The power supply has lost power repair. TV power supply repair

Malfunctions of modern switching power supplies

Often the causes of failures of pulsed voltage sources lie in poor-quality mains voltage. Lowering and increasing network voltage, power surges, and network shutdowns negatively affect the reliability of electronic components of power circuits.

Impulse power block

Such surges and network outages are especially painful for power diodes, powerful transistors, PWM controllers, and capacitors. It’s good when your voltage converter is made without filling with compound. You can do the repair of such switching power supplies yourself.

Increasingly, voltage sources filled with compound are appearing. They are not accepted for repair even in specialized workshops. For them, the only repair option is to replace it with a new one. Improper operation of these sources or connection of more powerful loads can also cause their failure.

There is no need to immediately send these converters for repair; the reasons for their failure can be quite simple, and you can easily deal with them. For more complex faults, some knowledge of electronics is required. Experience in repair comes with time, the more you do it, the more knowledge you will gain.

Diagnosis of faults in switching power supplies

The most important thing in repair is to find the fault, and fixing it is a matter of technique. The circuitry of switching power supplies can be divided into input and output parts. The input part includes a high-voltage circuit, and the output part has a low-voltage circuit.

In the high-voltage part of the board, all elements operate under high voltage, so they fail more often than elements in the low-voltage part. The high-voltage circuit has a network filter, diode bridges for rectifying the alternating voltage of the network, transistor switches and a pulse transformer.

Small isolating transformers are also used, which are controlled by PWM controllers and supply pulses to the gates of field-effect transistors. Thus, galvanic isolation of network and secondary voltages occurs. For such decoupling, optocouplers are often used in modern circuits.

Switching power supply circuit using transistors

The output voltages are also galvanically isolated from the network through a power transformer. In simple conversion circuits, instead of PWM controllers, self-generating transistors are used. These cheap voltage sources are used to power halogen lamps, LED lamps, etc.

The peculiarity of such schemes is simplicity and a minimum of elements. However, simple and cheap voltage sources do not start without a load, the output voltage is unstable and has increased ripple. Although these parameters do not affect the lighting of halogen lamps.

Diode bridge of ATX switching power supply

Repairing such a device is very simple due to the small number of elements. Most often, malfunctions occur in the high-voltage part of the circuit, when one or more diodes break down, electrolytic capacitors swell, and power transistors fail. The diodes of the low-voltage circuit also fail, the output filter inductors and the fuse blow out.

The malfunction of these elements can be detected with a multimeter. Other malfunctions of pulse units require the use of an oscilloscope or digital multimeter. In this case, it is better to send the unit to a workshop for repairs. The fuse can be easily tested with a multimeter for the presence of voltage after the fuse.

If a fuse has blown, you need to carefully visually check the entire circuit board circuit, tracks, soldering problems, darkening of circuit elements and sections of tracks, swelling of capacitors. If the diodes do not read well with a multimeter on the board, they are unsoldered and each one is checked separately.

All elements of the board are checked, the faulty one is replaced, and only then is the unit connected to the network for testing. During diagnostics, the capacitors are also unsoldered and checked with a tester. A burnt inductor can be rewound by determining the number of turns and wire cross-section. Finding the required throttle on sale will not be easy; it is better to restore it yourself.

Repair of UPS units of computers and televisions

To repair a pulse voltage source, you will need tools such as a soldering iron with temperature control, a set of screwdrivers, wire cutters, tweezers, a mounting knife, and a regular 100 W lamp. From the material you will need solder, flux, alcohol to remove rosin with a brush from the board solder. The equipment you will need is a multimeter.

Since switching power supplies (UPS) for televisions and computers have standard circuits, the method for detecting faults in them will be the same. A malfunction of the TV's voltage converter can be determined by the absence of LED backlighting.

The repair begins by checking the power cord, removing the power supply from the TV, and carefully inspecting the elements and traces of the board. They look for swollen capacitors, darkening of the tracks, cracked casing of alimony, charring of resistances, violation of the integrity of soldering joints, especially at the terminals of the pulse transformer.

