Tl;dr tested pot and it doesn't show any variation across center pin. Is it reasonable to conclude it is the broken part?
Hey everybody,
so recently a coworker and I were reassembling an expensive piece of lab equipment that involves a pot for speed control of a stepper motor. Everything was working pretty well, but while replacing the button that sits over the pot, someone decided that brute force was the way to attach it and hit the button. The stepper no longer turns. Looking at the board nothing appears different, but I grabbed a multimeter and stuck it on the pot where the center pin showed no variation no matter how it was turned. Is it reasonable to conclude that just the pot broke? What else would a more experienced trouble shooter check before ordering a replacement that costs $80-$120?
Best Answer
You can connect another 10K pot in parallel if you want to test it. Leave the existing one set around the middle and see if the functionality comes back. Take care nothing shorts or you may create much worse problems.
Your main concern when you get the replacement pot is to avoid damaging the board (especially the plated through holes). If you don't have really good rework tools (eg.)
one good approach is to cut the existing pot apart and remove one lead at a time, cleaning the holes up with good solder wick.
That method precludes the desolder and test method you are thinking of following.
Of course even if the board is so mutilated, it's generally possible to hack a replacement on there with fly wires, epoxy and such like, but better avoided.