One common problem is your microwave not heating up and the most popular reason behind this issue is magnetron failure. If the microwave is turned on when it is empty, this cause the magnetron to burn out. This can only be fixed with a replacement magnetron, they cannot be repaired. Sometimes microwaves stop and start, this can be due to a faulty door switch which can be adjusted yourself most of the time, thus can also be due to a defective touch pad and faulty fan motor.
In a microwave there is a rotating motor below the plate which is responsible for the rotation of spinning plate. The most common reason for this not working is a worn out motor which can easily be replaced. However, if the motor is not defective this indicates a fault in the main control board.
There is sometimes a sparkling that takes place in the microwave when there is a problem. Possible reasons behind this problem are damaged wave guide cover, diode burn, damaged rack support or worn out paint from the inside walls.