We have found that different parts of of our robot that are isolated from other components of the robot with nylon spacers have the issues. If there is a motor in the isolated section, and it is only connected to the main part of the robot through the wire running the motor it tends to blow a port. You can check for potential voltage differences with a multi-meter. We have bonded the isolated components of the robot together with a stand of the jumper stock (my not be competition legal) and the issue with blowing ports went away.
