Maintenance method:we should first distinguish whether it is a circuit failure or a mechanical failure.
(1) Step on or lift the reverse switch pedal to observe the reaction of the motor. If there is no response, use a Multimeter to measure the reverse switch which helps to check whether the voltage between the terminals is normal. If the voltage is abnormal, we should check the power supply line or power plug. If the voltage is normal, use a Multimeter to measure whethr the voltage of inverted switch terminal and terminal when stepping on and lifting the power switch pedal is normal. If it is not normal, it indicates that the reverse switch is bad. If it is normal, the motor or the capacitor is bad.

(2) If the motor has a hum, but can not turn, the measurement method is the same as above. If the measurement result is not normal, the reverse switch is bad. If normal, turn the transmission pulley by hand. If you can not turn it by hand, the transmission is faulty. If you can turn by hand, it is a motor or capacitor failure.
(3) If the motor can rotate normally and the working round plate does not rotate, it should be a transmission failure. For example, the transmission pulley does not drive the worm to rotate and the worm wheel collapses.