Williams Black Knight (Williams, 1980) F2 fuse blowing

[boydsc331]

hello i just bought a Black Knight project machine. it blows the i think its F2 fuse. its the middle one on the fuse card. if i unplug every connector on the power supply board except the 2 power input plugs it still blows that fuse. so i think its something in the power supply board ? is this right ? and if so what should i look at next ? its the earlier bk with the sys 6 boards not the sys 7 boards

 

[pinballdaveh]

a way to test this is to unplug machine, unplug all the connectors on the power supply. remove F2 fuse. using a dmm on resistance beep range, test from ground to each fuse clip. any beep tone means that there is a board short. unplug the ac in wires on the solenoid bridge rectifier, and test for a shorted diode on the bridge rectifier lugs. diodes have polarity and some resistance in one direction only. please post results of your findings.