Microwave oven repair: is it worth it yourself, oven design, typical cases. Chapter five. Multicavity magnetrons What does a magnetron consist of?

Service maintenance of household microwave ovens (microwaves) is a vivid example of the ideology of the consumer society in action: the warranty period is assigned a relatively long time, but after its expiration, repairs often turn out to be more expensive than purchasing a new product. The impact on the environment and the economy of the fact that industry “threshes for the landfill” is fully understood by a narrow circle of well-trained experts, candidates for which are carefully filtered. Therefore, for the average citizen the question: how to repair a microwave oven with your own hands is obviously important economically, because... technically quite feasible at home.

However, the microwave oven is an equally clear illustration of another consumer-ideological problem, when the qualities of a product that contribute to the demand for it are emphasized in every possible way, truly useful, but not so spectacular, are mentioned in passing, and the potential danger is obscured by streamlined expressions. The last one from the microwave is quite large and treacherous, so Repairing a microwave oven must be done with a clear understanding of what can be done and how, what cannot be done, what should be avoided and feared. The purpose of this publication is precisely to give readers such an idea.

What is visible from the outside

Let’s take a closer look at our “micro” again, see fig. We immediately draw your attention to the fact that the latches have different configurations: they are not just locks, but also parts of the electromechanical locking system (EMB, see below). We also remember the output window of the waveguide, which is usually not noticeable. Repair of a microwave oven will most often be associated with the units marked with letters; For the programmer and power regulator, their external controls are marked. In “digital” microwave ovens with full touch control, the electromechanical programmer and power regulator are replaced by electronic ones. Repairing them requires special knowledge, but everything else in digital devices works the same way.

Note: The programmer is often called a timer, even in proprietary manuals. In fact, the timer is only one of the functional units of the programmer.

What is inside

If you remove the outer casing of the microwave, a picture of its structure is shown in more detail, see fig. In newer furnaces (on the right in the figure), components critical for reliability (high-voltage unit, EMB and programmer) are covered with protective covers and a high-voltage fuse is necessarily added; The first microwaves didn't have it.

On the 2nd prev. rice. The backlight lamps, grill and table rotation mechanism are not visible. This is no accident: getting to them without removing the working chamber or without completely disassembling the stove is possible in most modern models (yellow arrow on the right in the figure), and in some old ones. This complicates independent repairs, because in order to fix a generally simple problem, you most often have to remove the magnetron, which is bad, see below.

What does it mean?

All this filling is needed to immediately heat up the entire load of food products with ultra-high frequency (microwave) radiation. It is produced by a powerful compact microwave generator - a magnetron. What is a magnetron, how it works and how it works, see video:

Video: about the structure of a microwave oven magnetron

Microwaves penetrate into partially electrically conductive media to a depth of approx. equal to its wavelength and is absorbed by the medium, releasing thermal energy. The microwave wavelength of the standard frequency for microwaves, 2.45 GHz (sometimes 2.85 GHz), ensures complete microwave absorption by the product load. This is where the most useful property of microwave heating manifests itself: thanks to heating in the mass, the temperature of the product does not rise to values at which hydrolysis of fats begins, producing toxins and carcinogens. This is especially important for heating food, because if it is done on a flame or from a heating element, then the hydrolysis of the fats remaining in the food continues, and its existing products decompose deeper, into even more harmful substances.

Note: Microwaves almost do not penetrate into metals, because their conductivity is caused not by individual charge carriers, but by the so-called. degenerate electron gas. It also gives a metallic shine and malleability. Therefore, it is strictly forbidden to place metal objects in the microwave chamber - all the microwave energy will concentrate on their surface, causing excessive heating, arc discharges, etc., after which all that remains is to throw away the stove. Unless the magnetron power transformer is suitable for .

However, for the same reason, the physiological effect of microwaves on living organisms is strong, harmful and may not be noticeable at first. This requires the use of special safety measures during the design, production, ongoing operation and repair of microwave ovens, see below.

The functional diagram of a microwave oven is shown in Fig. The configuration of the waveguide and microwave flow are shown conventionally; a circuit more or less corresponding to the real one is given in the inset at the bottom right.

1a – mains current pulses with a voltage of 220 V. The radiation power of the magnetron is not smoothly adjustable, so to control it it is necessary to use pulse width modulation (PWM, see below). 4a and 5a – internal control signals. 6a – high constant supply voltage of the cathode (emitter) of the magnetron – 4000V; 6b – power supply to the magnetron filament circuit 6.3V 50/60Hz.

Modern microwave ovens are built according to the so-called. circuit with a shortened microwave path, increasing the efficiency of the furnace. In this case, the chamber is tuned to resonance, which is why, firstly, without a microwave energy-absorbing load, the stove will burn itself with its radiation. Which is what is indicated and the instructions for it.

Secondly, the magnetron produces coherent radiation, therefore, due to the interference of reflected waves in the chamber, the product is illuminated unevenly by the microwave. To ensure that the load is baked properly, it is placed on a turntable. As a consequence, a malfunction of its mechanism can lead to more serious problems, see below. Just like a malfunction of the internal convection system in the chamber, which modern microwave ovens are equipped with for completely uniform heating of food.

Safety regulations

Already according to the functional diagram, a household microwave oven can be divided into components and modules that require compliance with the corresponding requirements during repair. safety precautions:

External 220V power supply circuits and the control module are general safety measures for class I electrical installations in terms of the degree of danger created by electric shock.
Power supply (PS or power supply unit) of the magnetron - safety measures for electrical installations over 1000V, capable of delivering power of more than 60W for more than 1 s in the output short circuit (SC) mode.
Magnetron and microwave path - special safety measures for high-power microwave installations.

I class

Look at the back of your microwave. You'll see a contact pad down there with a metal threaded pin and a nut on it - unless someone has already screwed it on. This means that the microwave oven belongs to electrical installations of hazard class I, which must be connected to a separate protective grounding circuit with a current flow resistance of up to 4 Ohms tightly, i.e. permanent connection. A detachable connection to a grounding conductor through a Euro socket is not considered to be tightly grounded. Such requirements for a microwave oven are determined by the coincidence in it, formally speaking, of more than 2 hazard factors:

The presence of electrical voltage over 1000V;
Availability of a microwave radiation source;
The air temperature is above 30 degrees Celsius, its relative humidity is more than 85% and the presence of volatile substances in the air in the form of evaporation from heated food.

About grounding

In countries with a metal-efficient power supply system with a solidly grounded neutral TN-C, incl. In the Russian Federation, it is technically not possible to provide all residential buildings with protective grounding circuits, and a global solution to this problem is not expected in the foreseeable future. Safety guidelines take the reader from paragraph to paragraph and from point to point, without providing general guidance suitable for each specific case. The general meaning: saving drowning people is the work of the drowning people themselves. Look for every opportunity to arrange a protective grounding circuit, at least an individual one of a simplified design. If there is none - regularly check the microwave for the quality of shielding and the microwave “siphon”, see below. Although formally this would be a gross violation of the safety rules and regulations and it would be useless to sue even a helpless homeless person for damage caused by a microwave oven. True, there is no need to fear a fine for violation; Due to the widespread use of microwaves, this is no longer legally feasible.