If external damage is not found with a multimeter, check the fuse, diodes, power transistors of the keys, and the functionality of the capacitors. When you are sure that all elements are in good working order, but the device does not work, you need to change the pulse generator chip.

In a TV converter, the main faults occur in ballast resistors, low voltage electrolytic capacitors, and diodes. You can ring them without removing them from the boards (except for diodes). After troubleshooting, solder a 100 W lamp instead of the fuse and turn it on.

The lamp lights up and goes out, and the sleep mode LED lights up. The TV screen lights up. Then check the horizontal voltage; if it is higher than normal, change the capacitors.
The lamp lights up and goes out, but the LED does not light up, there is no raster. The reason is most likely in the pulse generator. Measure the voltage on the capacitor, which should be in the range of 280 - 300V. If the voltage is lower, the fault is sought in the diodes or in a capacitor leak. If there is no voltage on the capacitor, all circuits of high-voltage power supplies are checked again.
The lamp burns brightly when some elements are faulty. The voltage source is checked again.

Using an incandescent lamp, you can find possible faults in the source. To repair a computer's ATX source, you need to assemble a load circuit as in the figure below or connect it to a computer. However, if the malfunction of the ATX unit is not corrected, you can burn the motherboard.

An external manifestation of an ATX unit failure may be when the motherboard does not turn on, the fans do not work, or the unit tries to turn on repeatedly. Before troubleshooting the device, you need to clean it from dust with a vacuum cleaner and a brush. A visual inspection of the elements and board tracks is also carried out, and only after that the load is turned on.

If the fuse blows, then connect a 100 W incandescent lamp, as when checking the voltage source on a TV. When the lamp lights up but does not go out, the fault is looked for in the capacitor, transformer and bridge diodes. If the fuse is intact, a malfunction could occur in the PWM controller, then it is necessary to replace the device. Also, repeated starting of the source indicates a malfunction of the reference voltage stabilizer.

Safety precautions when repairing a switching power supply

The high side of the device does not have galvanic isolation from the network, so you should not touch the elements of this part with both hands. If touched with one hand, you will receive a noticeable electric shock, but it is not fatal. You cannot check live elements with a screwdriver or tweezers.

The high-voltage circuit of the device is indicated by a wide stripe, and the inside by small strokes of paint. The device has a high-voltage capacitor, which, after turning off the unit, holds dangerous voltage for up to 3 minutes. Therefore, after turning off, you need to wait until the capacitors are discharged or discharge them through a 3 - 5 Kom resistor. You can increase safety when repairing a device by using a safety transformer.

This transformer has two 220 V windings with a power of up to 200 W (depending on the power of the UPS). Such a transformer is galvanically isolated from the network. The primary winding of the transformer is connected to the network, and the secondary winding with the lamp is connected to the UPS. In this case, you can touch the elements of the high part of the device with one hand, you will not receive an electric shock.

How to repair and modify a Chinese-made 12-volt switching power supply

I want to start with the fact that I came into my hands with several burnt out and already “repaired” 220/12 V power supplies by someone. All the units were of the same type - HF55W-S-12, therefore, having entered the name in the search engine, I hoped to find a circuit . But apart from photographs of the appearance, parameters and prices for them, I found nothing. Therefore, I had to draw the circuit myself from the board. The diagram was drawn not to study the principle of operation of the power supply, but solely for repair purposes. Therefore, the network rectifier is not drawn, I also did not saw the pulse transformer and I do not know where the tap is made (start-end) on the 2nd winding of the transformer. Also, C14 -62 Ohm should not be considered a typo - there are markings on the board for an electrolytic capacitor (+ is shown in the diagram), but everywhere in its place there were resistors with a nominal value of 62 Ohms.

