DIY repair microwave oven

We are 100% sure: stop understanding what is inside to carry out microwave repairs. Let's start with the simplest model, inside which there is a grill and a turntable, then it is not difficult to generalize the case to inverter models. We speak in a simple language, since we have found: on the Internet, discussing a topic, they say either irresponsible or use too narrowly specialized language, which is difficult to understand.

The device of the simplest

microwave oven. In the microwave oven, the electrical components are connected in series. Let's start with the power supply of the magnetron. Open the cover, you will see a huge transformer, next to it is a large( really large) capacitor, next to which a diode and a fuse huddle in a ceramic case( insulator).These things primarily attract the attention of a novice. This is the high voltage generation circuit( 3-5 kV) of the magnetron power supply. Do not put your hands in there, a screwdriver. We believe that the capacitor will slowly discharge, and if the plug is pulled out of the socket, an electric shock is unlikely. The principle of operation is as follows:

1. A voltage of 230 V is applied to the primary winding of the transformer. The coil is located below, wound with a copper core, sometimes seemingly bare. The metal is covered with transparent lacquer insulation. The coil is located under the secondary windings.
2. Secondary windings two. One literally represents a few turns of copper wire, carelessly wound next to the primary: heated cathode. Gives 6.3 V AC voltage, helping electrons to leave the surface. Above, in good, high-quality insulation, a high-voltage winding is located. Gives 2 kV, going to the output, the power of the magnetron.
3. The output is a capacitor, shunted by a diode. It turns out that the negative half-wave passes to the cathode, the positive charges the capacitance. In the next half-period, the electrode will already be under double voltage: removed from the transformer and discharge of the capacitor. The result is about 4 kV.Enough to start the generation.

Note: the output windings are connected in parallel on the magnetron, the cathode has two inputs. The anode is grounded separately.

Electrical layout is obtained:

1. A current of 6.3 V flows through the heating coil.
2. A potential of 4 kV is applied to the cathode, which is balanced by earth at the anode.

The heating coil and the cathode are electrically connected. The power of the magnetron is controlled by a timer, and in order to avoid sparks a starting relay is added to the circuit. We turn to the consideration of the front panel!

Front panel

On the front panel of the microwave oven is a mechanical programmer that sets the modes. Under the round handle lies a shaft, equipped( in our case) with two cam discs. The first is responsible for the power supply of the transformer that forms the power supply to the magnetron, the second is responsible for the quartz lamps of the grill. Cam mechanisms are controlled by two relay buttons:

• transistor key, blocking the power of the magnetron;
• quartz grill lamps.

If the cam is low, the button is released, the relay is in the normal position. When the projection is high, the relay button is pressed. It is easy to see that this way we will ensure a constant supply of voltage, and the power needs to be regulated. Let's talk below, but first back to the starting relay. The thing that removes the current load at the initial moment is connected in parallel with the input winding of the transformer. Power contacts are connected in series. Parallel to the relay are the capacitor and zener diode.

When there is a front that forms a spark, the capacitance represents a differential of zero resistance, the inductance of the transformer is separated by open contacts. Large current does not flow! The capacity begins to charge to a voltage limited by a zener diode. Discharges prevents diode included in the right direction. When the threshold value is exceeded, the relay is triggered, and a large current of the transformer and the magnetron supply is flowing. Due to the thoughtful progress, the timers of the microwave ovens with the protective relay almost do not burn. Now the programmer!

Equipped with gear, gear that regulates the clock. Depending on this, the intervals of operation and idle time of the magnetron change. The longer the rest, the less power is released. About the magnetron, we add: the introduction of the inverter control shifts the cycle control from the timer to the sensory temperature measurement circuit. The sensor evaluates the radiation spectrum of the food and decides how to operate the microwave. It is not the idle time( work) cycle that changes, but the pulse repetition rate. More often there are packages, more power. As a result, there is the possibility of flexible adjustment to the situation.

Protective Relays

Before talking about the grill, magnetron cooling fan, the backlight lamp of the working compartment and the table motor, I would like to mention the protective relays. Contactors provide a complete shutdown mechanisms when opening the door. Two tear the supply circuit( ground and phase), one necessarily controls the performance of the other:

1. The door is open, the relay buttons are depressed, the contacts, which are initially normally closed, are connected.
2. In this case, the power supply circuit must break twice.
3. But in the second relay the ground closes on the phase.
4. The first relay worked - nothing bad happens, the circuit is already broken.
5. The first relay is stuck, the fuse will knock out as the ground is shorted with the phase.

Interrupt the program by opening the doors. Perform the necessary operations. Close the compartment. The program will continue execution. Electromagnetic radiation instantly disappears, it is worth the protection relay to break the contacts.

