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 symptoms a bad magnetron causes, what the magnetron’s purpose is, and a simple test you can perform to confirm the magnetron is fulfilling that purpose.
Microwave Not Heating? The Magnetron Might Be the Culprit
If your microwave is not heating, a faulty or bad magnetron is often the root cause—especially when the high-voltage system is involved. While other parts like a door switch, line fuse, or control board can fail, the magnetron is the component most directly responsible for generating microwave radiation to heat your food. When it stops working, the microwave may appear functional—lights on, turntable spinning—but no actual heat is produced.
If you’re wondering how to test a microwave magnetron, how to check a magnetron, or how to tell if a microwave magnetron is bad, the first step is understanding the common symptoms of failure.
Signs of a bad or faulty microwave magnetron include:
- The microwave runs, but doesn’t heat up
- A burnt electrical smell
- Loud humming, buzzing, or high-pitched growling noises during operation
These bad magnetron symptoms indicate the part may no longer be producing the electromagnetic waves required for cooking. If you’re wondering what to do next, it’s time to learn how to check if your microwave magnetron is working—starting with a simple multimeter test.
How to Check If Your Microwave Magnetron is Working
One of the most effective ways to verify if a magnetron is the reason your microwave isn’t heating is to test it for electrical continuity and resistance using a multimeter. This is a safe and reliable method for testing microwave magnetron components, especially if you’re researching how to test magnetron with multimeter or how to test microwave magnetron accurately. But before jumping into the hands-on portion, it helps to understand the magnetron’s role in the microwave—and why high voltage safety measures are absolutely essential.
Understanding the Magnetron’s Role in a Microwave
What does a magnetron do in a microwave? 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.
Now that you understand the magnetron in microwave systems, it’s clear why a microwave not heating up often points to a faulty high-voltage component.
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 test for electrical continuity. This magnetron continuity test confirms whether a continuous electrical path is present. If you’re asking, “Can you test a microwave magnetron?” the answer is yes—with care. 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 a Magnetron in a Microwave: Step-by-Step
This section explains exactly how to test a magnetron in a microwave, with emphasis on performing a magnetron continuity test and ensuring safety throughout the process. It also covers how to check magnetron resistance and identify shorts to ground.
Magnetron Continuity and Resistance Testing Explained
Before proceeding with the actual test, it’s important to understand how magnetron continuity and resistance testing works. A properly functioning magnetron should display between 0 and 5 ohms of resistance between its two terminals when tested with a multimeter. This indicates electrical continuity. If your multimeter shows an infinite reading, the magnetron is open and will need to be replaced.
Additionally, you should check for a short by placing one probe on a terminal and the other on the metal casing. If there’s continuity here, the magnetron is shorted to ground—another indication it has failed. Understanding these principles ensures you can test a microwave magnetron accurately with a multimeter and avoid misdiagnosing the issue.
How to Test a Magnetron with a Multimeter
The most reliable way to diagnose a faulty magnetron is to perform a magnetron continuity test using a multimeter. If you’re wondering how to test a magnetron on a microwave, here’s how to test a magnetron, that you can follow to test the component for electrical continuity:
⚠️ Important Safety Warning: Unplug the microwave and discharge the capacitor before beginning any repairs. Microwaves contain dangerous high-voltage components.
Steps for Testing a Magnetron:
This step-by-step covers testing a magnetron with multimeter:
- Access the Magnetron
On some models, you can simply remove the control panel. Others may require removing the microwave from above the range and taking off the full outer shroud. Always work safely and consult your owner’s manual if needed. - Discharge the Capacitor
Use an insulated tool to short across the capacitor terminals, even if it has a bleeder resistor. - Disconnect the Wires
Remove the wires from the magnetron’s terminals. - Set the Multimeter
Turn the dial to the lowest resistance setting (ohms). - Test for Continuity
- Contact the black meter lead to one of the magnetron’s terminals and the red meter lead to the other terminal.
- 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.
- Check for Shorts to Ground
- Touch one probe to a terminal and the other to the magnetron casing.
- Any reading (other than infinite) suggests the magnetron is shorted and must be replaced.
*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.
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 replacement microwave magnetrons for popular models from 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
Along with genuine parts, Repair Clinic offers a deep library of videos and articles to show you how to fix your microwave and replace the magnetron safely. Whether you’re troubleshooting a microwave not heating issue or looking to understand how to check if magnetron is working or not, we’ve got the answers. Search Repair Clinic’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.