Microwave Magnetron Testing

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A microwave’s magnetron is one of the most important components in the handiest appliance you have in the kitchen. But what a magnetron does and, more importantly, how to determine when it isn’t doing what it’s supposed to do, can sometimes seem like a mystery. Repair Clinic will try to clear up that mystery by reviewing what the magnetron’s purpose is and a simple test you can perform to confirm the magnetron is fulfilling that purpose.

A microwave magnetron’s purpose

The microwave magnetron is the component most directly responsible for heating up the food placed in the microwave and the part needs a lot of voltage to function.

The magnetron needs a lot of voltage to function

Once a designated power level option and cooking time are selected on a microwave, pressing the start button will cause the appliance’s control board to send 120 volts of alternating current (AC) through a line fuse, a cavity thermostat, and multiple door switches, before the current reaches a high voltage transformer. A high-voltage capacitor works with a diode to convert the alternating current power output of the transformer to direct current (DC), doubling the voltage to nearly 5,000 volts. This increase in voltage is what is required to power the appliance’s magnetron.

The magnetron emits electromagnetic waves which cook the food

Once energized, the magnetron emits electromagnetic waves which travel through a waveguide before entering the oven cavity. As the food rotates on a turntable in the oven cavity, the electromagnetic waves cause water molecules within the food to vibrate intensely, generating heat that cooks the food from the outside in.

What happens when the magnetron malfunctions?

Simply put, without the electromagnetic waves bouncing around the microwave oven cavity, the item placed in the microwave will not heat up, so a malfunctioning magnetron can put an end to your hopes of quickly warming up those leftovers for a midnight snack. While there are other components that can cause a microwave oven not to heat such as a faulty door switch, a blown line fuse, or even a defective control board, many times a high voltage system component like the magnetron is responsible for the heating problem.

How to tell if the magnetron is malfunctioning

How can you determine if the magnetron is, indeed, malfunctioning, and not the diode or the high-voltage transformer? One way is to use your ears. Since the magnetron uses high voltage to generate the electromagnetic wave frequency to cook the food, you should hear a low hum when the magnetron is working. However, if the magnetron is damaged or nearly burned out, it may begin emitting high-pitched sounds or growling noises. A more conclusive way to determine if the magnetron has failed is to use a multimeter to determine if the component has electrical continuity – a continuous electrical path present in the magnetron. To do this, you will need to partially disassemble the microwave and that requires an important warning…

Always put safety first when disassembling a microwave

To access the magnetron for testing on some models, you will just be required to remove the control panel. For other models, you will need to remove the appliance’s entire shroud or cover and this may require fully uninstalling the microwave if it’s installed above a range and acts as a venting system for the range’s cooktop. In either case, you will need to put safety first:

Because of the high voltage and high current used by microwave ovens, be aware that repairing this appliance poses a substantial risk of injury or death if precautions are not taken. You should always unplug the microwave before you attempt any disassembly. High-voltage capacitors used in microwaves have the potential to shock and this is the reason we stress that only experienced professionals access and replace internal components.

Make sure the microwave capacitor is discharged

If you do need to access internal components, you should make sure the capacitor is fully discharged immediately after removing the microwave’s shroud or cover. While most high-voltage capacitors used in recent microwave models have a bleeder resistor in them that should automatically discharge the capacitor after the voltage has been discontinued, it’s always a good idea to confirm this by attempting to discharge the capacitor manually. This can be done by placing a screwdriver blade or needle-nose pliers across each set of capacitor terminals. The handle of the screwdriver or pliers should be insulated, and you should avoid touching the metal portion of the tool when the tool is in contact with the terminals.

How to test the magnetron for electrical continuity

Once you’ve accessed the magnetron, here are the 4 steps you can follow to test the component for electrical continuity:

  1. Disconnect the wires from the magnetron terminals.
  2. Rotate the multimeter’s range selection dial to the lowest setting for ohms of resistance.
  3. Contact the black meter lead to one of the magnetron’s terminals and the red meter lead to the other terminal.
  4. Observe the multimeter display. If the meter display shows a reading between zero and five ohms of resistance, the magnetron has electrical continuity and should be functional*. However, if the meter display doesn’t change at all, the magnetron has no electrical continuity and will need to be replaced with a new one.

*There is a caveat here. Even if the magnetron tests positive for electrical continuity, the part could still be malfunctioning if all the other high voltage components (diode, capacitor, transformer) test positive for ohms of resistance.

Microwave Magnetron Testing

Repair Clinic stocks genuine OEM microwave parts

As your repair partner, Repair Clinic believes you should only use the genuine manufacturer parts intended for your appliance, which is why we only stock genuine OEM replacement parts that match the most popular microwave models, including those manufactured by GE, Samsung, Whirlpool, LG, Kenmore, Frigidaire, and Panasonic. How can you find the right magnetron that fits your microwave? Enter the full model number of the unit in the Repair Clinic website search bar to see a comprehensive list of compatible parts. You can then use the “Part Category” filter (“Diode, Magnetron & Resistor”) along with the “Part Title” filter (“Magnetron”) to identify the specific part you need.

Repair Clinic provides the know-how to fix your microwave

In addition to providing you with genuine OEM parts, Repair Clinic provides you with the know-how to help you fix your microwave. Search the website’s “Videos & Articles” library to find schematics, step-by-step guides, and “how-to” videos that will show you the proper way to install a new magnetron in a Frigidaire Microwave (model FPMO227NUFA) or how to troubleshoot a microwave that’s not heating.

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