- The device of microwave ovens
- Replacing the mica plate
- Features of high-voltage fuse
- The principle of operation of the safety relay
To repair the microwave, you must have a general idea of how it works. Repair microwave oven begins with the removal of the top cover. Before that, you should take care of the device being completely disconnected from the power supply network, and only then proceed to fix the damage yourself.
When these actions are successfully completed, a transformer with two fuses will open for access: one is located directly on the part itself, it is low-melting, the second is located nearby on the housing of the microwave oven, made of ceramics. Also next to the transformer is a doubler unit, consisting of a thick capacitor and a diode. The whole set of these elements is the power supply circuit of the magnetron of the microwave oven.
Caution! Do not immediately touch the condenser immediately after removing the top cover plate. This element is able to hold the voltage for a long time, which can easily lead to electrical shock. When repairing a microwave oven with your own hands, this factor should be taken into account.
The device of microwave ovens
The feature of microwave ovens is that all the details are connected in series. First, pay attention to the above magnetron and its power supply circuit. After removing the protective case, a transformer with a large capacitor located nearby becomes available. There will also be located ceramic, fusible fuses, diode. According to this high voltage circuit, the magnetron operates. Under no circumstances should you get there with your hands, tools. After a complete blackout, the capacitor will lose residual voltage, the probability of electrical shock will decrease.
Circuit operation principle:
- The primary winding of the micro transformer assumes 220V.As a rule, its location is below. You can recognize it by the turns of copper wire, which will be bare in appearance. However, it is not. It is covered with a transparent insulating film. The location of this coil is under the secondary winding.
- The microwave oven has two secondary windings. On one of them, usually in a not neat form, several windings of a simple wire are wound. This heats the cathode. There is an alternating voltage of only 6.2V, so that the electrons can detach from the surface. But where there is good insulation, there is a high voltage winding. About two kV directed to the exit.
- A diode-shrouded capacitor is located at the output of the circuit. The action of the negative half-wave falls on the cathode, the capacity of the positive half-wave is charged. Next, the electrode is subjected to double the voltage, which is removed from the capacitor and micro-transformer. As a result, approximately 3.5-4kV are generated. This power is enough to start the generation process.
You should be extremely careful, the output winding is always parallelized by a magnetron, which has two ways of output. But the grounding of the anode is performed separately.
Thus, this is what happens:
- heating coil has 6.3V;
- on the cathode is up to 4.2kV, grounded by the anode.
All microwave ovens have an electrical connection for the cathode, the heating coil. Each microwave oven is equipped with a timer that controls magnetron power. The use of a start relay is used to avoid the occurrence of a spark. Next you should pay attention to the front panel.
Read also: How to repair a convection oven with your own hands
Replacing a mica plate
The most likely damage occurs in the area of the mica plate. Energy is supplied to the waveguide from the magnetron rod. The latter has a high sensitivity to the presence of various food residues. All these contaminants begin to ignite, giving off sparks, thereby disrupting the stable operation of microwave ovens. To avoid unforeseen situations, the developers decided to close the waveguide with a mica plate. It has soft, flexible properties, relatively affordable pricing. To fix such a break with their own hands will not be difficult. You can buy material of any size, cut the corresponding segment. The peculiarity of the mica plate is that it transmits the frequency level of 2.45 GHz without obstacles. It is at this frequency that the microwave oven functions.
Also, mica plates do not get wet. This is a very important factor if the liquid inside the microwave is heated. After all, water very quickly absorbs the radiating frequency of 2.45 GHz, there is a danger of serious damage. If the water reaches the waveguide, a big accident is created, which will not be easy to repair with your own hands. High voltage fuse instantly burns out. If everything gets worse, the magnetron itself burns, the other electronics, which is filled with a microwave oven.
What factors affect the destruction of the mica plate? Most heated foods contain a variety of fats, oils, and other similar ingredients. They differ in that instead of the usual boiling, they shoot fatty drops. As soon as such a drop hit the mica plate, a small wire bridge is created. An electric arc is formed: from the waveguide to the mica plate, then from it to the body of the microwave oven. As soon as there are claps and sparks that are uncharacteristic for the operation of the furnaces, this is a sure sign that the furnace will soon require repair.
Read also: DIY repair of multicookers
Features of high-voltage fuse
Everyone who tried to fix the microwave with their own hands wondered about the high-voltage fuse. The mechanism of microwave ovens of this kind launches at least two fuses:
- If you look at the electronic board of the microwave, this detail appears as a white or transparent cylinder of a small size. Its task is to protect the integrated, mounted elements of microwave ovens. Also this small cylinder is part of the power supply circuit. It burns out in case of a capacitor breakage, a resistor circuit.
- The power supply circuit of the magnetron includes a diode, a transformer, a capacitor. Through them about two or three kilovolts approach the cathode. Discovering these details is not difficult. The appearance of the capacitor is difficult to confuse with anything. This is a huge detail in the form of a jar weighing up to one hundred grams. One diode leg is attached to it, the other is attached to the body. Nearby is also a small barrel, often ceramic, painted brown. It is this barrel contains inside a high-voltage fuse. His task is to prevent the magnetron from overheating. When a mica plate breaks through or a metal spoon is put in the microwave oven, a high-voltage fuse blows immediately.
It is better not to try to assemble the high-voltage fuse with your own hands or remove it from the electronic board. This practice is extremely dangerous for people. The microwave oven may stop working, there is a high probability of fire and electric shock.
The principle of operation of the safety relay
Before you start talking about repairing a fan, cooling the magnetron, grills or a lighting lamp in the microwave oven chamber, you should also pay attention to the protective relay. Their task is to turn off all running systems while the camera door is in the open position. Two relays typically break the power supply circuit. And one relay will be controlled by the functional ability of the second. The operation is as follows:
- In the event that the door of the furnace is open, the relay trigger is released.
- In this operation, the power supply circuit has two break points.
- The second relay closes the earth in phase.
- When the first relay is triggered, nothing bad will happen, since the power supply circuit is in the open position.
- When the first relay sticks, a fuse is knocked out. This is due to the fact that the earth is shorted phase.
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A fuse means not the one on top of the magnetron or inside the case, but on the board. To fix the microwave with your own hands, you should check the operation of the protective relay. Without this functionality, power supply to the magnetron is practically impossible. The task of the power fuse is to take into account the movement of current in the magnetron. In the event of a dangerous situation, the protective element burns out and the generator breaks down. A similar situation occurs when the microwave oven is idle or there is a metal thing in its chamber.