[Mike Betts]

Andy,

One or both of your motors may be shorting to frame internally. It's also possible that a motor has a shorted winding. In either case, this would cause momentary shorts as the motor is rotating which would cause high voltage spikes when the rotor moves past the short.

High voltage spikes will certainly kill the IGBT drive in the victors but not right away (it's cumulative damage to the silicon substrate). If so, it's hard to "logically" tell which side is causing the problem.

High voltage and current spikes will also create EMI noise which you also seem to be seeing.

I have never seen this on a FIRST system but I have seen it on larger motor drives we use at work.

I would replace both of the motors.

That's my best scenario...

The only other idea I have is that a wire's dielectric insulation is breaking down (either to chassis or to another wire) between one of the Victors and the motors. However, this is not very likely (we use 300V wire).

Good luck!