Step 8: Repairing the Control Board: Checking the Diodes
With the DMM still set to the Diode-check range, check each one of the large Power Diodes on the other side of the board (see pic) the following way: Connect the DMM probes to each end of the diode and look for an open circuit indication (no indication) or a diode indication (an indication of somewhere between 0.4 and 0.6). Then reverse the probes and check for the opposite indication to the one before. If any of the DMM readings indicate a short, or an open in both directions, the diode is faulty; and must be replaced. Check all power diodes. I never found any of the smaller diodes faulty, but if all else fails to repair the board, you will need to check these too. On the last repair, all four diodes in the bridge configuration feeding the electro caps had blown, all cracked open, and part of the PCB track had vaporized.