A microwave works in almost every modern apartment. This convenient household appliance can heat, defrost, and bake. Some models are capable of grilling and executing complex programs to create finished dishes inside. The operating principle of a microwave oven has not changed since its invention. But thanks to technological progress, the safety of the equipment has increased, and the electrical circuit is capable of complex control and precise control of operating parameters.
General operating principle of a microwave oven
The physics of the process of heating the contents of a microwave oven is quite simple. Microwave radiation affects the molecules of products, and due to their mutual friction, heat is released. But this is too simple an explanation.
In fact, only water molecules undergo vibrations. But if you put an ideally clean glass of distilled liquid in the microwave, its temperature will change quite little during the standard operating time of the oven. So why do foods heat up? This occurs due to the friction of molecules at the boundary of media, that is, different substances. And since the structure of any material, be it an edible product or a piece of wood, is large and necessarily contains water in the structure, fluctuations of different amplitudes arise.
Important! The frequency of the microwave oven is designed to have maximum effect on the molecules of the liquid. It is they, with their intense vibration and friction against neighbors, that contribute to the release of large amounts of heat. Materials that are dry and pure in chemical composition heat up very slowly, but there are few of these in nature.
Metals should not be placed in the microwave. When exposed to microwave radiation, surface currents are formed and spark and arc breakdowns occur on the walls of the internal compartment of the furnace. However, technological progress has found a way out. Today, many companies, such as Daewoo, produce microwave ovens in which metal objects can be placed. Also, many models allow the use of closed contours, in particular, plates with foil stamping on the edge or decorative dishes with a metal edge.
Repair features
One of the most common malfunctions is due to the fact that the microwave does not respond in any way to opening the door and operating the equation panel. It happens no less often that the oven does not heat, although it shows signs of operability: the lights are on, the glass table is rotating.
If there is no response to launch
First you need to check whether current is flowing to the surge protector. To do this, the casing is removed, and the high-voltage capacitor is forcibly discharged. Check the power cord with a multimeter. All wires running from the socket to the terminals must be connected. The grounding terminal must be connected to the housing.
If the wire is intact, then you need to check the condition of the mains fuse. It can be found on the filter board. In case of malfunction, you will have to install the same one. It is important to take into account that a more serious malfunction caused the fuse to burn out - it would not be superfluous to inspect the microwave.
When performing a visual inspection, it is better to use a flashlight and a magnifying glass. The following factors indicate a problem:
- breakdowns and abnormal holes in elements;
- darkening similar to burning;
- swollen capacitors or deformation of other elements.
The sense of smell will help diagnose the problem. The smells of burnt insulation, failed printed circuit boards or transformer oil are quite strong and therefore easy to detect. If you understand where the smell is coming from, you can localize the problem.
Light without heating
Often this situation is caused by faults with the high-voltage circuit or magnetron. But before checking these components, you need to inspect the camera. You need to make sure that there are no burnt holes, dirt or worn out enamel anywhere. The rectangular plate of radiotransparent dielectric located on the left must be removed and examined especially carefully. To do this, you will have to wash it with alcohol.
If there are through holes or dark spots on the plate, it will have to be replaced. Most likely, this happened due to the fact that metal utensils were placed inside the oven or they forgot about timely cleaning.
You need to check the safety diode in the magnetron circuit. If it burns out, then just install a new one. The part must have original parameters.
A burnt-out antenna cap indicates the need to replace the magnetron. The same applies to breakdowns in the housing. If the microwave oven has been in service for more than five years, then repair may not be advisable - it is more economical to buy new equipment.
What elements are included in the design of a microwave oven?
The design of a microwave oven seems complicated only at first glance. The owner of this device is misled by the number of buttons, indicators, and programming tools. In fact, any oven, with mechanical control, touch panel, remote control, hybrid electronic control, consists of the same functional blocks:
- microwave radiation generation unit, magnetron and waveguides;
- voltage conversion system, main module - step-up high-voltage transformer;
- control means as part of a group of sensors;
- secondary protection system;
- microwave control circuit.
Important! Depending on the complexity of the stove model, it may include a variety of options. For example, a grill, secondary wave scatterers, additional microwave generation units.
It is worth considering the operation of each unit separately, in the order in which they are used in a standard microwave usage scheme.
