File talk:PrintBedCircuit.png

In the Sanguinololu 1.3a the Hot End and Bed 12V pins are not switched, the Ground is switched. Please see Sanguinololu 1.3a schematic. With this schematic the FET will be on all the time. I have tried this circuit with the power to the heater resistors from a bench power supply. In this setup although there is Ground from the bench psu and Ground from the Sanguinololu they are different Grounds. Next try with a spare PC PSU for the second 12V supply. Advice in Longboat instructions was to cut tracks to isolate the MOSFET on the Sanguinololu. Unfortunately there was no schematic. I prefer to add some stuff rather than hack and slash the already assembled board.