Today I've been trying to verify the Fan Control FET circuit so that the board can be finalized. So far it will only work at 100% duty cycle. I've tried different things but always partial duty cycles cause immediate restart/shutdown. I added a resistor from the PIC output to GND to ensure the FET gate drops to GND when off, but no better. I just have a generic cheapo 3 pin fan and usually they can be controlled with PWM, according to my reading online, but perhaps some are different. (Note I'm not talking about PWM control in the fan like 4 pin fans, but just switching the 12V line with PWM.) I based my circuit off another well known working one so this is odd. I'll keep working on it.
I did this in my miner with an optocoupler and a power transistor (2955 but that is overkill). PWM controls the cheapo fans just fine, I'm only use 2 pins per fan, relying upon temperature to set the PWM rate with no feedback.