When repairing such devices, they need to be connected through a light bulb (100-200 W incandescent lamp, in series with the load), so that in the event of a short circuit in the load, the output transistor does not fail and the tracks on the board do not burn out. And your household will feel safer if the lights in the apartment don’t suddenly go out.
The main malfunction is the breakdown of Q1 (FJP5027 - 3 A, 800 V, 15 MHz) and, as a consequence, the breakage of resistors R9, R8 and the failure of Q2 (2SC2655 50 V\2 A 100 MHz). They are highlighted in color in the diagram. Q1 can be replaced with any transistor suitable for current and voltage. I installed BUT11, BU508. If the load power does not exceed 20 W, you can even install J1003, which can be found on the board from a burnt-out energy-saving lamp. One block was completely missing VD-01 (Schottky diode STPR1020CT -140 V\2x10 A), I installed MBR2545CT (45 V\30 A) instead, which is typical, it does not heat up at all at a load of 1.8 A (we used a 21 car lamp W\12 V). And within a minute of operation (without a radiator), the original diode heats up so much that it is impossible to touch it with your hand. I checked the current consumed by the device (with a 21 W lamp) with the original diode and with the MBR2545CT - the current (consumed from the network, I have a voltage of 230 V) dropped from 0.115 A to 0.11 A. The power decreased by 1.15 W, I believe that this is exactly how much was dissipated on the original diode.
There was nothing to replace Q2 with, so I found the C945 transistor at hand. I had to “power up” it with a circuit with a KT837 transistor (Figure 2). The current remained under control and when comparing the current with the native circuit on 2SC2655, there was an even reduction in power consumption with the same load at 1 W.

As a result, with a load of 21 W and when operating for 5 minutes, the output transistor and rectifier diode (without a radiator) heat up to 40 degrees (slightly warm). In the original version, after a minute of operation without a radiator, they could not be touched. The next step to increasing the reliability of blocks made according to this scheme is to replace the electrolytic capacitor C12 (prone to drying out of the electrolyte over time) with a conventional non-polar, non-electrolytic one. The same nominal value of 0.47 µF and a voltage of at least 50 V.
With such characteristics of the power supply, you can now safely connect LED strips without fear that the efficiency of the power supply will worsen the efficiency of LED lighting.

Any modern TV has a switching power supply.

A power supply is a whole unit designed to provide the TV with supply voltages of a certain power necessary for the normal functioning of the electrical appliance.

When the pulse unit is faulty, all sorts of problems with the television receiver are observed, including the fact that it does not work at all or stops turning on.

Possible power supply malfunctions

When VseRemont24 technicians come to a client’s home, they most often encounter a faulty power supply. This is the most common malfunction of televisions of all models, brands and types.

The power supply can be in the general circuit of the TV or in the form of a separate module.

Power supplies are unique in each TV, each has its own circuit. But their performance is equally negatively affected by:

violation by the owner of operating rules (especially temperature conditions),
relatively simple circuits,
unprofessional equipment repair.

Malfunctions typical for most power supplies:

Fuse blown.
The power supply does not start, there is voltage on the rectifier, the key elements are working.
The power supply does not start because the protection is triggered.
The power (key) transistor burns out.
Under- or over-voltage in primary or secondary circuits.

Obviously, only an experienced TV technician can figure out the breakdown and repair the TV. Self-repair is highly undesirable, however, it is possible.

Checking and repairing the power supply

If you have some experience, all the necessary knowledge and tools (in particular, a multimeter and a soldering iron), try to repair a television receiver.

Algorithm of actions when checking the TV power supply:

Turn off the TV (unplug from the socket).
Discharge the high voltage capacitor.
Remove the board from the TV case.
Inspect the board (visual diagnostics).
Check resistors, capacitors, diodes, transistors, etc. with a multimeter.
Inspect the back of the board. Check for cracks, gaps between tracks, and reliability of soldering of parts.

Resistors can:

darken
crack,
The quality of pin soldering deteriorates.

If all this is noticeable visually, it makes sense to replace the resistors with new ones with a deviation from the original of no more than plus or minus 5%.

If nothing is noticeable externally, you should check the resistors with a multimeter. The resistor is faulty if resistance = 0 or?.

Faulty electrolytic capacitors appear swollen. Their capacity is also checked. Permissible deviations are plus or minus 5%.