High voltage

The degree of influence of electric current on a person depends on the state of his body, the strength of the current, the time of its exposure and the amount of electrical energy released in the body. Therefore, for example, a TV with a picture tube and a stun gun (up to 25 kV at the 3rd anode of the picture tube and 35 kV at the output, respectively) do not belong to class I: the high-voltage rectifier of the first is not capable of producing a dangerous current even in normal operation, and the portion the energy at the output of the second is precisely dosed. Although, if you put your hand into the line scan of the TV, the sensations will be disgusting. The defining parameters of the impact of electric current on a person are as follows:

The electrical resistance of a healthy body is 100 kOhm; in a state of intoxication, sick, steamed, tired - 1 kOhm.
The dangerous current from the point of view of possible long-term consequences is 1 mA.
The non-releasing current causing muscle cramps is 10 mA.
Instantly (within 1s) killing current – 100 mA.
The maximum permissible energy release in the body for 1 s is 60 J, i.e. power – 60 W.

This follows the division of electrical installations into 2 broad categories: up to 1000V and over 1000V. The former may still be safe; the latter are certainly dangerous. By the way, a TV and a stun gun are also dangerous, but their degree of danger is not the highest, because due to one factor.

One more point must be taken into account: a person’s individual susceptibility to electric current varies within very wide limits. This is especially true for the permissible discharge power; frankly speaking, it is “lightweight”. Taken on the basis that a person under normal conditions excretes approx. 60 W of heat, but there is no reliable physiological justification. 60-watt pulses are sometimes used to treat severe and dangerous mental patients, but it is better to avoid pulsed current discharges through yourself altogether, because They are the ones that most often produce long-term consequences. The microwave is especially dangerous in this regard, because... power is supplied to the magnetron in pulses. Therefore, before repairing it, you must strictly perform the following preparatory procedures:

Completely disconnect from the power supply by removing the plug from the socket;
Wait for the standard time for discharging high-voltage capacitors through a standard resistor - 20 minutes;
Disconnect the grounding conductor (if any);
Wait 3 more discharge times, i.e. 1 hour;
Only now can you remove the outer casing and start working;
All work should be carried out only with the microwave oven completely turned off (with the plug removed from the socket and the ground wire disconnected);
In the process of self-repair - no trial starts! If replacing the suspicious element does not help, we leave everything as is and contact a certified specialist. Or we are looking for funds for a new stove, having found out the cost of repairs.

Note: perform a forced discharge of high-voltage capacitors by any means (for example, shorting the terminals with a screwdriver) outside a special laboratory extremely dangerous! Remember - the energy accumulated in a capacitor is proportional to the square of the voltage across it!

High voltage is especially dangerous for electrical installations if handled incorrectly. For example, grasp a high-voltage wire with your fingers. Completely safe, de-energized and discharged. When working under the influence of an electric field, grease diffuses quite quickly (as they say now, it migrates) into the insulation, which will soon lead to its breakdown. Therefore, when working with high-voltage components, you need to wear clean latex gloves; if possible, handle parts only with a tool, and upon completion of work, wipe with 96% technical ethyl alcohol. Not a medical distillation! Technical alcohol leaves small streaks of salts, because... Sulfation is used in its production. When the part is completely dry, drips are removed with a clean, dry, washed flannel rag or, better yet, a microfiber cloth for cleaning glasses.

Microwave

The effect of microwaves on the human body is in many ways similar to that of penetrating radiation:

A single exposure to a large dose can immediately cause irreversible health problems, of which the loss of reproductive abilities is not the most severe.
There is a certain threshold value of microwave energy flux density (EFD), below which its effect on the body does not affect the body either immediately or in the long term.
Within the limits of the PES value from the threshold of susceptibility to a noticeable physiological effect, microwave irradiation has a cumulative effect - it may be completely imperceptible at first, but later it will manifest itself in the most dangerous way. Typical after-effects are genomic disruption, leukemia and skin cancer.

Microwave radiation also differs from ionizing radiation in a bad way: it easily leaks out of its allocated volume through cracks and along electrical conductors protruding outward. Experts say that microwave siphons very well. Therefore, it is better not to undertake the repair of the microwave path of a microwave oven, from the power input to the magnetron to the output window of the waveguide, without deep special knowledge and equipment: if, according to the test results (see below), it does not siphon immediately after the repair, it will siphon later.

The matter is further complicated by the fact that the limits of individual susceptibility to microwave radiation are even wider than to electric current. The threshold of perception is so blurred that, for example, in the USA they accepted the monstrous value of PES as the maximum permissible value - 1 (W*s)/sq. m. A person directly feels such radiation and must immediately leave the danger zone, because Microwave PPE of this magnitude causes plasmolysis of body cells. Long-term consequences - you have health insurance at the expense of the company. Is medicine powerless in your case? Sorry, you were immediately warned about the possible consequences.

In the USSR they went to the other extreme, accepting the permissible PES a million times less - 1 (μW*s)/sq. m; this is approximately 5 times lower than the natural microwave background in mid-latitude areas with infrequent and mild thunderstorms. Everything would be fine, but it turned out to be technically impossible to provide shielding to the required degree for microwave installations. Although, by the way, the frequency of occupational diseases among personnel working with microwaves in the USSR was approximately three times lower than in America.

A new or immediately after repair microwave oven must be checked, firstly, for the quality of shielding; secondly, whether the microwave is siphoning from it during operation. Exactly in this order: if the shielding is good, then the microwave dose that you receive within an hour at a distance of more than 1 m from the stove will not exceed one time permissible for the most sensitive person.

Shielding

To check the microwave for shielding quality, firstly, you need to completely de-energize the apartment/house by turning off the main circuit breaker at the input switchboard or unscrewing the plugs on the electricity meter. RCDs, if any, are left on. This is necessary to make sure that the microwave does not siphon through the network and grounding wires.

Next, we put the turned on mobile phone in the microwave, close the door and try to call it from another one. It doesn’t matter where it’s from, even from Antarctica. It is important for us to make sure that the nearest cell does not pick up the marker signal of what is in the oven. As you know, cell phones, even when turned off, respond once a minute like “I’m online,” and the impulse from the phone’s transmitter is quite powerful.

So, if the call did not go through and a message arrived like “The called party’s phone is out of network coverage or turned off,” then everything is OK, the furnace shielding is in order and it can be tested more deeply. If the message was “Subscriber unavailable” or “Call failed,” then it means that the control phone marker has penetrated the cell, but the voice channel could not be established, the shielding of the oven is bad. What to do next with such a stove is at your discretion, in the American way: “You have been warned of the possible consequences.”

Siphon

Mobile phones operate in the 900 or 1800 MHz frequency range, and the phone's transmitter is much weaker than the magnetron. Therefore, you also need to check whether the microwave’s shielding from its own radiation is reliable enough. To do this, you will need 2 disposable plastic cups of water, an aluminum pan with a lid and a load of not very wet product that you don’t mind overbaking, for example, boiled jacket potatoes. The water in the cups should be the same temperature, equal to room temperature. Therefore, if the experiment is planned in advance, tap water needs to be poured into any clean container about 24 hours in advance, and water that is already in thermodynamic equilibrium with the environment must be poured into glasses: in order for a filled 200-ml container to arrive, it will take at least 2 -3 hours.

For the experiment, the product is loaded into the oven and the door is closed without starting the timer yet. Glasses of water are placed 10-40 cm in front of the oven door: one “naked”, the other in a covered pan. Water is measured into glasses using a beaker equally in the amount of 100-500 ml with an accuracy of no worse than 0.5 ml. We set the oven power regulator to maximum without grilling. If possible, it is better to turn off the camera backlight. The room should be as dark as possible and certainly there should be no direct light, incl. and from light bulbs. Now turn the timer knob to the maximum time (usually 30 minutes) and get out of harm’s way. The magnitude of the PES decreases with the square of the distance from the source, so it will be completely safe to go to another room.