Not a power fuse placed in the case and hanging under the magnetron, but located on the electronic board. Consider the curious features of protective relays. One( third) supplies the phase to the starting relay. Without this, the voltage supply to the magnetron is in principle impossible. The power fuse estimates the power consumption of the magnetron. If an abnormal situation occurs, the protective element burns, saving the generator from breakage. The described will happen if you turn on an empty microwave oven, or put a fork, spoon, metal object inside. The only bordering golden ring of the plate is capable of provoking an abnormal situation.

Service mechanisms

Usually in a microwave oven a series of units is connected in series. Now we are discussing secondary mechanisms: fan motors, tables, quartz grill lamps, a backlight bulb. This is done to reduce the number of wires. Design changes simplify microwave repair to the maximum. Result: the burnout of one element blocks the operation of the furnace. The magnetron is threshing, like the starting relay. The observed effect is a characteristic symptom of the cause, which lies in the auxiliary mechanism. Equivalent result if the third relay breaks, tearing the power circuit in normal condition( the door is open and the button is released).but if a relay is powered from it( as mentioned above), microwave oscillations will not be generated.

The given scheme is characteristic for microwave ovens, we believe, there will be other designs. Just take note of the artifacts of designers. The elements inside the microwave oven are powered with a voltage of 220 volts. There are no other special sources inside. Models stuffed with electronics, sharply knocked out of line. An inverter for operation requires a series of voltages.

I would like to note that in microwave ovens with hybrid modes, test almost 100% of the component parts of the product separately. Learn the design of the programmer. It is convenient to light the grill while the magnetron is off. Beginners wonder: how the grill power is regulated. We believe that the share of this component of the microwave oven costs energy that is not consumed by the magnetron. The microwave works longer, less remains to other components of the electric circuit.

Now let's say a few words about the occurrence of a fire inside a microwave oven: thunderbolts are beating. At the output of the waveguide, which transmits microwave energy to the compartment, there is a mica filter. Visually dense fabric, reminiscent of building insulation. The surface must be clean, dry. Otherwise, thunder and lightning will arise without difficulty. Fat contributes to insulation breakdown, as a result a discharge will occur inside. Have the stupidity of putting a plug in the compartment - the zipper will easily pierce the enamelled coating. There will be a black spot, in the worst the wall will burn through.

The main types of malfunctions are listed, the construction was told - we hope that the readers will play the feed.

Please note that microwave radiation is harmful to health. Therefore, repair of microwave ovens on a regular basis can not be called the best work.

Typical failures

In microwave ovens, the weakness of the owners is the weakness of the owners to properly use the product. Buyers are sure: the plates with a gold rim cannot be put inside, the dishes will break( detachment of the metal border), not a microwave. Everyday thinking is wrong. If you put a steel spoon inside, the likelihood of an electric arc is huge, if a jet of ionized air does not burn the magnetron( high-voltage fuse), it will leave indelible marks on the walls of the working compartment.

Mica gasket

We begin with a typical breakdown: breakdown of the casing at the mica gasket. The magnetron, through the pin, supplies energy to a waveguide, which is sensitive to the presence of contaminants inside. Grease stains burn, spark, interfere with the normal operation of the device. Therefore, the output of the waveguide cover with mica cloth. Soft flexible material, which is relatively inexpensive, is sold in large cuts, using scissors to form a piece of suitable shape. The principle of operation is based on the ability of mica to skip the frequency of 2.45 GHz heating of the microwave oven. Otherwise, the fabric gets very hot and burns out after a short work. Mica prevents the conductive walls from getting wet - it is important if the soup heats up inside: flying spatter causes irreparable damage to the cleanliness of the compartment. It has long been observed: water absorbs 2.45 GHz radiation, which promises troubles. If a liquid gets inside the waveguide, an emergency situation will arise immediately: the evaporation of molecules, changing the dielectric properties of the air environment, instantaneous breakdown, burnout of the high-voltage fuse, in the worst case of the magnetron, and other electronic stuffing.

Why the protective mica padding becomes unusable. The hostess prepares food, often among the ingredients of the formulation fat, oil, other substances. Substances do not boil, shoot dirty drops. The fat enters the mica tissue, a conduction bridge is formed. Apart from this, the natural mineral is a dielectric, it reliably isolates the waveguide from the body, the only drop of oil that has infiltrated the gasket is capable of blowing up this wall. An arc is formed instantaneously:

• between the walls of the waveguide and the mica cloth;
• between mica cloth and body.

Thunder and lightning are the first signs of an approaching microwave breakdown.

