Quoted from Brewchap:
I found the picture on Pinwiki web site. Credit goes to Chris Hibler.
I measured and tested my last bridge rectifier. It tested good like it should. I installed it and powered it up. The MPU still will not boot. So I tested the BR2 again and it's bad again. Something must be shorting it out. It reads the same as in post #6
The bridge shouldn't go bad like that and I would be surprised if two failed the same way. Bridges normally fail short circuit and blow the fuse. They can fail open circuit too... but i think they usually fail short first then burn open.
How are you testing the bridge? For testing bridge DMM on diode test. Red DMM lead to negative bridge terminal then probe to both AC ~ pins and you should see a normal 0.4-0.6v voltage drop. Then do the opposite on the other side. Black DMM lead to the positive bridge terminal and probe both AC ~ pins and you should see the voltage drop.
How about a bad driver board C23 filter cap dragging down the 12v? Can you try with the top right connector on driver board removed and see if the voltage comes up?