As soon as the microwave bell rings, we return, turn on the light (you can now), remove the lid from the pan and, without touching the cups with your hands (!), measure the temperature of the water in them, carefully stirring with a temperature probe. If the temperature difference in the containers is less than 1 degree (this is double the intrinsic error of the temperature probe, although the tester shows the temperature in gradations of 0.1 degrees), then everything is OK - for an hour and a half a day, this microwave can be used according to Soviet standards. If it’s more, everything is again at your discretion, American style.

Checking the door

If a seemingly working microwave is siphoning, then most likely the gap between the closed door and the oven body is more than 0.15 mm. In RuNet they correctly write that you can check it with a sheet of writing paper with a density of 90-110 g/cubic. dm, it is just the right thickness, but the testing method they give is incorrect. It would be correct to cut a strip of paper 5-7 cm wide and place it under the door 6 times before closing: at the top and bottom at the hinges, then in the middle and at the latches. Each time the paper should not be pulled out from under the buried door. In this way, the door will be checked for distortion both horizontally and vertically, and it can be eliminated due to the play of the hinge fastening bolts in the mounting holes.

How does a microwave work?

Well, now you know enough about microwaves and microwave ovens to decide whether it’s worth taking on the repairs yourself. If such a desire remains, then in order to finally understand how a microwave oven works, where things can break in it, and where what degree of care needs to be taken when repairing it, you will have to turn to the circuit diagram of the microwave oven. Its typical structure, used in many models from Samsung and other manufacturers, is shown on the left in Fig. Highlighted in green is a surge protector designed to prevent microwave power from being released onto the microwave power wires (see below). Blue – control module with EMB system. Gorchichny - a device for generating power supply pulses to a magnetron (UFI). Formally, the UFI is included in the control module; their components are located on the same printed circuit board. But UFI malfunctions are specific, so functionally it should be considered separately. The power supply for the BPM magnetron is indicated in pink.

What is happening there

The mains filter contains a common fuse F1, which can blow in many cases, see below. If the fault that caused its burnout is eliminated, the new F1 must be set to the same rating (for the same current, time and response temperature) as the “native” one. F1 provides general protection for the oven against current overloads, so if the thought of a “bug” flashes through your mind, it is better to immediately switch it to a new microwave oven.

The thermal fuse (thermal fuse) is installed on the body of the hottest component - the magnetron - and is triggered many times: it is restored when it cools down. If the microwave oven turns off due to overheating before the programmer turns it off, it is a sign that the magnetron cooling exhaust fan, its outlet grille, or the inlet pipe are clogged. If the fan motor operates with knocking, creaking, or a lot of noise, its mechanical wear is likely, which requires replacing the motor.

EMB

Microswitches SWA, SWB and SWC make up the electromechanical interlock system. SWA and SWB are activated by the upper door latch, SWC by the lower. Since the microwave is a device of hazard class I and is often operated abnormally (without grounding), a complex EMB system is used: double for opening and control for short circuit. One of the principles of TB is implemented here: if it is impossible to avoid an invisible danger 100%, you need to at least make it visible. The invisible danger in this case is microwave radiation through a door that is not tightly closed, and the visible danger is the combustion of F1.

In view of the importance of the EMB for the safety of the oven and its susceptibility to breakdowns due to the sedimentation of fumes (see below), it is necessary to consider the EMB circuit in more detail separately from the general one already in the state with the door closed (see figure on the right). As you can see, if the SWA gets stuck when the door is open, the SWC will short-circuit the common power circuit, causing F1 to burn out. To avoid false alarms of the EMB, it is necessary for the SWC to switch a little slower than the SWA. Therefore, firstly, faulty SWA and SWC need to be replaced only with ones of the same type.

Secondly, a situation is possible when all the EMB mics ring normally both when the door is open and when the door is closed, but F1 burns out immediately when it is opened. This means that the fumes from the products penetrated into the mikriki, their response times “floated” and the EMB became unbalanced in time. There is only one way out - change SWA, SWB and SWC at once, because They are non-removable and cannot be repaired.

Note: The same microswitches for the electromechanical door lock must first be checked if the oven does not turn on when the door is closed. Very often their contacts simply do not close/switch due to the child adhering to them.

Fat and fumes

We immediately encountered the role of fat and its fumes in causing microwave malfunctions, and there will be even more troubles from it in the future. The fat in foods does not boil in the microwave, like in a frying pan, but evaporates, and its vapors settle anywhere, forming a film of fumes. It disrupts the mechanics, causing complex problems (see below). A slightly damp smoke film has noticeable conductivity, “confusing” the control automation, and a dry film breaks through with a voltage of less than 500V, which is dangerous for the high-voltage part. It is especially undesirable for children to get into the microwave path - repairing a microwave oven in this case turns out to be the most difficult and expensive.

To verify the ubiquity of fat vapors, you can do an experiment that requires a completely new frying pan with a lid. For now, keep the lid away, and melt any cooking fat in a frying pan until it spreads. Then they let it completely harden in the frying pan, cover it with a lid and keep it at room temperature for a day or more. After this, the lid turns out to be sticky to the touch - fatty fumes have settled on it. What will happen from fat in the oven chamber at a temperature of 100 degrees or more is a rhetorical question. Fat in the microwave is not dark, burnt, like kitchen fat, but almost transparent and therefore difficult to notice, but no less harmful.

Automatic control

Let's say our stove is still working. Product loaded and door closed. The power control (see below) is set correctly. Turn the timer knob to the desired time - SW1 will immediately close, turn on the backlight, table rotation, magnetron airflow and convector. When they “accelerate”, SW2 will work and turn on the magnetron power pulse generation device (UVI), the furnace will begin to heat. When the timer returns to zero, SW1 and SW2 will open, turning everything off, and the bell will ring. In simple microwave ovens, its spring is charged mechanically when the door is closed, and released by a lever that pushes the timer cam.

Timer

The microwave timer is an electromechanical cam programmer driven by the timer itself: a coil spring with a clock mechanism or a micromotor with a gearbox. Several disks with cams are mounted on the timer shaft, closing and opening contact groups.

Malfunctions of the timer (we will call it that for brevity) are most often caused by fatty children. Less often - breakdown of mechanical parts. Even less common, if the timer is completely mechanical, is by weakening the spring. Typical signs of timer failure are as follows:

After turning the control knob, the oven does not work at all, the knob does not rotate back - the mechanics are completely clogged or the micromotor or its gearbox has failed. Repair in the first case is overhaul and cleaning, in the second - replacement.
End functions do not work. For example, the backlight, table, magnetron blower and convector turn on, but the oven does not heat. Either the contacts (in this case SW2) are clogged, or its cam has broken off. Repair - as before. case.
The knob rotates back, goes to zero in the allotted time, the bell rings, but nothing turns on electrically. The same, only with SW1.
Everything works as it should, but slowly - the actual time the knob returns to zero is longer than the specified one. It rarely happens, and only with timers with a clock mechanism - its spring has weakened. Repair - wind it by 0.5-2 turns; Timers with clocks have this feature. In some, without disassembly: under the back cover there is a slot for a screwdriver for winding.

Oh, those “skis”...