A working silicon diode has a resistance in the forward direction of 3-6 kOhm, and in the reverse direction - ?.

To measure resistance, you need to unsolder the diode. To check, set the multimeter to resistance measurement mode with a limit of 20 kOhm.

The second option is to check with a multimeter without soldering the diode. In this case, the multimeter must be set to the voltage drop measurement mode (should be up to 0.7 V). If the multimeter shows 0 or near zero, the diode will still have to be unsoldered and checked again. If the readings do not change, a breakthrough has probably occurred. A part needs to be replaced.

Bipolar transistors are tested in both directions (forward and reverse) at the transitions:

collector base,
base-emitter.

The test involves measuring the voltage drop in the transistors. It is also important to check that there is no breakdown in the collector-emitter junction.

Serviceable transistors behave like diodes, faulty ones need to be rechecked completely - the entire “piping”:

diodes,
resistors,
capacitors.

To check the supply voltage of a switching power supply, you will need:

his diagram
two incandescent lamps? 100W.

Algorithm of actions:

Using the diagram, find the output to the horizontal scanning stage.
Disable output.
Connect the incandescent lamp.
Connect the power supply through the second lamp.

If the lamp comes on and is bright, the power supply is faulty. If the light comes on and goes out or shines dimly, the input circuits of the power supply are working properly.

To determine which element is broken (which is why the light comes on), you need to refer to the diagram.

The test voltage measurement is carried out with a connected light bulb on the B+ load. The diagram shows what the voltage should be. Usually it is 110-150V. If it is correct, the power supply is working.

If the voltage is increased (200V), check the elements of the primary circuit of the power supply. If it is lowered - secondary circuits.

All faulty parts are soldered off and new ones are soldered in their place.

Remember! It is impossible to repair the TV power supply yourself without knowledge and experience. Even more important is that handicraft and amateur repairs are a direct threat to the health and even lives of people!

In modern consumer electronics, switching power supplies (UPS) are actively used. They are necessary to rectify and reduce the input voltage to a given value. Despite their fairly high reliability, UPSs can fail. If the user has some knowledge in the field of electronics, then he will be able to repair a 12-volt switching power supply himself.

Most power supply devices are based on standard circuits and have similar faults. If a person has at least basic knowledge in the field of electronics, then he can try to restore the UPS with his own hands. Since some parts of the power supply are live, even during initial inspection you must be careful.

In high-voltage UPSs, diode bridges are used to convert AC voltage to DC. The power supply also includes a smoothing capacitor. Since high voltage is converted into pulsed voltage with a frequency of 10 to 100 kHz, it has become possible to abandon the use of large step-down low-frequency transformers. Instead, pulse devices are now used, which are small in size.

In low-voltage UPSs, the voltage is first reduced to the required value, and then it is rectified, stabilized and smoothed. As a result, it is possible to obtain the voltage indicator that is necessary for the operation of the equipment. To increase the reliability of power devices and obtain stable output parameters, their design contains various control circuit solutions.

Please remember that not every power supply can be repaired. Today, many manufacturers produce electronic devices in which the units are subject to complete replacement. In them, printed circuit boards are often filled with a compound solution. In such a situation, even professionals do not undertake the restoration of the UPS.

The most common faults of switching power supplies most often caused by:

There are other possible reasons for the failure of this device, but they can only be detected by using special instruments, for example, an oscilloscope. In such a situation, high demands are placed on the technician repairing the device. If the cause of the UPS failure is not related to the four most common faults, then you should seek help from a professional.

Problems with the operation of the high-voltage section are quite easy to detect. To diagnose them, it is enough to check the voltage after the fuse. If there is input voltage in the low-voltage section, but there is no output voltage, then the cause of the malfunction must be looked for here.

If the fuse fails, you need to inspect the board. A burnt capacitor can be identified by swelling of its housing. To check the diode bridge installed in the high-voltage section, it is necessary to unsolder each component element, and then examine the device with a multimeter.

