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Is your TV, radio, mobile phone or kettle broken? And you want to create a new topic about this in this forum?
First of all, think about this: imagine that your father / son / brother has an appendicitis pain and you know from the symptoms that it is just appendicitis, but there is no experience of cutting it out, as well as the tool. And you turn on your computer, access the Internet on a medical site with the question: "Help to cut out appendicitis." Do you understand the absurdity of the whole situation? Even if they answer you, it is worth considering factors such as the patient's diabetes, allergies to anesthesia and other medical nuances. I think no one does this in real life and will risk trusting the life of their loved ones with advice from the Internet.
The same is in the repair of radio equipment, although of course these are all the material benefits of modern civilization and in case of unsuccessful repairs, you can always buy a new LCD TV, cell phone, iPAD or computer. And for the repair of such equipment, at least it is necessary to have the appropriate measuring (oscilloscope, multimeter, generator, etc.) and soldering equipment (hairdryer, SMD-hot tweezers, etc.), a schematic diagram, not to mention the necessary knowledge and repair experience.
Let's consider a situation if you are a beginner / advanced radio amateur soldering all sorts of electronic gizmos and having some of the necessary tools. You create an appropriate thread on the repair forum with a short description of “patient symptoms”, ie. for example “Samsung LE40R81B TV does not turn on”.So what? Yes, there can be a lot of reasons for not switching on - from malfunctions in the power system, problems with the processor or flashing firmware in the EEPROM memory.
The purpose of this post is not any PR of repair shops, but I want to convey to you that sometimes self-repair can be more expensive than taking it to a professional workshop. Although, of course, this is your money and what is better or more risky is up to you.
If you nevertheless decide that you are able to independently repair the radio equipment, then when creating a post, be sure to indicate the full name of the device, modification, year of manufacture, country of origin and other detailed information. If there is a diagram, then attach it to the post or give a link to the source. Write down how long the symptoms have been manifesting, whether there were surges in the supply voltage network, whether there was a repair before that, what was done, what was checked, voltage measurements, oscillograms, etc. From a photo of a motherboard, as a rule, there is little sense, from a photo of a motherboard taken on a mobile phone there is no sense at all. Telepaths live in other forums.
The format of your post should be as follows:
Topics with the title “Help fix the Sony TV” with the content “broken” and a couple of blurred photos of the unscrewed back cover, taken with the 7th iPhone, at night, with a resolution of 8000x6000 pixels are immediately deleted. The more information you post about the breakdown, the more chances you will get a competent answer. Understand that the forum is a system of gratuitous mutual assistance in solving problems and if you are dismissive of writing your post and do not follow the above tips, then the answers to it will be appropriate, if anyone wants to answer at all. Also note that no one should answer instantly or within a day, say, no need to write after 2 hours “That no one can help”, etc. In this case, the topic will be deleted immediately.
If you decide to take your broken equipment to the nearest workshop, but do not know where, then perhaps our online cartographic service will help you: workshops on the map (on the left, press all buttons except “Workshops”). You can leave and view user reviews for workshops.
For repairmen and workshops: you can add your services to the map. Find your object on the map from the satellite and click on it with the left mouse button. In the field “Object type:” do not forget to change to “Equipment repair”. Adding is absolutely free! All objects are checked and moderated. A discussion of the service is here.
The main detail in any microwave oven is the magnetron. A magnetron is a special vacuum tube that generates microwave radiation.Microwave radiation has a very interesting effect on ordinary water, which is found in any food.
When irradiated with 2.45 GHz electromagnetic waves, water molecules begin to vibrate. Friction arises as a result of these vibrations. Yes, normal friction between molecules. Heat is generated by friction. It then heats up the food from the inside. This is how you can briefly explain the principle of the microwave oven.
Structurally, a microwave oven consists of a metal chamber in which food is cooked. The chamber is equipped with a door that prevents radiation from escaping. For uniform heating of food, a rotating table is installed inside the chamber, which is driven by a motor-reducer (motor), which is abbreviated as T.T.Motor (Turntable motor ).
Microwave radiation is generated by a magnetron and fed into the chamber through a rectangular waveguide. A fan is used to cool the magnetron during operation. F.M (Fan motor ), which drives cold air through the magnetron. Then the heated air from the magnetron is directed to the chamber through the air duct and is also used to heat food. Part of the heated air and water vapor is discharged outside through special non-radiating openings.
