I have a Printrbot simple metal with factory extended x axis and heated bed upgrade, F4 board, many, many hours of successful printing. All of a sudden on power up Q2, the MOSFET controlling the heated bed, gave up the smoke burning up the traces and what I assume is part of the ground plane on the back of the board. I could use some help figuring out how to fix this. I measure about 1ohm resistance in the heating element and can not find it shorting anywhere. The thermistor measures 93 ohms. I am using a 30a 12v power supply. I did not have the right MOSFET on had to switch out. I had a RAMPS 1.4 board that I got for less than shipping on a new MOSFET would cost so I decided to connect it knowing I might smoke it. I was right. As soon as I powered it up the hot bed MOSFET got hot enough to loosen the solder joints. Just to make sure the bed heat plate wasn't somehow shorting to the print bed, I removed the bed and put it on a wood surface on nylon standoffs. Same thing exact thing. I'm not sure what to test next. Any help is appreciated.
thanks