In some old LG microwaves, due to fumes in the timer, a completely exotic breakdown occasionally occurs: the stove turns on spontaneously and “threshes” until it goes into a heat stop. When the FU cools down, it turns on again. Dangerous failure, because If the chamber is empty, the magnetron soon breaks down, and replacement turns out to be more expensive than a new furnace. It is most often observed in the off-season before turning on the heating, but only with the door closed. The reason, as it turns out, is that SW1 is stuck due to fumes and, at the same time, a lump of fumes between the contacts of SW2. Its resistance in damp air turned out to be commensurate with that of the timing resistors of the UVI (see below), the storage capacitor slowly charged and started the relay that supplied power to the magnetron.

Camera mechanics

The sedimentation of the child in the table rotation mechanism and the convector acts as a pumping action: due to uneven heating of the load, the release of fat vapors from overheated places intensifies. Eventually, the cover of the waveguide output window burns out, which means complex and expensive repairs to the microwave path. Therefore, if you notice uneven rotation of the table or the child is tightening the convector grates, you need, without waiting for the worst, to disassemble the stove and clean the mechanics. With the condition: do not touch the magnetron and microwave path, if the design of the furnace allows this. Otherwise, it is better to contact a service center; prices for such repairs are reasonable.

UVI and power

The device for generating magnetron power pulses operates in this way: through the low-power rectifier diode D1 and resistors R2/R3, the high-capacity electrolytic capacitor C4 is charged. Zener diode D2 is designed to protect low voltage C4 and RY relays from overvoltage. When the voltage on C4 reaches the trigger voltage RY, it will supply 220V 50/60Hz to the primary winding of the magnetron power transformer, which will output a microwave pulse into the chamber. After a short time C4 will discharge through the RY winding, it will release, then the cycle will repeat until the timer opens SW2 or FU fires. Thus, microwave pulses are supplied to the chamber (inset in the bottom center in the figure with the diagram).

In the simplest case, power adjustment is carried out by switching R2/R3. In this case, the charging time of C4 changes, but its discharge time remains unchanged. Accordingly, the ratio of the pulse repetition period to the pulse duration changes, the so-called. duty cycle of the pulse sequence. This is pulse width modulation (PWM), which, as we see, is by no means the prerogative of “digital” microwaves. The average power delivered by the magnetron, which the product load, due to its thermal inertia, perceives as constant, depends on the duty cycle of the pulses.

So that during a sudden power outage, the magnetron, due to the energy accumulated in the windings of the transformer, does not give a large surge of microwave frequencies that can siphon through any screen, the primary winding of the transformer is not completely disconnected from zero 220V, but remains connected to it through high resistance resistors R4. If they are removed, an otherwise serviceable stove will stubbornly siphon to any grounding. If the R4 soldering on the board becomes contaminated, the magnetron will process each pulse longer than it should, overheat, and the heater will shut down due to heat. So remember these “cutters” well.

A number of microwave oven models use double PWM, which ensures greater stability of the average magnetron power. To do this, additional disks with different numbers of cams and their own contact groups are installed on the timer shaft. Power adjustment is carried out by switching the UFI power supply from group to group. In this case, a series of power pulses comes in packets, following each other less frequently or more often (positions a and b in the figure), and the duty cycle of the pulses within the packet remains unchanged.

In UFI, the relay most often fails (see figure on the right) - its contacts need to switch a large current. The magnetron does not turn on and the oven does not heat, although everything else is fine. To check, the terminals of the RY winding are connected to an regulated power source, and a multimeter turned on in ohmmeter mode is connected to the terminals of the closing contacts. If, when the voltage on the winding increases from 3 to 24V, the tester does not show a short circuit, RY needs to be changed, regardless of whether the click of the triggered contacts was heard or not.

Another typical malfunction is that the stove heats less than what is set by the regulator knob. It develops gradually: to obtain the same heat, you need to turn the handle further and further. A possible reason is loss of capacity C4; it is replaced with a known good one of the same type.

Note: Another possible reason for the decrease in microwave power is the exhaustion of the magnetron’s life. Characteristic signs are that the furnace is more than 5 years old, it has been used intensively, and the drop in power develops much more slowly, not in days and weeks, as with the loss of capacity of a timing capacitor, but over the course of months. Accurate diagnostics - in a service center or production laboratory that has the appropriate equipment.

Finally, every now and then there is a sudden bang and the oven stops heating. Upon opening, it turns out that the C4 body is swollen and cracked. The reason is that D1 is broken or D2 is out of order. In addition to replacing both of them at once and C4, you must definitely check RY, as described above - its winding could very well burn out.

High voltage stand

During the repair of the high-voltage part (magnetron IP), it will be necessary to ring its components. An ordinary tester “does not pick up” them; its battery voltage is not enough. In RuNet it is advised to check high-voltage (HV) components using a 15-25 W 220V incandescent test lamp. “Ringing” a circuit using a “control” is, firstly, directly prohibited by the PTB. Secondly, this method is very crude and does not give a 100% reliable result.

A homemade stand for testing explosive components (see figure on the right) is, first of all, completely safe: the input impedance of the multitester at the measurement limit of 750V AC is several megohms. If you accidentally touch the blue end of the wire according to the diagram, the sensations will be no greater than when using a phase indicator. You just need to mark on the body of the socket where the phase is (determined by the same phase indicator), on the plug - which pin the red wire in the diagram goes to, and insert the plug into the socket so that the marks match.

In addition, this stand is much more sensitive and allows you to find even potentially faulty elements that cause intermittent malfunctions in the operation of the furnace:

The tester shows almost full network voltage - the component is short-circuited.
The voltage is incomplete, but quite high (tens of volts) - breakdown under operating voltage; the control “catches” him uncertainly.
The voltage is low, a few volts - leakage under operating voltage. The component is still half-dead, but it will break through soon. The control system will react to this as if it is working properly.

Note: However, remember - any manipulations with the component being tested (connection, disconnection, switching) can only be performed by removing the plug from the socket!

Magnetron power supply

Due to the pulsed mode of its operation, the high-voltage power supply of the magnetron is made using a half-wave circuit with doubling the voltage. Do not try to build one like this for your needs - its transformer must be designed to operate in short-circuit mode on the secondary winding for 5 minutes.

The positive half-wave from the secondary winding of the transformer, closing through the high-voltage diode D, charges the high-voltage capacitor C to its amplitude voltage of 2000 V. The negative half-wave through the same diode charges it to 4 kV, as in the voltage booster of old TVs. The magnetron under such an emitter voltage (negative relative to the common wire) begins to generate microwave frequencies, C is discharged and everything repeats all over again.

High-voltage fuse F and discharge resistor R are protective. The first one turns off the magnetron when it is instantly overloaded to the point of overheating (for example, when the chamber is empty or overloaded, there are metal objects or unsuitable products in it, or when a high-voltage diode breaks down). Through R, the capacitor quickly discharges, which saves the microwave from “splashing out” when the door is suddenly opened while the oven is running.

In this circuit, when F burns out, a microwave splash outward is possible in case of poor-quality shielding and/or grounding, because An electric arc burns in a blown fuse for several milliseconds. Therefore, a number of microwave oven models use a magnetron power supply circuit with a protective diode (see figure on the right). Microwave bursts are excluded in it, but the bad thing is that the protective diode is as disposable as a fuse, breaks more often, and costs the same as a high-voltage capacitor. The protective diode is checked on the stand described above, just like the high-voltage one: when you turn it on in both the forward and reverse directions, the tester should show approx. half the mains voltage. If the difference is more than 20%, it is faulty, although “scrolling” with an induction megger and a control test will pass normally.

