Magnetron in microwave oven

This article is devoted to such a difficult issue as the independent repair of a microwave oven, namely, the diagnosis and replacement of a magnetron. Unfortunately, any, even the most reliable, technique sooner or later fails. A microwave oven is no exception to this rule. It is often possible to observe how a microwave oven slowly warms up or completely stops heating food, despite the fact that there are no visible signs of breakage. The activation is triggered, the fan is functioning, the plate rotates. Approximately 90% of the breakdowns occur on the magnetron in the microwave.

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How the microwave oven works

The food stored in the microwave is heated by the action of decimeter electromagnetic radiation on it.

Important! The frequency of electromagnetic waves used in household appliances is 2,450 MHz.

Radio waves of ultrahigh frequency, acting on the polar molecules of the product( this is mainly water), "align" them along the lines of force of the magnetic field. This leads to an increase in the temperature of the product. Waves of ultra-high frequency heat water, and it, in turn, warms up the whole product.

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What is a magnetron?

A magnetron is a device that generates radio waves of the required frequency. The magnetron device of the microwave oven is an electrovacuum diode:

1. Its main part is an anode of cylindrical shape made of copper, divided into 10 sectors with the same copper walls.
2. In the central part of the magnetron is located the cathode with the filament placed inside the filament. Its purpose is the emission of electrons.
3. In the end parts of the magnetron are placed magnets of the ring type of high power. They create inside the magnetron a magnetic field, which is necessary for generating ultrahigh-frequency radiation. The voltage applied to the anode is 4 thousand volts, and to the filament - 3 volts.
4. The energy is removed by a wire loop, which is connected to the cathode and output to the antenna-emitter. The microwave radiation comes from the antenna into the waveguide, and from it directly to the chamber of the furnace.

Important! During the work of the magnetron, a large amount of heat is released. The body of the device is placed in a plate radiator, which is blown by air from the built-in fan. Overheating of the magnetron in a microwave oven is fraught with its failure, so it is equipped with a protective device - thermal fuse.

We will deal with the purpose of these details in more detail.

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Thermal relay - what is it for?

We continue to deal with the question of what a microwave oven consists of. The thermostat or thermal fuse is designed to protect the magnetron from overheating, as well as to protect the grill, which is equipped with many models of microwave ovens. Thermal relays are designed for different temperature ratings.

Set the relay to a specific temperature value using a bimetallic plate.

Important! If the temperature threshold is exceeded, the plate bends and then the contacts are opened. The microwave turns off from the power. When the plate cools, its geometry is restored, and the contacts are closed again.

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Microwave oven fan

The fan is one of the most important parts of the microwave oven. Its functions are as follows:

• The blowing magnetron in a microwave oven, the fan prevents its overheating and ensures its normal functioning.
• All parts that enter the electronic circuit of the microwave oven require cooling.
• The fan cools the grill system.

Important! When cooking in the microwave, a large amount of heat and steam are released. Due to the slight overpressure created by the fan, water vapor and heated air escape through the special ventilation holes.

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System for blocking and protecting the microwave oven

The microwave radiation itself is so powerful that without certain precautions it can harm all living things. Therefore, the microwave oven is equipped with a shielded working chamber made of metal, which prevents the radiation coming out.

The glass from which the door is made is covered with a metal mesh that does not transmit radiation, which generates a magnetron into the microwave. In addition, it is important that the gap between the microwave door and the casing maintain its size. The oven is arranged in such a way that the electromagnetic wave has a zero value at the place where the door closes to the housing.

Important! To prevent the device from turning on when the door is open, there is a system of microswitches that control the position of the door. The number of such switches is not less than 3: to turn off the magnetron, turn on the backlight and "inform" the control unit about the position of the door.

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Control unit

This is a kind of "brain" of the device. It performs 2 tasks:

1. Disconnection of the device at the end of the time that has been set.
2. Maintains the set power value of the device.

Modern models of "microwaves" are equipped with such options:

• Built-in clock.
• Power level indicator.
• Ability to control power through the keyboard.
• A set of programs for cooking and defrosting products.
• A beep sound when the program is finished.

In addition, the control unit controls convection, upper and lower grills.

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Possible magnetron breakdowns

Magnetron testing is a pointless occupation without basic knowledge of its possible malfunctions.

Important! The mistake of many "craftsmen" trying to repair the microwave oven on their own is the complete removal of the pass-through transformer. Do this categorically forbidden, as it can provoke a malfunction of the transformer and the tanning of the device.

Here is an overview of the possible malfunctions of the magnetron in the microwave oven and their causes:

• Caps. It is designed to protect the vacuum tube. It is quite simple to replace it: a working cap from any magnetron will fit. The reason is simple: all caps have the same seating.
• Evacuation of the magnetron from overheating.
• Breakage of the filament. The cause of this malfunction is overheating of the magnetron. Switching on the oven with an empty chamber or loading it incorrectly can cause "self-tapping" of the thread. Diagnose the breakdown by measuring the resistance between the legs of the capacitor. Normally its value is from 5 to 7 ohms.
• Break through capacitor. This fault is diagnosed by a tester. Normally, the resistance between the capacitor contacts and the housing is infinitely large.

Important! For self-replacement of the capacitor, conventional solder is not suitable. It is necessary to use a refractory solder or a compact contact welding device.

The only magnetron failure, which can not be checked at home, is a vacuum violation. For this you need special equipment.

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Magnetron check

The cost of this device is quite significant, so you need to make sure that the cause of the malfunction is in it. So, how to check the magnetron in the microwave? The algorithm is as follows:

1. Disconnect the oven from the mains.
2. Open the cover and carefully inspect the inside of the device for visible malfunctions( burns, reflows and other malfunctions that are immediately visible).
3. In the next step, use such measuring devices - a tester or a multimeter. The test must begin with the main circuit board. You do not need to solder the parts, you can "ring up" and in the assembled state.
4. Note the condition of the thermal fuse.

Important! Of course, the ideal option is to check the magnetron on a special stand, but only a specialist can do it. At home, this is difficult.

If all elements of the power circuit are in good order, then the problem is in the magnetron. Have to buy a new one. You can install this spare part on the microwave without much difficulty.

It may be that the original is not on sale, so you have to think about buying an analog. Selecting an analog of the magnetron, you need to pay attention to the following points:

• Power.
• The location of the contacts connector.
• Mounting holes.

It is known that any disease is better to prevent than treat. Therefore, the proper operation of the microwave oven is the best prevention against possible malfunctions.