Repair of microwave ovens

The microwave oven is a modern assistant for many families. When it breaks down, all members dream of quickly returning it to the working form. Of course, if the microwave oven is warranted, then you just need to pack up and take it to a service center. But if the warranty period has long passed, then when referring to the master will have to spend. However, not every failure requires the intervention of a specialist, quite often the repair of microwave ovens is under the power of the owners of equipment themselves.

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Just about the complex device

In appearance, some users may get the idea that a microwave oven is a highly complex device, but it's far from the case.

The main parts of the microwave:

• food heating chamber;
• waveguide;
• magnetron;
• power supply
• programmer;
• high voltage relay.

Important! Such a rapid heating of food in the device is ensured by the fact that it uses doubled voltage. Therefore, microwave ovens should only be repaired:

• with appliances completely disconnected from the power supply;
• after forced discharge of the capacitor.

And even in this case, there may be a residual charge in the circuit.

Principle of operation:

• When the equipment is switched on, electricity is supplied to the primary winding of the transformer. As a rule, it is located at the bottom and consists of a copper wire, which because of the transparent insulation many consider bare.
• Along with this, the voltage is also applied to two secondary windings of the transformer. One of them is responsible for heating the cathode and is an ordinary wire that is twisted into several turns. In this winding only 6.3 V. And here the second winding is high-voltage, which is in good isolation, and the voltage in it is about 2 kV.
• At the output there is a capacitor, in parallel to it is connected a diode. As a result, about 4 kV are removed from the transformer, which is enough to start the generation.
• Further pulses are transmitted to the magnetron, which directly and delivers the working energy to the food heating chamber.
• To control the duration of heating, a timer is used on the gears.

Important! Since the microwave oven is an increased source of danger, it has an entire safety system, which includes a relay to protect against voltage drop and shutdown when the door is opened.

Programmer

The microwave oven is designed simply enough, therefore all processes are controlled by a mechanical programmer. Similar regulators, only a little more complicated, can be found in washing machines.

There are two cam discs inside the programmer:

• one of them supplies voltage to the transistor;
• the second - is responsible for the supply of quartz grill lamps.

It's easy to understand that in this way only direct voltage supply in the microwave oven is regulated. And how to manage the power?

• Microwave power is regulated by alternating periods of work and rest. The smaller the simple, the more power is allocated, and vice versa.
• Inside the programmer is a timer, which consists of a gear or gear transmission - analogous to the clock mechanism.
• After a certain period of time, the programmer closes or opens the circuit, thereby turning the transformer on or off, and through it the magnetron.
• To avoid sparks during connection or disconnection of contacts, the wiring diagram in front of the transformer is supplemented with a control relay. It waits until the voltage on the control gate rises to the required value, and only then starts the current in the circuit.

Important! The relay takes over the entire impact and prevents the appearance of a spark. The reliability of the microwave oven largely depends on the quality of its performance.

By this principle, classical microwave ovens operate. In modern models, inverter control is often used - instead of a timer, the magnetron is powered by a temperature measurement sensor. He decides how to operate the microwave oven, based on the evaluation of the spectrum of food radiation. In this case, the power is regulated no longer by idle time and by operation, but by creating pulses with the required parameters.

Safety relays

Speaking about the structure of the microwave oven, we can not fail to mention the protective mechanisms that ensure the safety of the use of equipment. Since the microwave oven is a high-risk device, if the door is opened during operation or just in standby mode, a complete shutdown of all processes provides several relays simultaneously. Often, two of them break the circuit in phase and ground, with one relay "podstrahovyvaet" the other.

Here's how the protective microswitches work:

1. With the door closed, the circuit is closed, the relay buttons are released.
2. When opening, the chain must be torn twice.
3. If the first relay does not work, the correct operation of the device is provided by the second relay, which also disconnects the contacts by that time.
4. In the event that both relays are stuck, the fuse will be knocked out.

Important! When carrying out repairs to the microwave oven with your own hands, be aware that this fuse is on the electronic board. Do not confuse it with a power fuse, which is built into the case and is under the magnetron.