Any malfunction of the HV IP leads to the fact that the oven does not heat, although all its other functions are operational. In this case, F necessarily burns out. This is basically the same fuse, only with a spring-loaded thread for faster opening. Called by a regular tester. The high-voltage capacitor is tested on the stand described above; the tester should show 10-70 V in both directions, depending on the capacity of this sample (indicated on the case).

Transformer

After checking as many as 4 explosive components, you need to check the magnetron power transformer. The microwave may not heat due to an interturn short circuit in its windings (turn short circuit). It is not determined by the continuity tester, because has almost no effect on the active resistance of the windings. It is best to submit a suspicious transformer for inspection to a company specializing in electrical measurements (not electrical installation work!) or to the electrical measuring laboratory of the Distribution Zone or Consumer Supervision. The prices for such a service are divine everywhere.

If it is not possible to get to the laboratory, then with a high degree of confidence you can check the transformer at home. The technique is based on the fact that in the presence of a turn short circuit, the no-load current of the transformer increases several times. Here you will have to commit a violation by using the same control lamp at 220V 15-25 W. You can’t determine it on the bench: the current through the tester in voltmeter mode is too small, and measuring in ammeter mode is very dangerous.

The control is connected in series with the high-voltage winding. It is with high voltage, but on the other hand it is extremely dangerous! Finding the high-voltage winding is not difficult; it is heavily insulated and, together with the filament winding, is wrapped in additional insulation, see fig. on right. The assembled circuit is briefly connected to the network, for no more than 5-10 s. If the transformer is working properly, the light bulb will either not light up at all, or its filament will heat up to a dull red. If there is a noticeable glow, there is also a turn short circuit.

Without experience, it can be difficult to determine: what does “dull red” and “noticeable glow” mean? To be sure, we will arrange an artificial orbital one. Let's disconnect the circuit from the network (!!!), short-circuit the filament winding and briefly plug it into the network again. The light bulb should flash much brighter than in the first case. If the glow has not changed or changed only slightly, the transformer “twists” and is unusable.

Magnetron

If all high-voltage components are checked, but there is still no microwave generation, then the problem is probably in the magnetron. Without removing it or disassembling the microwave path, you can use a regular tester to check the magnetron for internal short circuit. It occurs due to peeling of the cathode coating, which closes the gap between it and the anode.

Almost as often as an internal short circuit, a breakdown of the cathode filter occurs in the magnetron (shown by the red arrow on the left in the figure). This is not just a connector, but a pair of high-voltage feed-through capacitors. It is impossible to pick out the filling of the capacitors (in the center in the figure), this, firstly, is unlikely to show anything; secondly, its crumbs and, especially, dust are toxic. First of all, you need to measure the resistance between the terminals with a regular tester. It should be close to zero: the terminals are connected to the filament, and its current is approx. 10A at 6.3V.

You need to carefully unscrew the clip with feed-through capacitors; in many cases this can be done without removing the magnetron and without touching the microwave path. Most likely, the breakdown will be visible immediately (on the right in the figure); if not, carefully bite the clip off the filter inductances and ring each terminal on the flange on the bench. If the “passes” are working properly, the tester will show zero in each case. If there is at least a couple of volts, there is a hidden breakdown or voltage leak. If everything seems to be in order, but the oven still does not heat, the cathode has suddenly completely lost emission and the magnetron is unusable. This happens with magnetrons, high-power generator klystrons and traveling wave tubes (TWTs); the reason is depressurization of the housing, which should have a deep vacuum. What else is possible with a magnetron - the magnets become demagnetized due to overheating. In this case, when turned on, the high-voltage fuse will immediately burn out.

Camera

According to the logic of the presentation, the microwave chamber is the last one, but because of it, it is where the most breakdowns occur. A disaster like the one in pos. 1 Fig., may not be as scary as the eyes see: the camera coating is generally designed for such cases. Unless you tried to cook eggs in the microwave, the boiled denatured protein eats firmly into the coating, which means a new oven. You need to carefully remove debris from the camera, wash it with a detergent recommended by the manufacturer and inspect for scratches deeper than the eye, 0.1 mm. After this, we check by hand the smooth rotation of the table and do a shielding and “siphon” test. The likelihood that the oven will be suitable for further use is not small. If the coating burns through (item 2), the problem is at seams - a new stove is needed. No matter how you repair it, the siphoning will be “direct fire right through.”

Perhaps the most common malfunction of household microwave ovens is that everything works as it should, everything is loaded as it should be and what was previously heated without problems, but there is sparking in the chamber. Then, with clean hands in a clean, dry room, carefully remove the protective cover of the waveguide output window - if it is removed from the outside, without disassembling the microwave path. The lid is made of muscovite mica or mica cloth and is quite fragile. The outer side of the cover may appear clean or have subtle damage, but on the waveguide side a completely different picture is revealed, pos. 3 and 4. It was the evaporation of fat and fat fumes that worked.

The cover needs to be replaced with exactly the same one. Homemade kulibins vying with each other to offer: I cut them out of 1.5 mm material! The resource is four times longer - proprietary 0.4 mm! In fact, mica is not ideally transparent for the microwave; a thick lid will heat up, strongly absorb fat vapors and will last less than the original one. But the main thing is that the furnace will lose its mode and start siphoning “almost at a run.”

If the microwave has a short path, then under the cover the inside of the waveguide (more precisely, the output resonator) and the antenna (emitter) of the magnetron will be visible. The resonator, if its coating is not swollen, cracked or discolored, can be cleaned with alcohol as described above. The darkened emitter needs to be replaced with a new branded one; it is simply removed from the magnetron. To do this, the old emitter stuck in the socket is very carefully swung with small pliers, and the new one must be placed with a latex glove so as not to get dirty or scratched.

There are three subtleties here. First, never remove the magnetron yourself. Second, do not try to extend the life of a punctured (burnt out) emitter by turning it over. In both cases, the oven goes astray and the “siphon” cannot be eliminated. Third, after any repair during which you even touched the microwave path with your finger, be sure to check the microwave for shielding and microwave leakage, as described above.

Finally

A completely legitimate question after reading: is it worth keeping a device that is so dangerous at home? There is no absolute evil, just like there is no absolute good. At the pace of modern life, it is sometimes very difficult to do without a microwave oven, and the absence of fat hydrolysis is a strong argument in its favor.

The author has worked professionally with microwaves for many years. There were no health consequences: I was always extremely careful, and individual sensitivity turned out to be low. There is a microwave on the farm, it’s inexpensive. It stands mostly with the plug removed; It turns on very rarely and irregularly, when it is impossible to do without it.

This is how you should treat household microwave ovens: as an inevitable, but sometimes useful evil. Like a can of dichlorvos or a propane torch - sometimes you need it and there is no replacement, but these are not things for pampering and amateurish experiments. And most importantly, check the microwave at least once every six months for the quality of shielding and microwave leakage.

A magnetron is a special electronic device in which the generation of ultra-high-frequency oscillations (microwave oscillations) is carried out by modulation of the electron flow in speed. Magnetrons have significantly expanded the scope of heating with high and ultrahigh frequency currents.
Less common are amplitrons (platinotrons), klystrons, and traveling wave tubes based on the same principle.