Control circuit
The main electrical circuit of the microwave that the user deals with is the control unit. In it, using buttons, mechanical switches, and regulators, boundary parameters are set. That is, operating power or mode, program execution time, and so on.
The control scheme can be as complex as you like. The simplest option is circular regulators, one of which is a timer relay. With their help, the mode power and operating time are set. Another option familiar to users is a hybrid one, with buttons. In fact, its functionality is not much wider than mechanical adjustment.
The touchpad, in most cases, is no different in principle from buttons. It is simply more reliable and requires no maintenance. Advanced electronic control circuits include programming, that is, switching according to a given algorithm of the radiation power and the time of its output.
Voltage conversion system
The microwave consists of a group of components that are very dangerous for humans. The main one is the step-up transformer. When the control circuit commands the mode to turn on, it produces up to 4 kV voltage. In this case, the operating current can reach 10A and higher. Such parameters of the electrical network pose a huge danger to humans.
Important! The step-up transformer is the key and most expensive component of the voltage conversion system. It powers the magnetron, an element without which it is impossible to implement the basic principle of operation of a microwave oven.
Microwave radiation generation unit
The magnetron is the heart of the microwave. In fact, this is an ordinary vacuum tube, similar to those that were used in picture tubes of old televisions. Only the magnetron generates an intense, high-frequency electromagnetic wave produced when electrons pass through a magnetic field.
The radiation generation unit consists of more than one microwave source. To, so to speak, supply waves to the working area of the furnace, waveguides are installed. They are the ones behind the mica plate that everyone saw on the side wall of the microwave when they put a plate of breakfast in it.
Primary and secondary protection systems
The role of control sensors is quite clear. They make sure that none of the key electronics and hardware elements reach critical operating conditions. Sensors guarantee trouble-free operation of the device and prevent dangerous malfunctions. But microwave ovens have safety systems designed for humans. Their functions will be described in detail below.
So, the control system initiates the start of the magnetron. It also sets operating parameters, counts time intervals, changes power, and so on. There is also feedback between the security and control systems. Based on the signals of the former, the operation of the furnace can be completely stopped, the mode can be changed, a service message or sound alerts can be issued.
Safety regulations
When using and repairing any household appliances, you must follow safety rules. Violating them can not only damage the device, but also harm human health or life.
Using a microwave oven correctly is easy:
- If the door is open, the oven cannot be turned on. This may occur if the waveguide or door locking system is damaged.
- You cannot connect a removed magnetron, it is dangerous to life.
- Do not operate the oven with a broken fan, otherwise it will lead to damage to the magnetron.
- Any actions with microwave parts are permissible only after disconnecting from the network and completely forcibly discharging the high-voltage capacitor.
- When the repair is completed, all objects must be removed from the waveguide, regardless of their size.
- Do not turn on the oven without load. If you need to run it in idle mode, then you must supply some food. It can be replaced with a container of water.
When disassembling, you should take photographs of each step. If problems arise with assembly, you can use the existing photographs. It is advisable to capture the original position and fastening of all parts using mobile phones or digital cameras.
Microwave wave distribution schemes
First, it’s worth focusing on the operation of the microwave generation unit. The structure of the magnetron consists of a radiating element and a winding that generates a magnetic field. This lamp, roughly speaking, is constantly wearing out. Everyone has encountered a situation where, as use progresses, the microwave heats up less and less. This is a normal phenomenon; every model sooner or later requires replacement of the magnetron.
Furnaces from different manufacturers (or levels of complexity) may use different microwave wave distribution schemes. In the standard solution used by LG and many other manufacturers, only one waveguide goes from the magnetron to the product area. It is covered with a mica plate to prevent debris and steam from entering.
Important! Models with a single waveguide, which emits a fairly localized stream of waves, use a reflector on the opposite side of the product compartment. This is the concave zone of the wall. It helps distribute microwave radiation more evenly throughout the working volume.
Some Samsung microwaves use a different principle: a main waveguide and several slot antennas are installed. This allows you to evenly distribute the energy flow, forming so-called 3D radiation. In addition, the oven, by varying the power of the magnetron, achieves smooth heating of the products throughout the entire volume.