To exclude the possibility of a repeat malfunction after repair, you need to check all the parts. Having completed these works, you can proceed to checking the UPS. To identify a burnt-out inductor, you need to check the coils of all elements with a tester. If you cannot find the required replacement part, then you can rewind the burnt one yourself. However, this is a rather complicated process, so sometimes it is easier to buy a new power supply.

Restoring standard devices

Most often, attempts are made at home to restore power supplies for televisions and computers. It is advisable to first find a diagram of a specific device. First of all, this applies to TVs with picture tubes, since their UPSs produce a wide range of voltages. It’s easier with desktop PCs, because their power supplies are made according to a standard design.

Problems with the power supply are indicated by a non-working sleep mode LED. First you should check the functionality of the power cord. If no problem was found, then You can begin preliminary repair work:

If the visual inspection does not give positive results, then the fuse, diodes, capacitors and transistors are checked sequentially. It is quite difficult to establish the functionality of microcircuits.

Among the main malfunctions of TV power supplies you can note:

All these parts, except diodes, can be checked directly on the board. After replacing the faulty elements, a regular incandescent lamp is connected instead of the fuse, and the TV is connected to the network. Possible here the following behavior options for the restored unit:

The sleep mode LED turns on, and the lamp lights up and begins to fade. At the same time, a raster appears on the screen. In this case, it is necessary to check the horizontal scan voltage indicator. If its value turns out to be increased, then the reason may be faulty capacitors or optocouplers.
When the LED does not light up, there is no raster on the screen, and the lamp flashes and goes out, then the pulse generator is inoperative. In such a situation, you need to check the voltage on the capacitor. If its value turns out to be less than 280 V, then one of the bridge diodes may be broken or the capacitor may be damaged.
When the lamp lights up brightly, you need to check all the components of the UPS again.

This algorithm of actions will allow you to identify the main problems with the TV's power supply.

Desktop computer

It should be remembered that repairing switching power supplies with a PWM controller is difficult, so in some situations it is worth simply replacing the UPS. These are the power supply devices that are installed in modern desktop PCs. About the problem The following signs indicate:

To carry out repair work, it is necessary to remove the UPS from the system unit and remove the casing from it. Then you need to remove dust from the boards and parts using a brush. After this, a visual inspection of the block elements is carried out, then a load is connected to it. The algorithm for further actions is similar to TV repair.

If the pulse generator transistors or PWM controller fail, then you should just buy a new UPS. This is a rather complex device and it is difficult to repair switching power supplies of this type on your own.

When carrying out repair work, you must follow safety rules and exercise caution. It is also worth correctly assessing your capabilities, because sometimes it is better to turn to professionals.

Most modern household electronic equipment has in its design independent or located on a separate board electronic modules that reduce and rectify the mains voltage.

Moreover, for the last 20 years, instead of traditional buck-rectifier circuits based on a power transformer and a diode bridge, they have been built using a pulsed voltage conversion circuit. Despite their high circuit reliability, they often fail.

There are several reasons, but the main ones are:

mains voltage fluctuations for which these buck-rectifier devices are not designed;
non-compliance with operating rules;
connecting a load for which the devices are not designed.

Of course, it can be very frustrating when you need to do urgent work, but the computer’s power module is faulty or the device breaks down while watching your favorite TV show.

Do not immediately panic and contact a repair shop or rush to the electronics supermarket to purchase a new unit. Often the causes of inoperability are so trivial that they can be eliminated at home, with minimal expenditure of money and nerves.

General description of a household switching power supply device

Of course, in order to try not only to repair a switching power supply, but also to determine its malfunction, you must have basic knowledge of electronics and have certain electrical skills.

In addition, it should be remembered that some elements of the unit are under mains voltage, so even during the initial inspection of the device, care should be taken. However, most units are built according to standard circuits and have similar faults, so anyone can try to repair a switching power supply on their own.

Any power source, be it built-in, like in a TV, or installed as a separate device, like in a desktop computer, has two functional blocks - high-voltage and low-voltage.

