To repair a microwave motor, locate the motor under the bottom panel of the unit, use a continuity tester to determine if it's still functioning, and replace the motor if necessary. If not, replace only the damaged wires that impede the motor's functionality.
When using the continuity tester to examine electrical contacts on the motor, check if the tester lights up. If the motor is dysfunctional, the tester does not light up, indicating that a motor replacement is required.
To start, remove the turntable and frame in the microwave. Unscrew the bottom panel, and disconnect its wiring harness to remove it. Locate the motor under the panel, and determine its part number to purchase the correct replacement. Unscrew, disconnect and remove the old motor, and then replace it with the new one. Reconnect the wires in the new motor, and screw the motor into place. Reassemble the bottom panel, frame and turntable of the microwave, and then test for proper functioning of the motor.
If the continuity tests light up through the motor, this implies the wires connecting the motor to the unit are damaged, causing the motor's functionality to be impeded. In this case, replace only the frayed, oddly bent and dislodged wires.