Proper grounding

If the device is not grounded, the situation is extremely dangerous. Enough to take the kitchen faucet with your right hand( substitute the palm with a stream of water), with the left - to accidentally touch the microwave oven to die. It is appropriate to recall: devices connected near water sources operate in tandem with a differential circuit breaker. Proper grounding is required. It is often not enough to zero the corresponding terminal. We review two pitfalls:

1. The ground resistance is negligible. Units, shares ohm.10 is already considered an invalid value. Therefore in a contour not wires, but tires( tapes) steel or other metal( alloy) of a large section are often used. It is clear that for the home network such conditions can not be achieved.
2. Differential circuit breaker works by fixing the leakage current. Measured output, input values, is the difference. If the leakage current goes to ground by zeroing, the magnitude of the differential is zero, even when the fuses are burned out by the overload, the magnetron is in addition.

Differential protection devices are often provided with fuse slots, but do not confuse them with safety features. Black humor masters repair TVs says:

• Fuse burns last, when it broke everything that could break.

And this means that a differential protection device cannot save human lives. It is required to ground the microwave oven correctly. Devices belong to electrical safety class I. The terminal is on the plug. Put the euro sockets connected correctly. And this is before grounding, why - they have already explained. We add that the ordinary socket or accident safety devices can not protect. In the case of the microwave oven, the chance of a favorable outcome of the accident is great.

High Voltage Fuse

As for what has been said, many had a question mark in their heads the size of a mountain, what is a high-voltage fuse. We explain! The microwave oven device includes two fuses( minimum):

1. The usual small transparent( glass), white( porcelain) cylinder on the electronic board. Ensures the safety of mounted, integrated elements. Low-voltage fuse, refers to the power supply circuit of the electronic board. It will burn if the capacitor breaks through, closes the resistor, located on the printed circuit.
2. The magnetron has its own power supply circuit, formed by a step-up transformer, diode, capacitor. The source supplies a cathode potential of several kilovolts. Items are easy to find. The capacitor looks monstrous: a can of a gram of a hundred steel, to which a diode is attached to the end, the second leg is soldered( screwed) to the body. Nearby you will notice a ceramic chest or another dielectric( often brown).Inside the Egyptian sarcophagus high voltage fuse. Protects the magnetron against overheating. If the current of the cathode becomes too large( it breaks through the mica gasket, or who inserts a spoon into the working compartment), the high-voltage fuse will blow out first. By the way, microwave oven repair technicians rarely complain about the power element. Therefore, it regularly performs duties( or, on the contrary, causes the failure of the magnetron).

You can not remove the high-voltage fuse from the electrical circuit, try to make an accessory with your own hands. Simply dangerous for the device, surrounding people. There will be a fire, someone will kill a current.

magnetron voltage shaping circuit Of course, we heard about microwave inverter in a microwave oven. Firstly, not very different in design from standard microwaves, and secondly, not everyone likes the flexible heating control mode, it is imperfect. Designers provide the option to disable, cook and use. To understand how a scientifically sounding microwave inverter works, consider the voltage-generating circuit of a magnetron: the

• microwave oven begins with a power transformer. The input winding is below secondary, assembled with copper wire with transparent lacquer insulation( heat transfer to the outside by infrared radiation) for better cooling. Above comes a pair of careless turns, forming a voltage of 6.3 volts of the cathode filament. Finally, the boost winding is located at the top, from where a potential of 2 kV( amplitude) is fed to the rectifier.

• The anode of the magnetron is planted on the neutral wire( not the body).The cathode is additionally heated to make it easier for electrons to leave the surface of the emitter. Negative voltage is used for power supply. Positively charged capacitor. The next half period of the cathode is under double voltage. The potential difference is formed by the difference between the secondary winding of the transformer and the capacitor. Forced measure to reduce the requirements for the power of the electrical circuit.
• A mains voltage of 230 V is applied to the primary winding of the transformer. In the case of inverter control, the duty cycle of the pulse sequence is modulated. As a result, the result is determined by the current value. The farther apart the pulses, the lower the level, the less power the magnetron gives to food.

Please note: the magnetron has two terminals, three wires start. Single feeds the heat, with a double - energizes the cathode, closes the circuit 6.3 V. The anode is connected separately, on the outskirts of an ingenious design. To supply voltage to the transformer in the electronic circuit has a relay. The measure protects the programmer( timer-controlled contacts) from sparking. In parallel, the relay is connected to a Zener diode, a capacitor, taking the impact of the front voltage connected. Then the anchor is triggered, power is supplied to the transformer. When the microwave oven is operating, clicks are heard periodically - the relay in question. The use of constructive details significantly increases the service life of the timer.