In the high-voltage side, the mains voltage is converted by a diode bridge into constant voltage and smoothed out on a capacitor to a level of 300.0...310.0 volts. Constant, high voltage is converted into pulsed voltage, with a frequency of 10.0...100.0 kilohertz, which makes it possible to abandon massive low-frequency step-down transformers, replacing them with small-sized pulse ones.

In the low-voltage block, the pulse voltage is reduced to the required level, straightened, stabilized and smoothed. At the output of this block there is one or more voltages necessary to power household appliances. In addition, various control circuits are mounted in the low-voltage block to increase the reliability of the device and ensure the stability of output parameters.

Visually, on a real board, it is quite simple to distinguish between the high-voltage and low-voltage parts. The network wires come to the first one, and the power wires come from the second one.

Switching stabilizer in a transistor power supply

Diagnosis and simple repairs

A person planning to try to repair the power supply of household electronic equipment must be prepared in advance for the fact that not every power supply can be repaired. Today, some manufacturers produce electronics whose units are not subject to repair, but complete replacement.

No technician will undertake the repair of such a power supply, because it was originally intended for the complete dismantling of the old device and replacement with a new one. Often such electronic devices are simply filled with some kind of compound, which immediately removes the question of its maintainability.

Statistics show that the main malfunctions of the power supply are caused by:

malfunction of the high-voltage part (40.0%), which is expressed by breakdown (burnout) of the diode bridge and failure of the filter capacitor;
breakdown of a power field-effect or bipolar transistor (30.0%), which generates high-frequency pulses and is located in the high-voltage part;
breakdown of the diode bridge (15.0%) in the low-voltage part;
breakdown (burnout) of the output filter inductor windings.

In other cases, diagnosing is quite difficult and without special instruments (oscilloscope, digital voltmeter) it will not be possible. Therefore, if the malfunction of the power supply is not caused by the four above-mentioned main reasons, you should not engage in home repairs, but immediately call a specialist for replacement or purchase a new power supply.

Malfunctions of the high-voltage part are quite easy to detect. They are diagnosed by a blown fuse and no voltage after it. The third and fourth cases can be assumed if the fuse is working, the voltage at the input of the low-voltage unit is present, but the input is absent.

If the fuse blows, it is necessary to inspect the electronic board. A malfunction of the filter electrolytic capacitor is usually expressed by its swelling. To check the diodes of the high-voltage rectifier part, you will have to unsolder each of them (with a tester).

It is advisable to check all parts simultaneously. If several electronic elements burn out when replacing one of them with a working one, it may burn out again due to a complex malfunction that has not been eliminated.

After replacing parts, you must install a new fuse and turn on the power supply. As a rule, after this the power supply starts working.

If the fuse has not blown and there is no voltage at the output of the power supply, then the cause of the malfunction is a breakdown of the rectifier diodes of the low-voltage part, a burnt-out inductor, or the output of the electrolytic capacitors of the secondary rectifier unit.

The malfunction of capacitors is diagnosed when they swell or leak liquid from their housing. The diodes must be unsoldered and the high-voltage part must be checked in the same way. The integrity of the inductor winding is checked by a tester. All faulty parts must be replaced.

If you can’t find the right inductor, then some “craftsmen” rewind the burnt one, selecting a wire of a suitable diameter and determining the number of turns. Such work is quite painstaking and is usually performed only for unique power supplies; it is difficult to find an analogue for which.

Repair of standard devices

As already mentioned, most power supplies for modern computers and televisions are built according to a standard design. They differ in the sizes of the electronic parts used and the power output. The diagnostic and troubleshooting methods for these devices are identical.

However, high-quality repairs require appropriate tools, the range of which includes:

(preferably with adjustable power);
solder, flux, alcohol or purified gasoline (“Galosh”)
device for removing molten solder (de-soldering pump);
Screwdriver Set;
side cutters (nippers);
household multimeter (tester)
tweezers;
100.0 watt incandescent lamp (used as ballast load).

When starting to repair a television power supply or desktop computer system, it is advisable to have their electrical circuit diagram. Today this is not difficult to do - similar materials for most models of electronic equipment can be found on the Internet.

