I am having a bit of a nightmare trying to work out what is happening to the fans on my Mega Pro.

First off, the part cooling fan stopped working, then not long after the extruder fan also stopped working.

I have opened up the printer and when it is on, the LED for both these fans is always on. Putting a multimeter to them reads ~12 V.

If I send a M106 S255 to the part cooling fan, the voltage drops to ~8.5 V.

Tracking the voltage up to the extruder board, it is consistent until the 2 pin connector for FAN0 or FAN2. Both of these return 0 V.

The temperature sensor and heating element are still working as expected though.

I checked what happens on my Chiron (to compare), the fan voltage is 0 until the M106 S255 is set, then the LED comes on and the voltage goes to ~9 V (which is what I expect to happen).

Has anyone got any idea what might be happening? Is the main board gone? Or is it an issue with just the extruder board?

  • $\begingroup$ not sure on that particular printer, but most fans want 5V $\endgroup$
    – Trish
    Jan 19, 2022 at 22:13

1 Answer 1


There is a speed controller or driver connected to the fans via the main circuit board, check that, because voltage drop usually occurs on the driver IC or circuit, disconnect the fans and touch your multimeter probe on the IC pins and pass the M-code.

If you see a voltage drop as before, then the driver has the issue, if the driver gives 12 V or closer voltage then supply direct 12 V to the fans and test them.

if both of them are working, then some supportive component in your mainboard is at fault.


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