Timer( programmer)

The programmer is often formed by mechanical relays. The shaft of the stem contains a ring of different heights. Rotating the regulator, select the combination of states of the relay group. Depending on this microwave oven goes into the desired mode. It is clear that there is nothing to break here( and if it breaks, it is difficult to recover).If necessary, we check every relay; more often than not, similar steps are required. Refused contact grill - the lights go out. Let's say similar about the magnetron circuit.

Timer is more complicated. The shaft is covered with gears, each closing( opening) the contact. In the microwave oven, devoid of inverter control, the timer sets the frequency of switching on( off) the magnetron. The relay mentioned above blocks the arcing of timer contacts. When the inverter control in the compartment is a sensor infrared radiation, according to the sensor and is controlled by the duty cycle of the pulses( frequency).

What can break. Imitation of the clockwork inside the timer spring. Seeing a breakdown, replace the steel with a new one. The mechanism is durable, contacts rarely break. Described the main types of faults, of course, you need to start with a cord. Trivial breakdown, to blame in 20% of cases. Now readers are pretty aware of how to fix a microwave oven.

Breakdowns of microwave ovens

Many people are interested in how to check whether the stove gives the correct characteristics. In the literature it is written: the measurement method is in HBH 100 GOST 19308 - 80;A drawing and useful information are provided for the evaluation process. The beginning of the paragraph is written out from the book on the repair of microwave ovens, published in 2003.It is alarming that GOST is difficult to find in practice. The authors googled and found GOST R IEC 60705-2011.And the document is called “Household microwave ovens. Methods for measuring functional characteristics. That's from him and invited to continue to dance. The book is a little outdated. The text results in less and less used constructions of a microwave oven: radiation enters the working chamber from above. With strange modernity, the design course was supposed to create a uniform field in volume. Today, the waves are on the right, repairs are done differently.

Already hundreds of pages are written with the breakdown of capacitors, burnout of diodes, fuses. It seems that children of school age know that it is breaking. It is proposed to discuss not zamylennoe aspect - the microwave field, power, the distribution of the intensity vector, features and danger. In carrying out repairs, we often forget that the device is designed to help the family, and not to destroy humanity. Any Whirlpool can easily destroy the gene pool if you do not take appropriate security measures.

American scientists have long established that 2.4 GHz devices cannot be placed on their knees( see today's teenagers).Action negatively affects the reproductive function. On the wave of 1-2 GHz( approximately) cell phones and other gadgets work.

Distribution of the microwave field inside the microwave oven

Attention is paid to the distribution of the field inside the working chamber of the microwave oven, that's why! Electromagnetic propagation conditions are variable. If the structure of the field is constant within the waveguide, it strongly depends on the amount and type of food in the working chamber. Initially, the compartment is manufactured at a resonance frequency of 2.45 GHz;only food gets inside, the parameter floats, various parasitic effects appear. Not all are bad( negative), but places, sections of the compartment that do not warm up well, or warmed up, on the contrary, appear too overwhelming. Cheap microwaves provide rotating tables. The changeable panorama provides visibility of warming uniformity.

In expensive microwave ovens, the tray is stationary, the design of the chamber creates conditions for the field to be uniform and uniform. Readers already have a question mark in their head about the size of a house! If the light is shining, it is dark behind the cabinet, it is light under the chandelier. It is not difficult to realize the series of light with a shadow. Ilyich lamp emits a non-fixed frequency - band! As a result, the interference pattern eludes the eyes. Coherent waves can add up and subtract better. Same in frequency. Let physicists avoid blaming the review for too loose interpretation of the concept of coherence, a missing aspect of the phase of electromagnetic oscillation.

The wave goes into the working compartment, begins to re-reflect the walls in an incredible way. As a result, at an arbitrary point in space, two oscillations may occur in phase or antiphase. The picture is the opposite( light, shadow).

In the first case, we observe twice the power, the second - zero! If the human eye had a frequency of 2.45 GHz, the working chamber of the microwave oven would introduce itself to an individual spotted with specks, stripes of light and shadow. It is important to prevent the case of finding food in the zero field.

After repair, if work was carried out with a magnetron and a waveguide, the picture would be unpredictable. Knowing the Russian craftsmen, they are sure that a dozen microwave ovens will be found in the country, where the magnetron of the radar station is located. Indeed, what's the difference, on the microwave runway and in the microwave kitchen. In this case, it is recommended to check the parameters using the methods specified below, to assess the security of people operating the device. Special equipment at home is not available for sure, therefore it is proposed to simply substitute glasses of water on this side of the door and wait: is it warming up. Now the measurement technique according to GOST R IEC 60705-2011.

