Victor Burnouts

[Al Skierkiewicz]

Mark,
Foreign objects leave little parts of themselves in and on components. An inspection under a bright light will usually reveal an arc mark (burned deposit) on a component leg or on the board.
Brake mode should not have any adverse effects unless a controller was in brake for a full match while other motors were back driving it while running. To my knowledge, brake mode turns on the lower half of the "H" bridge thus putting a short on the motor through the two bottom sets of FETs. As you suggested earlier, the FETs died in one line, I took that as one set of positive FETs and one set of negative FETs, the two of which are in series through the motor.
If the controller is trying to push a lot of current, then there might be a domino failure. The first FET just pops and then the second and third have to share the current. When one of those fails, the last one is suddenly running all the current and blows it's case apart as there is no place for the magic smoke to go. If the controller were wired backwards, it is possible but I think unlikely, that FETs could be turned on across the battery input. They might be able to fire up in reverse polarity under these conditions and the failure might be instantaneous vaporization of the internal wiring causing an open FET. I think that the power input is reverse polarity protected but the motor output cannot for obvious reasons. That would also explain why only two sets of FETs were failing and not all four.