The magnetron is the most advanced high-power ultrahigh-frequency generator. It is a well-evacuated tube with electron flow controlled by electric and magnetic fields. They make it possible to obtain very short waves (up to fractions of a centimeter) at significant powers.

Magnetrons use the movement of electrons in mutually perpendicular electric and magnetic fields created in the annular gap between the cathode and anode. An anode voltage is applied between the electrodes, creating a radial electric field, under the influence of which electrons ejected from the heated cathode rush to the anode.

The anode block is placed between the poles of an electromagnet, which creates a magnetic field in the annular gap directed along the axis of the magnetron. Under the influence of a magnetic field, the electron deviates from the radial direction and moves along a complex spiral trajectory. In the space between the cathode and anode, a rotating electron cloud with tongues is formed, reminiscent of the hub of a wheel with spokes. Flying past the slits of the anode volumetric resonators, electrons excite high-frequency oscillations in them.

Rice. 1. Magnetron anode block

Each of the volumetric resonators is an oscillatory system with distributed parameters. The electric field is concentrated at the slits, and the magnetic field is concentrated inside the cavity.

Energy is removed from the magnetron using an inductive loop placed in one or more often two adjacent resonators. The coaxial cable supplies energy to the load.

Rice. 2. Magnetron design

Heating by microwave currents is carried out in waveguides of round or rectangular cross-section or in volumetric resonators, in which the simplest forms TE10(H10) (in waveguides) or TE101 (in volumetric resonators) are excited. Heating can also be carried out by emitting an electromagnetic wave onto the heating object.

The magnetrons are powered by rectified current with a simplified rectifier circuit. Very low power installations can be powered by alternating current.

Magnetrons can operate at various frequencies from 0.5 to 100 GHz, with powers from several W to tens of kW in continuous mode, and from 10 W to 5 MW in pulsed mode with pulse durations mainly from fractions to tens of microseconds.

Encyclopedic YouTube

1 / 5

✪ ✅Homemade MAGNETRON GUN from a microwave and a stun gun

✪ ✅What a microwave can do! High voltage arc

✪ Magnetron

✪ What is a magnetron?

✪ Emp Jammer / How to make a pocket EMP emitter with your own hands!

Subtitles

I want to present you with our new invention, an electromagnetic gun and show what it is capable of against a moped of loud music and spy equipment. The source of microwave radiation is the magnetrons that I took out of the microwaves, they are powered by a high-voltage pulse from a stun gun, the secret of long range is in the correct coordination of the magnetrons and the horn antenna, which was it’s difficult to achieve using a powerful shocker with amplified power and combat capacitors, it’s time to show it in action; first, we removed all valuable electronics and put on protective shielding suits made of foil; you can check the presence of a powerful electromagnetic field using light bulbs. Since under the influence of radiation they begin to glow, we turn on the glow on our magnetrons and what is happening there now, I’ll zoom in, let’s keep the lights blinking, now let’s check how effective this gun is against spy equipment, as we see the bug works, its sensitive microphone perfectly picks up the speech of neighbors and transmits Let's try to irradiate my phone from a 15 meter distance, strong interference is heard, but it still continues to work, come closer, about twice, even three times, maybe the signal is gone, the bug is neutralized, well, it's time to test our gun on something more serious and we went out of town to irradiate the scooter - wow - what happened? - I don’t know, I, I, I, him... .... has this... stalled? Something shorted out, look how much smoke there is, damn it, what happened? Look at the battery there, maybe the strap needs to be removed. The house smells like burnt wiring, so how do you drive it? well, let me try to start it, the leg doesn’t come back, we’ve finished playing with the magnetron and now we’ll have to go push it like this! Pushing a scooter home through the city, what happens, why does a magnetron gun so easily disable electronics, the whole secret is in powerful pulses, high-voltage shock discharges feed magnetrons, which generate short but powerful electromagnetic pulses. electrical circuits in technology capture these impulses, turning them into electricity, which penetrates and destroys the semiconductors in them, but it does less harm to living organisms since the heating from short impulses is less than in a microwave, so a foil suit is enough to protect against harmful radiation, and now I’ll try this Magnetron blaster against loud music, shall we turn it on? - My hat is shaking! - okay, now we’ll test it! To be honest, we'll try through this wall, turn on the heat, remove the shocker from the fuse, everything is ready, let's go, it's buzzing scary, everything works - you just turned up the volume, right? - Yes, in general, this gun did not destroy, but we will try from the nearest one through one wall. Let's see how the effect will be, let's go - oh! damn, what happened? Don't know!@#% ! but the equipment had a hard time after long checks, it turned out that the electronic ignition, wiring and, strangely enough, the battery burned out in the scooter, I replaced the ignition relay, the variator belt and cleaned the muffler and the scooter began to ride even better than before the magnetron. If you want more crazy inventions then support the channel with a subscription Ah ah ah! saved!

Story

In 1912, the Swiss physicist Heinrich Greinacher was studying ways to calculate the mass of an electron. He assembled a setup in which an electric vacuum diode with a cylindrical anode around a rod-shaped cathode was placed inside a magnet. He was unable to measure the mass of the electron due to problems with obtaining a sufficient level of vacuum in the lamp, but in the course of his work, mathematical models of the movement of electrons in electric and magnetic fields were developed.

French scientist Maurice Pont and his colleagues from the Parisian company KSF in 1935 created an electron tube with a tungsten cathode surrounded by resonator anode segments. It was the predecessor of magnetrons with resonator chambers.

The design of the multicavity magnetron Alekseev - Malyarov, providing 300-watt radiation at a wavelength of 10 centimeters, created in 1936-39, became known to the world community thanks to the publication of 1940 (Alexeev N. F., Malyarov D. E. Getting powerful vibrations of magnetrons in centimeter wavelength range // Magazine of Technical Physics. 1940. Vol. 10. No. 15, P. 1297-1300.)

The Alekseev-Malyarov multicavity magnetron owes its appearance to radar. Work on radar began in the USSR almost simultaneously with the beginning of radar work in England and the USA. According to foreign authors, by the beginning of 1934 the USSR had advanced more in this work than the USA and England. (Brown, Louis. A Radar History of World War II. Technical and Military Imperatives. Bristol: Institute of Physics Publishing, 1999. ISBN 0-7503-0659-9.)

In 1940, British physicists John Randall and Harry Boot invented resonant magnetron. The new magnetron produced high-power pulses, which made it possible to develop a centimeter-wave radar. Short wavelength radar allowed the detection of smaller objects. In addition, the compact size of the magnetron led to a sharp reduction in the size of radar equipment, which made it possible to install it on aircraft.

In 1949, in the USA, engineers D. Wilbur and F. Peters developed methods for changing the magnetron frequency using voltage control (mitron device).

Characteristics

Magnetrons have high efficiency (up to 80%).

Magnetrons can be either non-tunable or tunable over a small frequency range (usually less than 10%). For slow frequency tuning, hand-driven mechanisms are used; for fast frequency tuning (up to several thousand tunings per second), rotary and vibration mechanisms are used.

Magnetrons as ultrahigh frequency generators are widely used in modern radar technology (although they are beginning to be replaced by active phased array antennas) and in microwave ovens. In fact, as of 2017, the magnetron is the last type of mass-produced electric vacuum device after the production of picture tubes was curtailed at the beginning of 2010.