Checking the parameters of

The process begins with general measurements and settings:

1. The room temperature should be equal to 20 ± 5 ºС.
2. The temperature of the transformer, magnetron should not be above the environment by more than 5 ºС.Or, after working the microwave oven, wait 360 minutes. In the room, of course, where the measurements take place.
3. To measure the power of water is taken from the tap.
4. The dimensions of the microwave oven are determined according to the figure below. The useful radius is the distance from the center of rotation of the working table( or the center of the working chamber) to the nearest wall or door, and the useful height is measured from the surface of the rotating table to the nearest upper limit point. The net volume is expressed in liters, equal to the product of the useful height, depth, width.
5. If there are several ranges of network voltages, it is taken generally accepted in this country.

Measurements are carried out in a cylindrical bowl of borosilicate glass with a height of 90 millimeters with an outer diameter of 190 millimeters and a wall thickness of 3 millimeters. The material of the tank is characterized by a low coefficient of thermal expansion, which means that the water will retain its original shape. If anyone thinks that it is impossible to get a borosilicate glass, then this is a mistake. Glassware for microwave ovens is made of the specified material. They are inclined to think that the cook will find at home what is necessary for taking measurements.

The water temperature at the beginning is 10 ºС.Then electronic scales are taken, a bowl is placed on top, the readings are reset to zero. A liter of water weighs exactly a kilogram. The mass error taken for the experience of the fluid does not exceed 5 grams. If there are no electronic scales, then think of another way to get exactly 1 liter of water. Take a syringe and measure 5 milliliters.

The microwave oven is turned on( in the mode for which power is being measured), microwave radiation is working until the liquid heats up to 20 ± 2 ºС.Wait with a closed chamber for 1 minute and record the final temperature of the water in the bowl. Please note: before measuring the liquid is stirred. Subtle moment. You can not do the technological operation with an iron spoon. Suitable, for example, plastic ladle from the multicooker. So that the liquid does not lose some heat. Steel has a high thermal conductivity, which is why the room seems to be more cold than plastic objects. Although the temperature difference is zero. The power of the microwave oven in the selected mode is according to the formula:

mw, mc is the mass of water, the container;That, T1, T2 - ambient temperature, water at the beginning and end of measurements, respectively;t is the time for which the required temperature is reached. The resulting value is rounded to 50 W according to the general rules of mathematics. Measure the power of the microwave oven, hardworking readers expect a big surprise. Already said that it would be nice to put the bowl near the door outside, and inside another one. Using a similar technique, evaluate the quality of the protective mesh. Break, the whirlwinds of microwave energy will burst into the kitchen and will fry the food that comes along. For those who do not know, we report that working with antennas, as well as transmitting and receiving devices, is considered a harmful factor. Therefore, getting a specific job undergoes additional examinations, top pay for harm. Has the cook family already passed a medical examination?

Take the trouble to evaluate the microwave leakage from the camera. The reason for the poor quality of insulation lies in the lack of grounding. Most microwave ovens belong to electrical safety class I. The plug is equipped with a ground lobe. Contact hanging in the air, the normal operation of the microwave breaks. Try grounding as recommended by the standards, re-evaluate leaks.

Ideally, if you put a cell phone into the switched off microwave oven( the plug of which is in a grounded outlet) and call it, then the call should not go through. This means that the metal mesh on the door truly copes with its responsibilities by 100%.For hokhmachi add that outside the microwave signal should pass confidently, responding with a cheerful call to the request of communication towers.

This is interesting! Once, a painted-up girl ran in to the authors and said that she was distributing goods for advertising the store for free. She said that sturgeon never get sick and praised the product very much. Then, for such a gift, we showed her the focus: we took an EMP indicator screwdriver and cut off the ground lobe. Even with the microwave turned off, the instrument was buzzing like a cut( aiming from the primary winding of the transformer).

Trying to repair a microwave, remember safety. Usually women and children are in the kitchen. Why is there a harm factor? It would also be nice to know the microwave device thoroughly. According to our memoirs, if the screen is not grounded, then it dampens( reflects) only half of the radiation. The rest goes. Therefore, you can safely catch half of the measured power in the kitchen, if the installation of the microwave oven is carried out incorrectly. In conclusion, we wanted to bring a couple of pictures from the standard. Everyone at their leisure can watch, read the text, measure the values. In this case, we will already be talking more about the distribution of the field( this was written at the beginning).Well, for example, if you need to heat a beer, then it becomes clear where to put it! And in no case do not warm the milk in baby bottles in microwaves. The dangers of such an approach have already been reviewed( as corrupt officials would say).Do not forget to watch the video instructions in our article!