I've been having some very strange issues over the last day or two, which started with a simple comparator circuit as part of a project.
I noticed one of the inputs dragging the other down, and after messing around with different configurations and measuring currents, I could see around 0.5mA flowing IN to one of the inputs!
Now I checked that the opamp was definitely getting power, and there was no short between the pins on the breadboard.
I've tried 8 different MAX492 dual opamps (from the same tube I might add), and a 5532 I had lying around, and they all seem to exhibit the same behaviour.
Potentiometer going into one input, voltage going into the other. That's it. When changing the pot position, the other input seems to track with it. Putting a reasonable resistance value on the other input to tie it down does help, but the problem is still there.
The only thing I've found that works is my MCP608s, but I've only got two and I'm already using them elsewhere.
So my question here is, are there circumstances where the inputs can accept a significant current? Is it a quirk of these particular parts? Or have I just been real unlucky and these old parts are all dead?
Hopefully someone can enlighten me here, happy to take measurements and try different things if anyone thinks it'll help!
Cheers