With a small number of relays, the microwave oven requires constant monitoring, especially if the house has children. Such a technique does not have a protective mechanism from the inclusion of an empty chamber or in the presence of metal objects. In this case, the microwave can produce excessive power, which can lead not only to breakage, but even to the fire or explosion of the device.

Important! Here all the hope is only on the power fuse, which estimates the energy consumption of the magnetron. In case of excess of norms it should simply burn down, to open a chain and to save the generator.

Additional mechanisms of the microwave oven

Microwave oven service mechanisms ensure the convenience of using the equipment, but do not affect the operation of the device in any way. These include:

• fan motors;
• dish table motor;
• quartz grill lamp;
• lighting lamp.

As a rule, all these secondary mechanisms are connected in a series circuit, so when one fails, the rest do not work either. Repair of conventional microwave ovens in this case is simple. However, modern devices with electronic control and inverter control will have to tinker.

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Safety precautions

Before proceeding with the self-repair of the microwave oven, be sure to read the basic rules of this procedure and use the device:

1. Do not, under any circumstances, switch on the magnetron that was removed from its original position. Life threatening!
2. Do not start the microwave oven if the fan is defective. This can cause a malfunction of the magnetron.
3. Never start the microwave oven with:
   1. open the door;
   2. waveguide failure;
   3. camera damage.
4. Microwave repair can be carried out only after disconnecting from the mains and removing the accumulated voltage.
5. All parts can be replaced only by analogous, and preferably - by identical, original spare parts.
6. When testing, you can not turn on the device with an empty camera. At a minimum, put a non-metallic bowl of water.

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Basic malfunctions of the microwave oven

Often the cause of malfunction of certain microwave oven mechanisms is improper operation or transportation of the device. Most of the factory defects show themselves at the initial stages, so repairs are for the warranty period and will be free. Consider the main symptoms of breakdowns and how to eliminate them.

Microwave does not give any "signs of life"

If the microwave oven does not react in any way to opening the door and to the control knobs, the reasons should be diagnosed and the cause should be identified:

1. Make sure that the mains filter card receives voltage. To do this, you first need to inspect the power cord for integrity, and then check with a multimeter. All three wires that go from the outlet to the terminal must be called. Also, the ground terminal of the outlet must be called on the housing of the microwave oven.
2. If the power cord is OK, the mains fuse should be inspected. Most often it is located on the power filter board. In the event of a malfunction of the mains fuse, repairing the microwave oven is simple enough - it simply needs to be replaced with an identical one at the nominal value.

Important! It should be understood that the fuse itself does not burn - there must be a reason.

Inspect visually all the mechanisms of the microwave oven. The presence of streaks, dark spots, holes from breakdowns - all this indicates a malfunction. The smell can also help in your search: perhaps you will smell burning insulation or transformer oil - this will help to quickly identify a malfunction.

Service mechanisms work, but the microwave does not heat

If the bulb burns when the door is opened, the table rotates at start-up, but the food does not warm, then this may be a sign of a malfunction of the main-machine circuit or magnetron.

First steps to diagnose the

But before you start checking these items, you should first inspect the camera and its parts:

1. The inner walls of the microwave oven must not have any holes burned, worn out enamel or other defects.
2. In the chamber on the left side there is a rectangular window-plate from the radio-transparent dielectric. It must be removed and considered.
3. If the window is contaminated with food residues, wipe it with alcohol.
4. If the plate has darkening or uncharacteristic holes, then:
   1. it must be replaced;
   2. is evidence of improper use of the microwave oven, for example, a metal object was placed in the camera or included without loading.

Then you should start studying the high-voltage circuit. Special attention should be given to such elements:

• power fuse( diode);
• transformer;
• capacitor;
• diode.

If before that there were metal or other unsuitable items in the camera, the safety diode most likely triggered. In this case, the entire repair of the microwave oven with its own hands is reduced to the replacement of the damaged element. It is located near the condenser and is enclosed in a box of ceramics or other dielectric.