In some models of microwave ovens, a dissector is used to form an even heating of food, which is installed at the top of the microwave chamber. Outwardly, the dissector resembles a fan, but it is designed to create a certain type of microwave wave in the chamber so that uniform heating of food is carried out.
Let's take a look at a simplified electrical diagram of an ordinary microwave (click to enlarge).
As you can see, the circuit consists of a control part and an executive part. The control part, as a rule, consists of a microcontroller, a display, a push-button or touch panel, electromagnetic relays, and a buzzer. These are the “brains” of the microwave. On the diagram, all this is shown as a separate board with the inscription Power and Control Curcuit Board
The microcontroller controls electromagnetic relays through buffer elements (transistors): RELAY1 , RELAY2 , RELAY3 ... They turn on / off the executive elements of the microwave oven in accordance with the specified operation algorithm.
Actuators and circuits are a magnetron (Magnetron), a stage gear motor T.T.Motor (Turntable motor), a cooling fan F.M (Fan Motor ), Grill heating element (Grill heater ), backlight O.L (Oven lamp ).
We especially note the executive circuit, which is a microwave radiation generator.
This circuit begins with a high-voltage transformer (H.V.Transformer
An alternating voltage of 220V is supplied to the primary winding of the transformer. An alternating heating voltage of 3.15V is removed from one of the secondary windings. It is fed to the filament winding of the magnetron. Filament winding is necessary for the generation (emission) of electrons. It is worth noting that the current consumed by this winding can be up to 10A.
Another secondary winding of the high-voltage transformer, as well as the voltage doubling circuit on the high-voltage capacitor (H.V. Capacitor H.V. Diode 4kV for feeding the anode of the magnetron. The anode current is small and is somewhere around 300 mA (0.3A).
As a result, the electrons emitted by the filament winding begin to move in a vacuum.
The special trajectory of the movement of electrons inside the magnetron creates microwave radiation, which we need to heat food. Microwave radiation is removed from the magnetron using an antenna and enters the chamber through a section of a rectangular waveguide.
Here is such a simple, but very sophisticated circuit is a kind of microwave heater. Do not forget that the microwave oven chamber itself is an element of this microwave heater, since it is, in fact, a resonator in which electromagnetic radiation occurs.
In addition to these elements, there are many protective elements in the microwave oven circuit (see KSD thermal switches and analogs.). For example, a thermal switch monitors the temperature of the magnetron. Its nominal temperature during operation is somewhere between 80 0 - 100 0 C. This thermal switch is attached to the magnetron. By default, it is not shown in the simplified diagram.
Other protective thermal switches are labeled on the diagram as OVEN THERMAL CUT-OUT (installed on the duct), GRILL THERMAL CUT-OUT (controls the grill temperature).
In the event of an abnormal situation and overheating of the magnetron, the thermal switch opens the circuit, and the magnetron stops working. In this case, the thermal switch is selected with a small margin - for a shutdown temperature of 120 - 145 0 С.
Very important elements of the microwave oven are three switches, which are built into the right end of the microwave oven chamber. When the front door is closed, the two switches close their contacts (PRIMARY SWITCH - main switch, SECONDARY SWITCH - secondary switch). Third - MONITOR SWITCH (control switch) - opens its contacts when the door is closed.
Failure of at least one of these switches will cause the microwave to malfunction and trip the fuse (Fuse).
To reduce the interference that enters the power grid when the microwave oven is operating, there is a power filter - NOISE FILTER .
In addition to the basic structural elements, the microwave oven can be equipped with a grill and convector. The grill can be made in the form of a heating element (heating element) or infrared quartz lamps. These microwave elements are very reliable and rarely fail.
Grill heating elements: metal-ceramic (left) and infrared (right).
The infrared heater consists of 2 infrared quartz lamps connected in series at 115V (500 - 600W).
Unlike microwave heating, which comes from the inside, the grill creates heat radiation that heats the food from the outside to the inside. The grill reheats food more slowly, but without it, it is impossible to cook roasted chicken.
A convector is nothing more than a fan inside the chamber, which works in tandem with a heater (heating element). The rotation of the fan circulates hot air in the chamber, which contributes to uniform heating of food.
