[rfolea]

Are you using dual motors per gear box with Y-Cables?

If so, are the Victors set to BRAKE?

If so, then this might be caused by a bad Y-Cable connection.

Motor A is on BRAKE because it is getting no signal, while motor B is trying to move forward and they end up fighting each other, drawing lots of current and popping FETs.

Disconnect the motor leads and run the joystick around and make sure the Victor lights all agree before reconnecting the motors.