But the most important thing in generating microwave waves is their parameters. The radiation frequency of the magnetron in the microwave is 2.45 GHz - this is the value that is resonant for water molecules, causing them to vibrate with a large amplitude. The product is heated. Heat from the surface layers gradually spreads throughout the entire volume of the product.
There are some solutions to speed up the heating of food in the oven work area. These are the so-called dissectors. In appearance, such a structural element is similar to a fan on the ceiling of a microwave oven. However, it does another job, namely, it scatters microwave waves.
Other functional elements of the furnace have a completely understandable purpose. For example, a microwave oven with a grill affects food not only with microwave radiation, but also with infrared radiation. It allows you to achieve a beautiful baked crust on your food. Some stove models can be equipped with additional fans to remove heat.
Possible causes of malfunctions
Problems begin due to neglect of operating rules. A microwave oven is a complex device, during operation of which energy is released and parts are heated.
The following cases are not allowed:
Metal objects in the chamber can cause damage to the magnetron; once it fails, it will be impossible to heat up food.
Containers with a lid for storing and heating food should be equipped with a “valve” in the upper part - a window, thanks to which excess pressure that appears during heating will be released. If it is not there, then the lid must be opened slightly. Otherwise, during heating, the food will be thrown out under pressure. This may also cause malfunctions.
Simple problems
The causes of some malfunctions can be detected simply by inspecting the microwave itself and the network cable. Over time, the stranded wire could break, the plug pins could melt or oxidize. In this case, the stove will not work, but sometimes there is enough voltage to operate the electric motor that rotates the plate, but there is no longer enough voltage to heat the food.
What to do if the wire or plug is faulty:
Be sure to check if the microwave works if you connect it to a different outlet.
Be sure to check the voltage at the outlet. If the settings are too low, the microwave will also operate partially. To correct the defect, you will have to contact the utility services; a technician must come and determine the cause of the excessively low voltage in the house or apartment.
Complex problems and case opening
If you still cannot determine the cause of the breakdown, you can either take the device to a service workshop or try to fix the defects yourself. To do this, you need to remove the cover (casing) by unscrewing the fastening screws.
Torsunov Pavel Maksimovich
If the device is under warranty, it is recommended to contact a service center. Otherwise, in case of unauthorized repair, the possibility of free repair within the specified period is canceled.
After removing the casing, you can see in the compartment:
The inspection must begin with the wires that connect the elements. If any wire is loose, you should determine which electrical appliance it went to and solder it in place. At the same time, you need to check the fuses. It is advisable to “ring” them using a tester to make sure they are working properly.
Defective fuses are replaced with new ones or a steel hair is soldered in place if the element is open.
Inexpensive models can be produced without fuses. When voltage drops in this case or short circuits occur, the magnetron most often suffers.
The magnetron consists of:
The antenna is a pin that comes out of the housing in the form of a small cylindrical terminal. If the cap (outer part) is blackened or plaque appears, then it is necessary to clean the surfaces using the finest sandpaper.
It is advisable to achieve a mirror shine. To do this, you may need a piece of felt (for polishing) and Goya paste or lapping compounds for valves from a car store. After work, you must remove all dust from the case using a vacuum cleaner.
If the antenna or housing is melted, then the entire magnetron must be replaced, and if its cost is too high, then it is easier to buy a new microwave.
On the camera side, the waveguide output is covered with a rectangular mica plate. Often, a microwave does not heat food because a layer of soot has formed on its surface and the waves from the magnetron simply cannot penetrate this obstacle.
In some cases, due to such a defect, sparks may appear during operation and smoke may come from the working chamber. There may be an unpleasant odor.
The plate can be easily removed:
How do you solve problems with technology?
If there are holes, the entire plate must be replaced. You can buy it in special stores that sell spare parts for household appliances.
If the microwave works but does not heat, then the problem may be in the condenser. They need to be checked manually. Capacitor - using an ohmmeter (tester). If the dial or display of the device shows some small resistance or nothing at all, then the capacitor is faulty. If excellent conductivity is visible, then everything is in order.
Torsunov Pavel Maksimovich
In rare cases, during long-term operation, one of the transformer windings may burn out. Most often this can be seen with the naked eye. Damage will be observed on the outside of the transformer.
How the protection system works
It is also worth covering in detail the functioning of security systems. They are divided into two significant groups.