Elements in the magnetron power circuit have interesting properties that must be taken into account when repairing a microwave.
So, by default, the high-voltage capacitor (H.V. Capacitor ) has a built-in resistor.
It serves to discharge the capacitor. The fact is that the capacitor is under high voltage (2 kV), and therefore, after turning off the microwave oven, its discharge is required. This is a precautionary measure ... It also happens that the resistor inside the capacitor burns out and the capacitor does not discharge. Therefore, before repairing the microwave, it is recommended to forcibly discharge the capacitor onto the case.
Appearance of high voltage capacitor 1.0µF * 2100V AC.
High voltage diode (H.V. Diode ) is a combined element and consists of a whole string of diodes connected in series. This allows the composite diode to operate at high voltage. But this is the catch. The fact is that it will not be possible to test such a diode with a standard test method. The multimeter simply cannot “open” such a diode due to the fact that the threshold (forward) triggering voltage (VF ) diodes are added. As a result, the high voltage diode will have high resistance in forward and reverse connection.
So, for example, for the HVR-1X3 diode, the maximum forward voltage (VF ) is 11V. Considering that usually the voltage drop at the junction in direct connection (VF ) for silicon diodes is 1 - 1.1V, it turns out that 10 diodes connected in series are approximately mounted in the HVR-1X3 diode.
The maximum constant reverse voltage of such a diode is 12kV!
In some microwave ovens, parallel to the high-voltage capacitor is installed fuse diode (protective diode). Basically, a fuse diode is a bi-directional high voltage suppressor. It serves to protect the capacitor from an overestimated operating voltage, which is fraught with the failure of the latter. But in practice, it often happens that he himself fails. In such a case, the repairmen simply remove it from the chain like an unnecessary appendix. In fact, it turned out that microwaves work fine without such a diode.
For those who wish to understand in more detail the structure of microwave ovens, an archive with service instructions for microwave ovens has been prepared (Daewoo, SANYO, Samsung, LG). The instructions contain schematic diagrams, disassembly diagrams, recommendations for checking elements, a list of components.
We also recommend that you read the book "Microwave Oven Repair".
To repair a microwave oven, you need to have a general idea of how it works. Microwave oven repair begins with removing the top cover. Before that, you should take care of completely disconnecting the device from the power supply, only then proceed with the elimination of breakdowns with your own hands.
When these steps are successfully completed, a transformer with two fuses will open for access: one is located directly on the part itself, it is fusible, the second is located nearby on the very body of the microwave oven, made of ceramics. Also next to the transformer is a doubler block consisting of a thick capacitor and a diode. The whole set of these elements is the power supply circuit of the microwave oven magnetron.
Carefully! Do not touch the condenser immediately after removing the top cover. This element is capable of holding voltage for a long time, which can easily lead to an electric shock. When repairing a microwave oven with your own hands, this factor should be taken into account.
The peculiarity of microwave ovens is that all parts are connected in series. First, you should pay attention to the above magnetron and its power supply circuit. After removing the protective housing, a transformer with a large capacitor located next to it becomes accessible. There will also be a ceramic, low-melting fuse, a diode. The magnetron operates according to this high voltage circuit. Under no circumstances should you get into it with your hands, tools. After a complete de-energization, the capacitor will lose its residual voltage, the likelihood of an electric shock will decrease.
The primary winding of the micro-transformer takes over 220V. As a rule, its location is at the bottom. You can recognize it by the coils of copper wire, which will be bare in appearance. However, it is not. It is covered with a transparent insulating film. The location of this coil is under the secondary winding.
The microwave oven has two secondary windings. On one of them, several turns of a simple wire are usually not neatly wound. This heats up the cathode. Here the AC voltage is only 6.2V so that the electrons can be lifted from the surface. But where there is good insulation, there is a high voltage winding. About two kV directed towards the exit.
A capacitor shunted by a diode is located at the output of the circuit. The action of the negative half-wave falls on the cathode, the action of the positive half-wave charges the capacitance. Further, the electrode is subjected to double voltage, which is removed from the capacitor and the micro-transformer. As a result, approximately 3.5-4 kV is created. This power is enough to start the generation process.
