Help with Victor 884s

[indieFan]

This past Saturday, the team hooked up last year's Victors to this years trannys. (4 motors, each to their own Victor.) Immediately after turning the power on, there was sparking and a cracking sound. We shut power off, pulled the PWMs out of the two Victors that were the problem, and pulled all of the wires from these same Victors. We turned power on to test the other tranny, but the Victor(s) with no wires sparked and made the same cracking sound. On the wooden board, the Victors were mounted so that they were all butted up against one-another.

1. What would have caused the Victor(s) to spark with no wires going to them?

2. When I looked at the two Victors, one of them had the plastic at the base of three FETs on one side that were cracked through. Is it likely that other components on this Victor were blown, or is it just the FETs? (I opened the Victor and cleaned it with IPA.) The second Victor didn't have any cracks near the FETs, and I didn't open it.

Thanks,
indieFan