PWM cooling port no longer working on keypin

Hey there! I noticed my cooling fan stopped working suddenly. I replaced it with a new fan, and it still doesn’t work. I checked out the keypin, and swapped the cooling and the heat fan. It started working just fine. Plugging the heat fan into the PWM port returns no results (I activate cooling fan via Octoprint and have tested it while printing with 100% cooling in the gcode).

Would this be a keypin, motherboard, or firmware issue? Running v4.0.3

Looks like a hardware problem. Very often on those printers, it is a problem on the small interface board behind the printer. If you have a multimeter, you can start with a continuity check.

Thanks so much!

I have posted some time ago a schematic of the board here:

I very much appreciate it, this is amazingly detailed.

I’ve got a similar problem with my part cooling fan. My extruder fan works fine, if I plug the part fan into the extruder connector the fan works. So I tested with my trusty multimeter: extruder fan is getting 24 volts and 65 Milli amps,
The part cooling fan gets 24volts and 6 Milli amps, whether it’s set to 0% or 100%.
Does anyone have any good ideas of what could be wrong?

EDIT: Re-read your comment, Rob. Didn’t see the 6mA. Maybe the MOSFET chip is bad? Leaving my previous comment below in case someone finds it useful.

Since all the fans on the machine have only two wires, speed is controlled with pulses, not volts. A fan set to less than 100% will receive full 24v in quick bursts rather than continuous - a quick on/off/on/off/etc switch. Your multi-meter doesn’t update fast enough to register those millisecond bursts.