Design

Resonant magnetron consists of an anode block, which is, as a rule, a thick-walled metal cylinder with cavities cut into the walls, acting as volumetric resonators. The resonators form a ring oscillatory system. A cylindrical cathode is attached to the anode block. A heater is fixed inside the cathode. A magnetic field parallel to the axis of the device is created by external magnets or an electromagnet.

To output microwave energy, as a rule, a wire loop is used, fixed in one of the resonators, or a hole from the resonator to the outside of the cylinder.

The magnetron resonators form a ring oscillating system, around them the interaction of an electron beam and an electromagnetic wave occurs. Since this system, as a result of the ring structure, is closed on itself, it can be excited only by certain types of vibrations, of which important is π -view. Among several resonant frequencies of the system (with N resonators in the system, the existence of any integer number of standing waves in the range from 1 to N/2 is possible), the π-type of oscillations is most often used, in which the phases in adjacent resonators differ by π . If there are other resonant frequencies near the operating frequency (closer than 10%), frequency jumps and unstable operation of the device are possible. To prevent such effects in magnetrons with identical resonators, different connections can be introduced into them, or magnetrons with different resonator sizes can be used (even resonators with one size, odd resonators with another).

Individual magnetron models may have different designs. Thus, the resonator system is made in the form of several types of resonators: slot-hole, blade, slot, etc.

Principle of operation

Electrons are emitted from the cathode into the interaction space, where they are affected by a constant anode-cathode electric field, a constant magnetic field and an electromagnetic wave field. If there were no electromagnetic wave field, electrons would move in crossed electric and magnetic fields along relatively simple curves: epicycloids (the curve described by a point on a circle rolling along the outer surface of a circle of larger diameter, in this particular case, along the outer surface of the cathode). With a sufficiently high magnetic field (parallel to the axis of the magnetron), an electron moving along this curve cannot reach the anode (due to the Lorentz force acting on it from this magnetic field), and they say that magnetic blocking of the diode has occurred. In the magnetic blocking mode, some of the electrons move along the epicycloids in the anode-cathode space. Under the influence of the electrons' own field, as well as statistical effects (shot noise), instabilities arise in this electron cloud, which lead to the generation of electromagnetic oscillations, these oscillations are amplified by resonators. The electric field of the resulting electromagnetic wave can slow down or speed up the electrons. If an electron is accelerated by the wave field, then the radius of its cyclotron motion increases and it is deflected in the direction of the cathode. In this case, energy is transferred from the wave to the electron. If the electron is decelerated by the field of the wave, then its energy is transferred to the wave, while the cyclotron radius of the electron decreases, the center of the circle of rotation shifts closer to the anode, and it is able to reach the anode. Since the anode-cathode electric field does positive work only if an electron reaches the anode, energy is always transferred primarily from the electrons to the electromagnetic wave. However, if the speed of rotation of electrons around the cathode does not coincide with the phase speed of the electromagnetic wave, the same electron will be alternately accelerated and decelerated by the wave, as a result, the efficiency of energy transfer to the wave will be small. If the average speed of rotation of the electron around the cathode coincides with the phase speed of the wave, the electron can remain continuously in the decelerating region, and the transfer of energy from the electron to the wave is most efficient. Such electrons are grouped into bunches (so-called “spokes”), rotating along with the field. Repeated, over a number of periods, interaction of electrons with the RF field and phase focusing in the magnetron provide a high efficiency and the possibility of obtaining high powers.

Application

In radar devices, the waveguide is connected to an antenna, which can be either a slot waveguide or a conical horn feed paired with a parabolic reflector (the so-called “dish”). The magnetron is driven by short, high-intensity pulses of applied voltage, resulting in a short pulse of microwave energy being emitted into space. A small portion of this energy is reflected from the radar object back to the antenna and enters a waveguide, which directs it to a sensitive receiver. After further processing of the signal, it eventually appears on a cathode ray tube (CRT) as radar map A1.

In microwave ovens, the waveguide ends in a hole that is transparent to radio frequencies (directly in the cooking chamber). It is important that there is food in the oven while the oven is operating. The microwaves are then absorbed instead of being reflected back into the waveguide, where the intensity of the standing waves can cause sparking. Sparking that continues long enough can damage the magnetron. If you are cooking a small amount of food in a microwave oven, it is better to also put a glass of water in the oven to absorb the microwaves.

Notes

, With. 353.
H. Greinacher (1912) "Über eine Anordnung zur Bestimmung von e/m" (On the apparatus for determining e/m), Verhandlungen der Deutschen Physikalischen Gesellschaft, 14 : 856-864. (German)

Microwave ovens (microwave ovens) have long become the most common household appliance, with the help of which you can very quickly defrost food, reheat already cooked food or prepare a dish according to an original recipe, and even disinfect kitchen cleaning sponges and rags that do not contain metal.

The presence of a convenient, intuitive interface, as well as multi-level protection, allows even a child to cope with the control of such a complex and high-tech device as a microwave oven. Some dishes can be easily and quickly prepared using built-in programs. And possible malfunctions can be completely eliminated by doing.

Heating of products placed in the microwave chamber occurs due to exposure to powerful electromagnetic radiation in the decimeter range. In household appliances, a frequency of 2450 MHz is used. Radio waves of such high frequency penetrate deep into the products and affect polar molecules (mainly water in products), causing them to constantly shift and line up along the electromagnetic field lines.

This movement increases the temperature of the food, and heating occurs not only from the outside, but also to the depth to which radio waves penetrate. In household microwave ovens, the waves penetrate 2.5-3 cm deep, they heat the water, which, in turn, heats the entire volume of food.

The magnetron device is the main component

Radio waves with a frequency of 2450 MHz are generated by a special device - magnetron, which is an electric vacuum diode. It has a massive copper cylindrical anode, round in cross-section and divided into 10 sectors with the same copper walls.

In the center of this structure there is a rod cathode, inside of which there is a filament. The cathode serves to emit electrons. At the ends of the magnetron there are powerful ring magnets, which create a magnetic field inside the magnetron necessary for generating microwave radiation.

A voltage of 4000 Volts is applied to the anode, and 3 Volts to the filament. There is an intense emission of electrons, which are picked up by a high-intensity electric field. The geometry of the resonator chambers and the anode voltage determine the generated frequency of the magnetron.

Energy is collected using a wire loop connected to the cathode and led into the emitter-antenna. From the antenna, microwave radiation enters the waveguide, and from it into the microwave chamber. The standard output power of magnetrons used in household microwaves is 800 W.

If less power is required for cooking, this is achieved by turning on the magnetron for certain periods of time, followed by a pause.

To obtain a power of 400 W (or 50% of the output power), you can turn on the magnetron for 5 seconds and turn it off for 5 seconds during a 10-second interval. In science it's called pulse width modulation.

During operation, the magnetron generates a large amount of heat, so its body is placed in a plate radiator, which during operation should always be blown by an air flow from the fan built into the microwave. When overheated, the magnetron very often fails, so it is equipped with protection - a thermal fuse.

Thermal fuse and why it is needed

To protect the magnetron from overheating, as well as the grill, which is equipped with some models of microwave ovens, special devices called thermal fuse or thermostat. They are available in different temperature ratings, indicated on their body.

The operating principle of a thermal relay is very simple. Its aluminum body is attached using a flange connection to the place where it is necessary to control the temperature. This ensures reliable thermal contact. Inside the thermal fuse there is a bimetallic strip that has settings for a certain temperature.