In principle, simple TVs can be repaired without a circuit, but the main difficulty in repairing some models is that the power supply produces the entire range of voltages - including the high voltage used to scan the kinescope. Power supplies for household computers are made according to the same type of design. Let's look separately at the method for identifying malfunctions and repairing a TV and desktop.

TV repair

A malfunction of the television power module is primarily indicated by the absence of light on the “sleep” mode diode. The first repair operations are:

checking for integrity (absence of break) of the power supply cord;
disassembling the television receiver and releasing the electronic board;
inspection of the power supply board for the presence of externally faulty parts (swollen capacitors, burnt spots on the printed circuit board, burst cases, charred surfaces of resistors);
checking soldering points, with special attention paid to soldering the contacts of the pulse transformer.

If it was not possible to visually identify the defective part, then it is necessary to sequentially check the functionality of the fuse, diodes, electrolytic capacitors and transistors. Unfortunately, if the control microcircuits fail, their malfunction can only be determined in an indirect way - when the power supply does not become operational even with fully operational discrete elements.

In repair practice, there are cases when the power module does not work (does not start) and the fuse is not blown. This may indicate a breakdown (burnout) of the high-frequency pulse generator transistor.

The most common reasons for television units not working are:

breakage of ballast resistances;
inoperability (short circuit) of the high-voltage filter capacitor;
malfunction of secondary voltage filter capacitors;
breakdown or burnout of rectifier diodes.

All these parts (except for the rectifier diodes) can be checked without removing them from the board. If it is possible to determine the faulty part, then it is replaced and they begin to check the repairs performed. To do this, install an incandescent lamp in place of the fuse and connect the device to the network.

There are several possible behavior options for the repaired device:

The light flashes and dims, the sleep mode LED lights up, and a raster appears on the screen. In this situation, the horizontal voltage is measured first. If its value is too high, it is necessary to check and replace the electrolytic capacitors with guaranteed serviceability. A similar situation occurs when optocoupler pairs malfunction.
If the light flashes and goes out, the LED does not light up, the raster is missing, which means the pulse generator does not start. In this case, the voltage level on the electrolytic capacitor of the high-voltage filter is checked. If it is below 280.0...300.0 volts, then the following malfunctions are most likely:
- one of the rectifier bridge diodes is broken;
- There is a large leakage of the capacitor (the capacitor is “aged”).
If there is no voltage, it is necessary to recheck the integrity of the power circuits and all diodes of the high voltage rectifier.
If the light glows strongly, you must immediately disconnect the power module from the network and recheck all electronic parts.

The above sequence and test diagram allow you to identify the main malfunctions of the power supply of the television receiver.

Desktop power supply repair

Today, the most widely used devices for powering desktop construction sets are “ATX” devices of varying power. The reason for their repair should be:

the motherboard does not start (the computer is completely inoperable);
the cooling fan of the device itself does not rotate;
the block repeatedly “attempts” to start itself.

Before starting repairs of ATX devices, it is necessary to assemble a load circuit (figure). Repairs are carried out in the following sequence:

the device is removed from the computer and the casing is removed from it;
use a vacuum cleaner and a brush to remove dust from electronic boards and surfaces of parts;
an external inspection of electronic elements and printed circuit boards is carried out;
load device is connected.

If there are no external signs of the cause of the malfunction, check the fuse. If it burns out, an incandescent lamp with a power of 100.0 watts is connected in its place (similar to repairing a television unit).

If, when turned on, the lamp flashes brightly and continues to burn, it means that the diode bridge in the high-voltage part or the filter capacitor has failed. The high-voltage transformer may burn out.

If the fuse is intact, then the cause of inoperability may be:

failure of the pulse generator transistors;
PWM controller malfunction.

In these cases, it is easier to purchase a new device, which, depending on the power, costs from 600...800 rubles.

When the device starts up repeatedly, the cause of inoperability is usually the failure of the reference voltage stabilizer. In this case, the computer system cannot pass the self-test mode and turns off and turns on the power module.