Given that the screw that holds the tail motor mount to the tail boom has caused problems in the past, I visually checked the wire for the tail motor runs through the plastic tail mount . I removed the screws at the tail motor mount and removed it from the shaft, but did not observe any damage to the wires inside. I have a DMM and will measure the resistance of the leads to the motor to look for a short.

I tested the 3rd (as well as 1st with loose connection and 2nd) motor with a 6V battery pack to see that it operates as expected with power. Thus, it was not a bad 3rd motor.

Perhaps, heating of the motor connections during soldering/replacement damaged the E-board resulted in a short internally or to the case. In hindsight, I should have removed the connection from the E-board to the motor before soldering the new tail motors to the wiring. However, I thought that the motors were burning up, not the E-board until yesterday.

How do I check that the capacitor (on the motor, right?) has not somehow shorted or it's leads have?