Important! Such a diode can only be replaced with a similar one, equal in nominal value to the "native" one. In no case can you make a power fuse yourself or exclude it from the circuit at all - it can lead to a fire in the microwave or injury to the user's current.

Condenser, transformer

Also a reason for switching on a protective diode may be a breakdown in a capacitor or diode. Check these items before testing the performance of the microwave oven.

To exclude the breakdown of the transformer, you need to call it with a multimeter. To do this, disconnect it from the load and the primary winding - just remove the corresponding terminals by pliers.

Important! The following resistance is considered to be normal:

• of the primary winding - 1.5 Ohm;
• high-voltage( secondary) - 110-120 Ohm;
• of the secondary winding - 0,1 Ohm.

If at least one wiring is not called, the transformer should be replaced.

To test the capacitor, you can use a household low-power lamp, the desired parameters are 15 watts per 220 V:

1. Disconnect the condenser. Outwardly it looks like a small tin can, one end of which is attached to a diode, and the other to a casing.
2. Connect the capacitor in series to the luminaire.
3. Then connect the entire circuit to the outlet.
4. If the light is half-hearted, then the capacitor is OK.
5. If the lamp is lit brightly or not at all, the element is defective and should be replaced.

Important! By the same scheme as the capacitor is tested and the diode. If this element is out of order, then during the repair of the microwave it should be remembered that the new diode should be connected to the circuit in the same way as the previous one. If you mix up the ends, the technique will not work.

Magnetron

Another reason that a microwave oven does not heat, may be the failure of its "heart" - the magnetron. To check it, you should:

1. Disconnect the magnetron terminals from the transformer.
2. If the terminals are pierced to the housing, then a breakthrough of the pass-through capacitors in the filter has occurred. You can replace the filters or the entire capacitor assembly.
3. If the terminals are OK, remove the magnetron from its nominal position and evaluate the condition of the antenna cap. If it has damage or burnt spots, a replacement is necessary.

Important! When repairing microwave ovens, if you need to replace the antenna cap, install only the exact same size. There are no other options here!

1. Also inspect the magnetron insulator.
2. If the antenna or magnetron housing is broken, its replacement is clearly needed. However, this is often not economically viable.

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Malfunctions of the lockout system and the

control unit If all the basic elements of the microwave oven have been tested, but the device does not work, there may be a reason for the malfunction of the door mechanism or the control unit. Such breakages are quite rare, but still they happen.

Testing the

lock system First, you need to check the lock and the tightness of the door:

1. Take a sheet of paper and insert it between the case and the door.
2. Close the door.
3. The paper must be clamped very tightly. In order to pull it out, you will need to apply a lot of force.
4. Check the entire perimeter of the door.
5. If in some places the paper is not sufficiently clamped, adjustment is necessary. It is carried out both from the side of the hinges, and from the side of the castle.

Then you need to test the microswitches. To do this they call the tester with the door closed and open. If at least one of them is faulty, then everything should be replaced.

Important! Since the wear of these elements is approximately the same, when replacing one in the near future you will have to change gradually and others.

Control unit malfunction

Many control cards have a separate fuse. If it is burned, this could just be the cause of the inoperability of your microwave oven:

1. Remove the board and inspect it.
2. If the fuse blows, it must be replaced with a new one.
3. Damage to tracks, the presence of fumes or bloating of condensers - all this indicates problems in the control unit. In some cases, something can be soldered, and sometimes a complete replacement is required. Since each motherboard has its own individual scheme, there is no sense to consider possible microwave repair options in the article.
4. If it is suspected that there is a fault in the power transformer, it must first be thrown out of the circuit and only then it will turn out to ring.

In conclusion, I want to say that most of the malfunctioning of microwave ovens is a consequence of misuse. As you can see, despite the fact that such a technique has a fairly simple device, repairing a microwave with your own hands requires some knowledge of electrical engineering and compliance with safety rules.