I know this is an old topic... but I managed to blow the F2 fuse today. I connected one of the pwm fan connections to a proto board via the pins so I could use it to connect some LED's separately with a soldered connection to the proto board and not have to solder on the duet wifi. I noticed that the fans stopped working after that. I checked continuity with all the pins prior and there were no shorts but i must have missed something that caused it to short. That is my guess, but it was directly related to connecting a pwm fan connection to a proto board that just has other pins soldered onto it in a series.