- Monitoring hardware parameters. These are the magnetron temperature sensor, fuses, cooling fans. They solve the problem of blocking potential emergency situations and maintaining normal electronic performance indicators
- Protection of humans from electric shock and microwave radiation.
Anyone who has ever disassembled the body of their microwave has encountered electric shock protection systems. Microswitches are located at key installation points. Once the lid is removed, the stove can no longer be turned on. The security system simply will not allow this.
But more interesting is the scheme for neutralizing microwave waves. It is worth understanding that radiation, even theoretically, cannot be localized inside the furnace chamber. Waves are reflected, including from products. Therefore, glass with a thin metal grille applied to it is installed on the front door. This is an antenna module. It is connected to a spark gap, which releases the accumulated energy by surges into the main electrical network of the device.
Important! The microwave generates wiring noise. In some homes, this can be detected by the operation of other devices (in particular, Wi-Fi routers), especially if a frankly cheap stove with poor noise reduction is used.
Microwave electrical circuit
Based on the above, it is not difficult to understand how a microwave oven works simply by looking at it from the outside, looking into the chamber and at the rear. But if you want to fix something, it is useful to understand in general terms how the nodes interact with each other. A schematic diagram of a microwave oven will help with this. Its structure seems complicated only at first glance. However, any circuit consists of basic blocks. As an example, it is worth looking at the device of a model with mechanical analog control.
The diagram clearly shows how energy is converted and security systems operate. One of the very first circuits is always the noise suppressor (NOISE FILTER). It is this that dampens the vibrations generated by the energy discharger in the door, protecting people from high-frequency radiation.
Next comes the main security system. This is a block of contacts in the door, one monitors the fit to the body, the second the position of the latch, the third the position of the handle. If any of them is open, the oven will not work.
The third functional block is drives and lighting. Everything is simple here. A constant voltage is supplied to the motor that rotates the plate, the fan and the lamp. The timer opens the circuit when the set time interval ends.
The last operating circuit is a step-up transformer, a magnetron temperature control sensor, its breakdown protection system and a fuse. And the scheme always ends the same way. The main working part of the furnace is the magnetron.
Preparatory stage of repair: what is important to do before disassembling the microwave oven housing
After the safety briefing, we do the following:
- preparation of the workplace and tools;
- studying technical documentation;
- external inspection of the equipment being repaired.
The first question should not cause difficulties: I’ll omit it. But there may be problems with technical documentation. Therefore, I made a couple of simple diagrams that will allow you to understand the principles:
- operation of kinematic units;
- building electrical connections.
How does the mechanics of a microwave oven work?
High-frequency radiation is directed in one direction, but is reflected inside the cooking chamber. It creates local heating of individual areas of food. To increase the volume of the heated area, a rotating table is used, driven by its own electric motor with a drive.
The magnetron emitter is cooled by its own fan. The door curtains ensure smooth movement, and the latches clearly fix the closed position, controlled by limit switches.
What does the electrical circuit of a microwave oven consist of?
Here you need to clearly understand that a microwave oven can be controlled:
- digital technologies;
- or through the use of electromechanical devices.
Each option has different schemes with specific features. Therefore, for repairs, it is advisable to find an exact technical description from the manufacturer, which is quite difficult.
I’m showing a simple electrical diagram that allows you to understand the operating algorithms of such devices.
It includes:
- a high-frequency filter, which is designed to exclude the output of microwave pulses into household wiring and/or smooth out incoming interference;
- control module connected by microswitches with a programmer and buttons. It operates from a relay or microprocessor-based pulse shaping device;
- a high-voltage transformer with windings connected to a voltage multiplier and a cathode heating circuit;
- the magnetron itself, which produces electromagnetic waves in the microwave range.
What to look for when inspecting the stove externally
Before disassembling the case, it is necessary to evaluate:
- whether power supply is supplied to the internal circuitry;
- how reliably the door curtains and door locks work;
- Do the locking contacts switch clearly;
- smooth rotation of the table tray and the condition of its drive;
- backlight operation;
- the state of cleanliness of the waveguide window, as well as the internal walls of the cooking chamber.
When disassembling the case and removing the doors, be sure to photograph all components and mechanisms in their original and dismantled state. These pictures will greatly facilitate the subsequent assembly process.
Further, if we could not find a specific circuit from the manufacturer, we will rely on intuitive thinking and common sense.
