Nice engine! I do not have one so I cannot be very specific. If it were mine I would first suspect a failure in the circuit board or rectifier added to run the DC motor from the AC track power. To determine if this is the case disconnect one of the motor leads from the circuit board and use a DC source connected to the two motor leads and see if the motor runs. Any DC source 4V or higher is OK. If the motor works then the problem is the circuit board.