Page 165 - Troubleshooting Analog Circuits

I52 12. Roundup of “Floobydust”

Figure 12.4. If you’re worried that some foolish person will ruin a circuit by misadjusting a trimming po-
tentiometer, you can foil the bungler with this “snip-trim’’ network The procedure for trim-
ming V,, to 22 V within I % tolerance is as follows:
If V,, is higher than 23.080 V, snip out R3 (if not. don’t);
then if V,, is higher than 22.470 V, snip out fL, (if not. don’t);
then if V,, is higher than 22. I60 V, snip out Rs (if not. don’t).
Obviously, you can adapt this scheme to almost any output voltage. Choosing the break-
points and resistor values is only a little bit tricky.

1w 1ov

Figure 12.5. One of my pet peeves: an excessive trimming-potentiometer adjustment range (a). The circuit
in (b) suits TTL much better.

The need for good communications is critical-good oral and written communica-
tions, to prevent confusion or false assumptions. After all, it’s not realistic to expect
the system design and every one of its definitions to start out perfect from the first
day. The chief troubleshooter for the system should be the Program Manager, or
whatever he is called. He’ll have his computers, Pert charts, GANTT charts, and so
forth, but, most valuable, he has his people who must be alert for the signs of trouble.