How to Test a Microwave Magnetron

Categorized as Microwave Repair and Troubleshooting
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A microwave oven is one of the most used appliances in most homes today. It offers a quick and convenient way to reheat, defrost or cook food. However, like any other home appliance, the microwave can develop faults over time. One of the most common issues is a faulty magnetron.

The magnetron is responsible for generating the microwave energy that cooks or heats the food. When it fails, you will notice the microwave power reduces significantly or stops heating altogether. Before replacing this crucial component, it’s important to accurately test and confirm the magnetron is faulty.

This guide provides a step-by-step walkthrough on how to properly test a microwave magnetron using a digital multimeter (DMM). We also cover safety tips, magnetron basics, troubleshooting steps and frequently asked questions.

What is a Magnetron and How Does it Work?

The magnetron is essentially a high-powered vacuum tube that converts electrical energy into microwaves using electromagnetic radiation. It consists of:

  • A cylindrical anode (positive electrode)
  • A cathode (negative electrode) filament
  • Permanent magnets surrounding the filament
  • Antennae to emit the microwaves

Inside the tube, the cathode filament is heated to release electrons. The electrons are then attracted to the positively charged anode but get deflected by the magnetic field. This results in the electrons spinning around rapidly and generating high-frequency electromagnetic microwave energy.

The microwaves are channeled through the antenna into the oven cavity where they agitate and heat up food molecules. The magnetron needs high voltage (around 2000V) from a transformer to operate.

Safety Tips When Testing a Magnetron

Working with a microwave and its high voltage components can be dangerous if safety precautions are not followed:

  • Unplug the microwave – This should be the first step before opening or working on the appliance. Ensure it’s unplugged at all times during testing.
  • Discharge capacitor – The high voltage capacitor holds dangerous levels of electricity even when unplugged. Discharge it safely using an insulated resistor.
  • No power – Do not have the microwave plugged in when testing the magnetron.
  • Avoid microwave radiation – Never operate the oven with an open door or damaged door screen. The radiation can be hazardous.
  • Don’t touch components – Many parts like the capacitor, diode, transformer and magnetron itself can give dangerous electrical shocks.
  • Use insulation – When necessary to touch components, use insulated tools and gloves to avoid shocks.
  • Reassemble properly – Once done, refit the case and parts correctly to prevent microwave energy leakage.

How to Test a Microwave Magnetron

To properly diagnose a faulty microwave magnetron, you need:

  • A digital multimeter capable of measuring ohms, voltage and continuity
  • Basic toolkit including insulated screwdrivers, gloves, etc.

Follow these steps:

1. Unplug Microwave and Discharge Capacitor

Unplug the microwave from the power outlet. If there is an in-line fuse, remove it as well.

Use a 20,000 ohm, 10 watt resistor to safely discharge the high voltage capacitor. Touch the resistor leads across the capacitor terminals until it is fully discharged.

2. Remove Outer Case

The magnetron is located on the top or side of the oven cavity. You’ll need to remove the outer case to expose it. The case is held in place with screws or plastic tabs.

Be careful when removing the case – the inner components and wires are still connected. Avoid tugging too hard.

3. Locate and Label Magnetron Wires

The magnetron will have 2 or more wires connected to terminals on its body. These include:

  • Filament wires – Heats the cathode filament and usually labeled F1 and F2.
  • Antenna wire – Emits microwave energy into oven.
  • High voltage wire – Provides 2000V to 4000V DC from the transformer.

If loose, label these wires so you can reconnect properly later. Detach the wires if necessary but remember their positions.

4. Check Filament Continuity

Set your multimeter to the continuity or ohms setting. Touch the probes to the two filament terminals – you should get a reading around 1 ohm. This confirms filament continuity.

If no reading or infinity, the filament may be burnt or broken. Note – older magnetrons may have more than 1 filament.

5. Test Filament to Chassis Resistance

Now set your multimeter to the lowest resistance range, usually 200 ohms. Place one probe on a filament terminal, and the other probe on a metal ground point like the chassis.