When the temperature threshold is exceeded, the plate bends and actuates a pusher, which opens the contact group plates. The power supply to the microwave oven is interrupted. After cooling, the geometry of the bimetallic plate is restored and the contacts close.

Purpose of microwave oven fans

The fan is the most important component of any microwave, without which its operation would be impossible. It performs a number of important functions:

Firstly, the fan blows on the main part of the microwave oven - the magnetron, ensuring its normal operation.
Secondly, other components of the electronic circuit also generate heat and require ventilation.
Thirdly, some microwave ovens are equipped with a grill that is necessarily ventilated and protected by a thermostat.
And finally, the food being cooked in the chamber also generates a large amount of heat and water vapor. The fan creates a slight excess pressure in the chamber, as a result of which the air from the chamber along with heated water vapor comes out through special ventilation holes.

In the microwave, from one fan, which is located at the rear wall of the case and sucks in air from outside, a ventilation system is organized using air ducts, directing the air flow to the magnetron plates and then into the chamber. The fan motor is a simple single phase AC motor.

Microwave oven protection and locking system

Any microwave oven has a powerful radio-emitting device inside - a magnetron. Microwave radiation of such power can cause irreparable harm to the health of humans and all living beings, so it is necessary to take a number of protective measures.

The microwave has a completely shielded metal cooking chamber, which is additionally protected from the outside by a metal casing that does not allow high-frequency radiation to penetrate outside.

The transparent glass in the door has a screen made of a metal mesh with a fine mesh, which does not allow radiation of 2450 Hz, wavelength 12.2 cm, generated by the magnetron, to pass out.

The issue of saving energy consumption has always been relevant. One of the types of lighting devices that will significantly help reduce electricity consumption in the home is. To make the best choice, you just need to understand the advantages and disadvantages of each type of such lamps.

Due to their features, double switches are widely used at home. How to properly connect such switches and what you need to know to prevent errors in this case can be read in.

The microwave door fits tightly to the cabinet and it is very important that this gap maintains its geometric dimensions. The distance between the metal body of the camera and the special groove in the door should be equal to a quarter of the wavelength of microwave radiation: 12.2 cm/4 = 3.05 cm.

A standing electromagnetic wave is formed in this gap, which has a zero amplitude value exactly where the door adjoins the body, so the wave does not propagate outward. This is an elegant way to solve the issue of protection from microwave radiation using the microwave waves themselves. This method of protection in science is called a microwave choke.

To prevent the microwave oven from turning on with the chamber open There is a system of microswitches that control the position of the door. Usually there are at least three such switches: one turns off the magnetron, the other turns on the backlight even when the magnetron is not working, and the third serves to “inform” the control unit about the position of the door.

The microswitches are located and configured so that they operate only when the microwave working chamber is closed.

Microswitches on the door are also often called limit switches.

The control unit is the brain of the device

Any microwave oven has a control unit and it performs two main functions:

Maintaining the set microwave power.
Turning off the oven after the set operating time has expired.

On older models of electric furnaces, the control unit consisted of two electromechanical switches, one of which set the power, and the other set the time period. With the development of digital technologies, electronic control units began to be used, and now microprocessor ones, which, in addition to performing two main functions, can also include many necessary and unnecessary service ones.

Built-in clock, which can certainly be useful.
Power level indication.
Changing the power level using the keyboard (push-button or touch).
Cooking or defrosting food using special programs “hardwired” into the memory of the control unit. In this case, the weight is taken into account, and the stove itself will select the required power.
Signaling the end of the program with the selected sound.

In addition, modern models have upper and lower grills and a convection function, which are also controlled by the control unit.

The control unit has its own power source, which ensures operation of the unit in both standby and operating modes. An important component is the relay unit, which switches the power circuits of the magnetron and grill, as well as the fan, built-in lamp and convector circuits according to commands. The control unit is connected by cables to the keyboard and display panel.

An entertaining video about the operating principle of microwave ovens

Look how simple it is to explain why this amazing device works.

Unfortunately, all equipment has its own service life, and microwave ovens are no exception. Sometimes we find that it takes longer to heat up a dish than usual. And sometimes the device seems to work properly, but the food remains cold. Often the reason for this microwave behavior is a faulty magnetron. Where is this part located and how to check it?

Microwaves can vary greatly from one another, but there is one detail without which no existing model, be it Samsung, Philips or another well-known brand, can work.

Everything depends on a high-quality magnetron.

What does this part consist of?

To emit waves, the device is equipped with a special antenna.
To isolate the antenna from the working surface, a special cylinder made of high-quality metal is used.
A special magnetic circuit is responsible for the distribution of magnetic fields.
But magnets are responsible for the distribution of flows.
To ensure that the part does not overheat, an important component for it is a radiator.
To prevent microwave radiation from causing harm, the magnetron is equipped with special filters.

Such a design as a magnetron is understandable only to professionals. Repairing it yourself is a labor-intensive and thankless process. If you are sure that this is the problem, it is better to contact a specialist.

What problems may arise

Having studied the magnetron design, it becomes clear that not the entire part fails. Perhaps some of its parts are not working, which needs to be installed. There are several common causes of failure. How to check the magnetron and find out where exactly the fault lies?

One of the important components of the magnetron is a special cap that maintains the vacuum of the pipe. If this is the problem, replacing it will not be difficult.
If the part overheats, it means the radiator has failed.
Overheating may cause the filament to break. To diagnose this malfunction you will need a special tester. In working condition, the thread shows a voltage of 5-7 Ohms. If it fails, the voltage will drop to 2-3 Ohms, but if a break occurs, the device will show infinity.
Filter failure is checked by a tester. If the part is working properly, the device will show infinity; if it breaks, you will see the numerical resistance.

There are breakdowns that you cannot diagnose on your own. To do this, you need to have not only knowledge, but also special equipment.

How to check the magnetron

The cost of replacing this part is so high that many people prefer to purchase a new microwave rather than repair the old one. Before you send a damaged device to the trash, you need to make sure that the problem is in this expensive part. To do this, you need to do certain manipulations:

The first thing you should do to test the magnetron is turn off the power to the microwave by unplugging the device.
Inspect the inside walls of the microwave oven. If the magnetron malfunctions, you will find melted areas, darkened or burnt walls.
If there are no external signs, it is necessary to diagnose with a tester.
Check if the fuse is good.

The main signs that the magnetron has failed are strange sounds, smoke or. After such external manifestations, the microwave stops working correctly.

Installing a new part

If you have an expensive microwave model, then it is wiser to replace the broken part rather than buy a new stove. Of course, it is best to contact a service center, but you can try to replace it yourself.

When buying a new magnetron, pay attention to the same power, contacts and mounting holes. Otherwise, you risk purchasing a useless part.

Connecting a new magnetron is not difficult, since it has only two main contacts. Detailed information about all symbols is on the diagram; the main thing is to check the compliance of the following parts of the device:

The antenna must match the diameter of the factory one.
Make sure that the new device is firmly attached to the waveguide.
The length of the faulty antenna must match the new one.

It’s best to unscrew the old part and take it to the service center so that the specialists can select the one you need.

Conclusion

A microwave is an indispensable assistant in any kitchen. With its help, you can quickly heat up food and prepare a delicious dish. The breakdown of this technical miracle causes some stupor and paralyzes the usual rhythm of life. Many of these problems can be solved on your own, but if the magnetron fails, contact a specialist. Carrying out repairs yourself is dangerous not only for the equipment, but also for you.

All about car tuning