Microwave problems

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Microwave Not Working or doesn't heat

Line Fuse

Every microwave oven has a line fuse. This fuse is designed to blow if too much current is drawn through the microwave circuitry. The fuse can be replaced, but the underlying issue should still be investigated and resolved. Otherwise the new fuse will blow also.

Main Control Board

If the microwave is not working the main control board may be defective. This is not common. When a microwave stops working the problem is usually the line fuse or within the high voltage circuit; either the high voltage capacitor, diode, transformer or magnetron.

Thermal Fuse

If the microwave is not working the thermal fuse may have blown. It can be tested for continuity. Watch our fuse testing video for more information.

Thermoprotector

If the microwave is not working the thermoprotector may have tripped. This is a safety device to prevent the microwave from overheating. It can be tested for continuity to see if it’s blown.

Diode

The high voltage diode converts the A/C power output of the transformer to D/C, doubling the voltage to nearly 5,000 volts. This high voltage powers the magnetron which emits the energy that cooks the food. If the diode burns out, a lower A/C voltage reaches the magnetron, which is not sufficient to power the magnetron. When the diode fails it is often visibly burned out. If it appears to be good, it can be tested with a volt-Ohm meter capable of testing diodes. High voltage diodes frequently fail and are one of the most common points of failure in a microwave oven. A regular meter with a diode checker will not work to check these diodes. You have to use a meter with a 9 volt battery or put a 9 volt battery in series with the diode to check it.

Door Switch

If the microwave does not heat, one of the door switches might be defective. Microwave ovens normally have three door switches, if any of them fail the microwave does not turn on and does not heat. Check the switches for continuity with an Ohm meter.

Magnetron

If the microwave oven doesn’t heat the magnetron tube might have burned out. The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. If the microwave oven is turned on when it is empty this can cause the magnetron to burn out. Once it is burned out it has to be replaced, it’s not repairable.

High Voltage Capacitor

If the microwave doesn’t heat the high voltage capacitor might be defective. The high voltage capacitor works with the high voltage diode to convert the output of the transformer to DC voltage and to double the output voltage. If the capacitor is burned out the entire high voltage circuit stops working properly. The high voltage capacitor can be checked with a special VOM meter which has a capacitance testing capability. Be aware that the high voltage capacitor can retain a charge of more than 3,000 volts and can injure or kill a person if not handled properly. Only trained technicians should perform this type of testing.

High Voltage Transformer

If the microwave does not heat, the high voltage transformer might be burned out. Microwave ovens produce a very high voltage in order to power the magnetron antenna, which emits the energy that cooks the food. When a high voltage transformer fails it will usually arch and have a burning smell.

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