You should be extremely careful, the output winding is always parallel to the magnetron, which has two output options. But the grounding of the anode is done in a separate way.
Thus, this is what happens:
the heating coil has 6.3V;
at the cathode stays up to 4.2 kV, grounded by the anode.
All microwave ovens have an electrical connection for the cathode, heating coil. Each microwave oven is equipped with a timer that controls the magnetron power. The use of a start relay is used in order to avoid the occurrence of a spark. Next, you should pay attention to the front panel.
The most likely breakages occur in the area of the mica plate. Energy is supplied from the magnetron to the waveguide along the rod. The latter is highly sensitive to the presence of various food debris. All these contaminants begin to ignite, emit sparks, thereby disrupting the stable operation of microwave ovens. To avoid unforeseen situations, the developers decided to close the waveguide with a mica plate. It has soft, flexible properties, relatively affordable pricing. It will not be difficult to fix such a breakdown with your own hands. You can buy material of any size, cut the corresponding segment. The peculiarity of the mica plate is that it transmits a frequency level of 2.45 GHz without obstacles. It is at this frequency that the microwave oven operates.
Also, mica plates do not get wet. This is a very important factor if liquid is heated inside microwave ovens. After all, water very quickly absorbs the radiating frequency of 2.45 GHz, there is a danger of serious damage. If the water reaches the waveguide, a big accident is created, which will not be easy to repair with your own hands. The high-voltage fuse will blow instantly. If things get worse, the magnetron itself burns out, other electronics that power the microwave oven.
What factors influence the destruction of the mica plate? Most reheated food contains a lot of fats, oils, and other such ingredients. They differ in that instead of the usual boil, they shoot out greasy drops. Once such a drop hits the mica plate, a small wire bridge is created. An electric arc is formed: from the waveguide to the mica plate, then from it to the body of the microwave oven. As soon as pops and sparks, uncharacteristic for the operation of stoves, appear, this is a sure sign that the stove will soon need to be repaired.
Anyone who has tried to fix the microwave with their own hands wondered about the high-voltage fuse. The mechanism of microwave ovens of this kind triggers at least two fuses:
If you look at the electronic board of the microwave, this part appears as a small white or transparent cylinder. Its task is to protect integrated, wall-mounted microwave oven components. This small cylinder is also part of the power supply circuit. Its burnout occurs in the event of a capacitor breakdown, a resistor short circuit.
The circuit that forms the power supply of the magnetron includes a diode, a transformer, and a capacitor. Through them, about two or three kilovolts approaches the cathode. These details are not difficult to find. It is difficult to confuse the appearance of the capacitor with anything else. This is a huge detail in the form of a jar weighing up to one hundred grams. One diode leg is attached to it, the other is fixed to the body. Nearby is also a small barrel, often ceramic, painted in brown. It is this barrel that contains a high-voltage fuse inside it. Its task is to prevent overheating of the magnetron. When a mica plate breaks through or a metal spoon is placed in the microwave oven, the high-voltage fuse immediately burns out.
VIDEO
It is best not to try to assemble the high voltage fuse with your own hands or remove it from the electronic board. This practice is extremely dangerous for people. The microwave oven may stop working and there is a high risk of fire and electric shock.
Before you start talking about repairing a fan that cools a magnetron, grills or an illuminating lamp in a microwave oven chamber, you should also pay attention to the protective relay. Their task is to turn off all operating systems at the moment when the chamber door is in the open position. Two relays usually break the power supply circuit. And one relay will be controlled by the functionality of the second. The work is carried out as follows:
If the oven door is open, the relay trigger is released.
In this operation, the power supply circuit has two breaks.
The second relay closes the ground on the phase.
When the first relay is energized, nothing bad will happen as the power supply circuit is in the open position.
When the first relay sticks, the fuse is blown out. This is due to the fact that the ground was short-circuited by a phase.
Video (click to play).
The fuse is not meant to be on top of the magnetron or inside the case, but on the board. To fix a microwave oven with your own hands, you should check the operation of the protective relay. Without this functionality, access to the power supply to the magnetron is practically impossible. The task of the power fuse is to take into account the movement of current in the magnetron. In the event of a dangerous situation, the protective element burns out, the generator breakdown is excluded. A similar situation occurs when the microwave oven is idle or there is some kind of metal thing in its chamber.
