no longer able to control fan speed through PWM on d9

Recently had a slight mishap with my custom AC part fan mount, resulting in ripped off wires and a catastrophic short on the d9 MOSFET on my RAMPS 1.4plus. (house fire averted, thankfully) O_O

I designed a new fan mount and rewired the fan to eliminate any possibility of that happening again and my printer's back up and running. BUT. now I have no control over the fan speed. Nothing I've tried can even turn it off - I might as well plug it in to the fan 2 pins instead of d9. 

Google and reprap forums suggest a fried MOSFET pin which, given my observations, I'm inclined to agree with. Beyond that I have no clue how to fix it. I have some soldering experience and I'm willing to try to replace/repair but would be very grateful if anyone could step me through exactly what I need to do to get PWM back for my part fan. Or point to any helpful resources.

Many thanks


  • Well a short might in deed destroy mosfet or even the avr chip on ardino so that the pin is not switchable any more. They are quite sensible so single pins can get a defect easily. So if you use no bed you could use that output for fan. There is also a fan extender you can put on the ramps board. Or replace the ramps board. They are quite cheap nowadays so I would not waste too much time on fixing a defect one.
  • Would putting a fan extender on a blown mosfet be any use? Sorry for my ignorance here. I'd rather fix a single part or find some workaround than replace the whole board if possible.
  • The fan extender uses other pins on one of the AUX ports so it does not use that part of the board. 
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