Pretty cool. I had a little trouble at first. ‘Kept turning the pot anti-clockwise but it didn’t seem to reduce the voltage. Upon following the traces I realized that the potentiometer is set up to attenuate in the clockwise direction (Duh! My mind-lock prevented me from trying that). The pot has a flat spot while the wiper is at the opposite extreme. Looking at the photo, the wiper is at the 3 o’clock position which is about 10 volts. 6 o’clock is about 4.5 volts. But this diversion got me wondering: What’s the failure mode if the wiper gets corroded and goes open circuit? Aha. We can test this ’cause the wiper doesn’t have stops. Crank it to the 9 o’clock position and it runs up on the ceramic and is out-of-circuit. You’ll find it jumps up to full voltage (20 volts). Not my favorite… But there is an easy fix. Just solder in a 120K-ohm resistor between the positive output connection and the potentiometer leg closest to the edge of the card. That will cut the output range in half. Nice!
