I have a mixing console, where one 6-pin stereo pot is erratic. When I turn it all the way down I sometimes can still hear the left channel at full volume.
The circuit is a regular voltage divider where the wiper is connected to a JRC NJM 4580 op amp inverting circuit with two SMD resistors and one SMD capacitor (reverse enigneered).
The only explanation I have is that the pot sometimes looses its GND connection. I connected it to the GND of the other channel, but this didn't change anything, so the error is not on the PCB.
The pot appears to be an ALPS RK12.
So the disconnection must be in the pot itself.
What I don't understand is the following: I can resolder the pot and the error disappears only temporarily. I can even bend the pin during resoldering and it does not change much. However, sometimes when the error is present, all I have to do is touch one pin of the pot with a screwdriver and the error disappears.
How can that be? There is no way a loose contact inside the pot can be that sensitive, or can it? It appears like the signal the screwdriver introduces makes to error go away. Also I am amazed because broken pots usually have a problem with the wiper. But a broken "bottom end" is kind of rare.
I wish I could imagine how a loose connection of the SMD op amp could cause such behavior. I am ready to buy that an SMD circuit responds to screwdriver tapping. I haven't resoldered the op amp yet.
I cannot easily replace the pot, because I need to take the whole device apart which may cause more harm than good. Also the pot is an industrial pot and not easy to get. And worst of all: I'm beginning to doubt that it is really the pot.
Am am aware that answers to my question may be speculative. But I am running out of ideas, so that'll be okay.