not nearly as valuable as studying the thought
process that produced them.
The fact that the instrument is broken provides a unique opportunity. A
broken instrument (or anything else) is a capsulized mystery, a puzzle
with a definite and very singular "right" answer. The one true reason why
that instrument doesn't work as it was intended to is really there. You are
forced to measure your performance against an absolute, non-negotiable
standard; the thing either works or it doesn't when you're finished.

1, A more recent development is "phone fixing." This team exercise, derived by Len Sherman (the
most adept fixer I know) and the author, places a telephone-equipped person at the bench with
the broken instrument. The partner, somewhere else, has the schematic and a telephone. The two
work together to make the fix. A surprise is that the time-to-fix seems to be less than if both
parties are physically together. This may be due to dilution of ego factors. Both partners simply
must speak and listen with exquisite care to get the thing fixed.