What Causes a Magnetron to Fail in a Microwave?

Every microwave oven has gone through a problem of not heating the food in the oven at some point of time while cooking. But have you ever thought of why it happens so? What Causes a Magnetron to Fail in a Microwave?

If you know the answer then, Yes, It’s because of the damage caused to the Magnetron in the microwaves oven.

But, Do you know what causes the magnetron to fail in a microwave oven? Well, there are many reasons behind it to cause a magnetron to fail in a microwave oven. They are Magnets Cracking, Burned out terminals, Burned antenna/dome, a loose connection of magnetron, Resistance continuity. …etc.

Some of the causes are visually seen and some are known only by testing. If you are interested in further details of the causes then travel with us by swiping up the page.

What Causes the Magnetron to Fail in a Microwave

There are some causes which cook the food in a microwave oven with less heat or no heat. On that account, Check for the causes which make magnetron to fail.

And this is how a magnetron looks like.


Magnets Cracking

This cause happens when the damage occurs to the magnets of the magnetron, this results in reducing the magnetic field.

And overheating of the magnets also causes damage to the magnets in magnetrons. The cause for overheating is due to the microwaves reflecting back the back to the magnetron.

Burned out terminals

The insulator in the magnetron helps to insulate the whole magnetron from being attacked by the direct voltage. But if any damage happens to it will lead to the insulator breakdown.

This insulator breakdown results in burning the terminal of the magnetron. It increases in every cooking cycle and leads to severer burnout.

Burned Antenna/Dome

We can see an antenna/dome of the magnetron in the microwave oven at the inside of the filament box. The reason for causing damage to it is reflecting back of the microwaves while cooking.

These reflected microwaves cause damage to the antenna/dome of the microwave oven by stopping it to send the microwaves.[amaplug_bestseller keyword=”microwave magnetron” style=”Popup (Bottom)” items=”5″ max=”10″ location=”com”]

Loose Connection of Magnetron

This is the common cause that happens to the magnetron. This loose connection leads to high resistance heat. This heat will burn out the other parts adjacent to the magnetron and results in forming black spots, burn marks on the damaged area.

Resistance Continuity

As the above causes are physical to observe, this resistance continuity belongs to the testing process.

This test is to check between the terminals of the magnetrons with an ohmmeter.

Before testing, you need to unplug the power terminal of the microwave oven.

By attaching the ohmmeter, the continuity of the resistance should be infinity. If the reading is other than continuity then there is something wrong with the magnetron in your microwave oven.

Check out the video for a test with multi-meter

Click here for video

Arc-over internally

This happens when there is a gas formation inside the magnetron. If the gas is present inside the magnetron it will give an arc-over internally when the power is applied suddenly.

Symptoms to Observe When a Magnetron is Failed:

Here are some symptoms to observe when a magnetron fails.

  • No heating
  • Burning smell
  • Arcing sounds
  • Snapping sound

Deceases in heating and stops before ending

If you observe these symptoms while cooking food in the microwave oven the immediately stop the oven by unplugging the main power supply and it’s time for you to replace/repair the magnetron.

But what is better to replace/repair the magnetron in the microwave oven

Check out the video of spotting bad magnetron.

Click here for video

Replace/Repair the Magnetron

It always depends on the amount of damaged that happened to the magnetron. So, it better to detects the problem first before choosing to replace/repair. As magnetron costs much to purchase, it’s ok the problem is repairable, if the problem is severe then you need to change the magnetron by purchasing the new one.

Sometimes the improper repair can raise the same problem again.

If you want to replace the magnetron with a new one make sure that is done by a professional technician. Because a residue of the power will remain in the magnetron which can lead to shock.

But do you know how actually a magnetron works? Let us know the role of the magnetron in a microwave oven.

How Does Magnetron work?

Generally, the microwave converts the electric energy into the microwave with the help of a magnetron.

What Causes a Magnetron to Fail in a Microwave

This magnetron is a vacuum tube with a cathode rod at the center surrounded by a hollow anode rode with cavities in it.

On the pass of electricity, the electrons heat up the cathode rod. The heated cathode rod excites the electrons to the anode.

There the electric filed along with a perpendicular magnetic field also exists. So, due to the magnetic field, the excited electrons tend to move towards the anode in a curved way instead of straightway.

These curved electrons tend to resonate with the cavities of the anode.

Theses resonation happens at the frequency equal to the frequency of the microwaves.

Thus the microwaves are produced for the magnetron from the antenna.

How Microwave Cooks Food?

Mainly the parts of the microwave oven are

  • Magnetron
  • Waveguide
  • Stirrer
  • Turntable

The produced microwaves will travel to the inner cooking chamber through the waveguide.

A fan-like stirrer will spread the microwaves al around the cooking chamber.

Due to the reflecting material coating of the walls, the microwaves get reflected.

This reflection then forms a to and fro motion of microwaves and finally penetrates into the food with water molecules on the turntable.

The water molecules in the food are dipolar and tend to vibrate with the microwave penetrations.

The food in the microwave oven thus gets heat up with the vibration of water molecules.


Finally, it is you to find out the symptoms of the magnetron damage and to turn it off immediately. Think twice to repair the magnetron as this will again lead to damage within a short time after improper repair

Periodical maintenance is the best option to overcome all the causes that happen to microwave including the damage of magnetron.

Frequently Asked Questions:

Can you fix a microwave that doesn’t heat? Yes, we can fix the problem of no heating in the microwave oven only when you have some basic knowledge about electrical/electronic devices. The reasons for no heating in a microwave oven is because if damaged magnetron or high voltage diode

Is it dangerous to repair a microwave? It causes danger when you don’t have enough knowledge about the microwave. And also it not a better option to repair when you are alone at home. An improper repair can lead to the shock and burn out parts.

How dangerous is a magnetron? A Magnetron is not safe even the power supply of it is in an off state. There are some traces of power inside the magnetron which can cause shock. And also the insulating material is also not safe to touch with bare hands as it is coated with the beryllium oxide which is a danger when inhaled.

Are magnetrons radioactive? No, the magnetron produces microwaves which come under nonionized are less harmful to the human. But continuous exposure can lead to some problems like burns, blood change…….etc.

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