You should get a very low resistance, usually below 1 ohm. Higher than a few ohms indicates a short circuit, while infinity means an open circuit. Repeat test for the other filament terminal.

6. Check Antenna Continuity

Test continuity between the antenna terminal and chassis ground. You should get 0 ohms. If no continuity, the antenna coil is likely damaged.

7. Measure High Voltage Terminal

Finally, switch your multimeter to the highest resistance range, usually 20M ohms. Test between the high voltage terminal and a ground point.

A healthy magnetron will show no continuity, indicating an open circuit. Any reading means a short circuit, and the magnetron is faulty.

If all tests check out fine, the magnetron is likely working properly. Reassemble the microwave and test. If it still doesn’t heat, the issue may lie elsewhere like the high voltage components.

Troubleshooting Magnetron Issues

Here are some common problems and troubleshooting tips if your magnetron tests reveal issues:

No heating, low power:

  • Burnt or broken filament – Check filament continuity. Replace magnetron if open circuit.
  • Loss of emission – If filament is ok but resistance tests show shorts, emission ability is reduced. Replace magnetron.
  • Faulty high voltage components – Check diode, capacitor and transformer if magnetron tests fine.

Noisy operation, humming:

  • Failing filament or cathode – Conduct resistance tests between filament and chassis to diagnose.
  • Arcing in tube – Carefully inspect magnetron for dark burnt marks indicating arcing. Replace if present.
  • Bad mounting – Check magnetron is positioned properly on chassis. Tighten mounting screws.

Overheating, burning smell:

  • Blocked cooling vents – Ensure clear space around oven for ventilation. Clean out obstructions.
  • Failing magnetron – Short circuits in tube can lead to overheating. Conduct resistance tests.
  • Improper door seal – Check condition and fit of door gasket. Replace if loose or damaged.

When to Replace a Magnetron

In most cases, if the continuity and resistance tests indicate any results other than the expected values, the magnetron will need replacement.

Some signs that clearly confirm a faulty, end-of-life magnetron:

  • Visible cracks, burns or damages on the magnetron body.
  • Open circuit in the filament when checking continuity.
  • Short circuit between filament and chassis.
  • Zero ohms resistance between high voltage terminal and ground.

To extend the magnetron lifespan, avoid operating an empty microwave, keep the vents clear of dust and debris and don’t exceed the oven wattage.


What tools do I need to test a magnetron?

You will need a digital multimeter, an insulated resistor (10k ohm 10 watt), insulated gloves, basic toolkits including screwdrivers, wire cutters, etc. Use insulated tools when possible.

How can I tell if my magnetron is bad?

If the microwave is not heating, check for a faulty magnetron. Visual signs include burns or cracks on the tube. Use a multimeter to test filament continuity, resistance values and antenna continuity as explained.

Can I repair a magnetron?

No, if a microwave magnetron is found to be faulty through testing, it cannot be repaired and needs complete replacement. Do not try to service or fix the magnetron yourself.

What happens if I operate the microwave without the magnetron?

Without the magnetron to generate the microwaves, the oven will not be able to cook or heat anything. Operating it like this could also damage other components.

How much does it cost to replace a magnetron?

The replacement cost for most microwave magnetrons ranges from $30 to $180. The exact price depends on the specific oven make and model. Match the part number when ordering a replacement.

What safety precautions should I take?

Always unplug the microwave and discharge the capacitor before testing. Use insulated tools, don’t touch components unnecessarily, avoid microwave radiation exposure and reconnect parts correctly.


Testing a microwave magnetron is an essential troubleshooting step if you suspect a fault. While not overly complicated, it does require care and the right tools. Follow the continuity and resistance test steps outlined above to accurately diagnose the magnetron.

Pay close attention to the expected readings versus the actual values. Refer to the troubleshooting tips if you encounter any issues while testing. And replace the magnetron promptly once confirmed to extend the life of your microwave.

By Rosie Elliott

I’m Rosie. I’m a professional chef with experience in Western, Mediterranean, and Italian cuisine. I’ve been cooking for over 15 years, and I have two daughters that keep me busy!

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