If a microwave appears to be operating but does not heat food, the problem could be a bad diode, high voltage capacitor or magnetron, according to RepairClinic.com. Microwave ovens are high-voltage electronic equipment that can cause electrical shock even when unplugged from the power. Consumers should proceed with caution when opening the cabinet.
A diode serves as a one-way switch for electrical power. By preventing the power from flowing back through the circuit, it converts alternating current to direct current. In the process, it doubles the voltage to the almost 5,000 volts the unit requires to power the magnetron and heat food. If the diode is defective, it often has a burnt appearance on the outside, and attempts to operate the microwave result in a loud buzzing sound.
Microwave ovens also use high-voltage capacitors to heat food. The capacitor stores electrical energy. A defective capacitor interrupts the high-voltage circuit the unit requires to heat food. It is essential to discharge the capacitor before handling it. The capacitor in a microwave oven stores up to 3,000 volts and can cause bodily injury or death with improper handling.
The magnetron converts electrical energy to microwaves. If it burns out, the oven does not heat. Operating an empty microwave oven can cause the magnetron to blow. A blown magnetron is not repairable and requires replacement.