DIY TV power supply repair

In detail: DIY TV power supply repair from a real master for the site my.housecope.com.

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

There are several reasons for this, but the main ones are:

fluctuations in the mains voltage, for which these step-down rectifiers are not designed;
non-observance of operating rules;
connecting a load that the devices are not designed for.

Of course, it can be very annoying when urgent work needs to be done, and the power module of the computer is faulty, or while watching your favorite TV show, this device fails.

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

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

As part of any power supply, whether built-in, like in a TV or installed as a separate device, like in a desktop computer, there are two functional blocks - high-voltage and low-voltage.

In the high-voltage side, the mains voltage is converted by the diode bridge into a constant voltage, and smoothed on the capacitor to the level of 300.0 ... 310.0 volts. Constant, high voltage is converted into a pulse 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.

Video (click to play).

In the low-voltage unit, the impulse voltage is lowered to the required level, straightened, stabilized and smoothed out. At the output of this unit, there is one or more voltages required to power household appliances. In addition, various control circuits are mounted in the low-voltage unit, which make it possible to increase the reliability of the device and ensure the stability of the output parameters.

Visually, on a real board, it is quite easy to distinguish between high-voltage and low-voltage parts. The network wires are suitable for the first, and the supply wires go from the second.

Switching regulator in the transistor power supply

A person who is going to try to repair a power supply unit for household electronic appliances must be prepared in advance that not every power supply device can be repaired. Today, some manufacturers produce electronics, the blocks of which are not subject to repair, but to complete replacement.

Not a single master will undertake the repair of such a power supply unit, because initially it is intended for the complete dismantling of the old device with 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.

As statistics show, the main malfunctions of the power supply are caused by:

malfunction of the high-voltage part (40.0%), which are expressed by the breakdown (burnout) of the diode bridge and the failure of the filtering capacitor;
breakdown of a power field-effect or bipolar transistor (30.0%), which forms 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 choke windings of the output filter.

In other cases, the diagnosis is quite difficult and without special devices (oscilloscope, digital voltmeter) it will not be possible to perform it. 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 master for replacement or purchase a new power supply device.

Faults in the high-voltage section are easy enough to detect. They are diagnosed by a blown fuse and a lack of voltage after it. The third and fourth cases can be assumed if the fuse is good, the voltage at the input of the low-voltage unit is present, and the input voltage is absent.

It is advisable to check all the details at the same time. If several electronic elements are burned out, when one of them is replaced with a serviceable 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 begins to work.

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 the breakdown of the rectifier diodes of the low-voltage part, the burnout of the inductor or the output of the electrolytic capacitors of the secondary rectifier unit.

Malfunction of capacitors is diagnosed when they are swollen or fluid leaks out of their body. The diodes must be evaporated and checked with a tester in the same way as checking the high-voltage part. The integrity of the choke winding is checked by a tester. All defective parts must be replaced.

If you cannot find the desired choke, then some "craftsmen" rewind the burned-out one, picking up 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.

As already mentioned, most power supplies for modern computers and TVs are built according to a typical scheme. They differ in the size of the electronic parts used and in the output power. The diagnostics and troubleshooting procedures for these devices are identical.

However, a high-quality repair requires an appropriate tool, the range of which includes:

soldering iron (preferably with adjustable power);
solder, flux, alcohol or refined gasoline (Galosha);
device for removing molten solder (desoldering pump);
Screwdriver Set;
side cutters (nippers);
household multimeter (tester)
tweezers;
100.0 watt incandescent lamp (used as ballast load).

In principle, simple TVs can be repaired without a circuit, but the main difficulty in repairing some models is that the power supply device generates the entire range of voltages - including the high-voltage used to scan the kinescope. The power supplies for household computers are made according to the same type of scheme. Let us consider separately the methodology for determining the malfunction and repairing the TV and desktop.

A malfunction of the TV power module is first of all evidenced by the absence of a glow of the "sleep" mode diode. The first repair operations are:

check for the integrity (absence of breakage) of the supply voltage cord;
disassembly of the television receiver and release of 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 surface of resistors);
checking the soldering points, with special attention paid to soldering the contacts of the pulse transformer.

If it was not possible to visually establish the defective part, then it is necessary to sequentially check the performance of the fuse, diodes, electrolytic capacitors and transistors.Unfortunately, if the control microcircuits are out of order, their malfunction can be established only indirectly - when, with completely serviceable discrete elements, the operational state of the power supply does not occur.

The most common reasons for the inoperability of television units are:

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

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

Several options for the behavior of the repaired device are possible here:

The light flashes and goes out, the sleep mode LED lights up, a raster appears on the screen. In this situation, the line scan voltage is measured first. If its value is too high, it is necessary to check and replace electrolytic capacitors with guaranteed serviceable ones. A similar situation manifests itself in the event of a malfunction of the optocouplers.
If the lamp flashes and goes out, the LED does not light up, the raster is absent, then the pulse generator does not start. In this case, the voltage level on the electrolytic capacitor of the filter of the high-voltage part 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;
- large capacitor leakage (the capacitor is "old").

If there is no voltage, it is necessary to re-check the continuity of the supply circuits and all diodes of the high voltage rectifier.

If the light is high, you must immediately disconnect the power module from the network and re-check all electronic parts.

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

Today, ATX devices of various capacities are most widely used for powering desktop (desktop) designers. The reason for their repair should be:

the motherboard does not start (the computer is completely inoperative);
the cooling fan of the device itself does not rotate;
the block “tries” to start itself many times.

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

the device is removed from the computer and the cover is removed from it;
a vacuum cleaner and a brush removes dust from electronic boards and surfaces of parts;
external examination of electronic elements and printed circuit boards;
a load device is connected.

If, when turned on, the lamp flashes brightly and continues to burn, then the diode bridge in the high-voltage part or the filter capacitor is out of order. Burnout of the high-voltage transformer is possible.

If the fuse is intact, then the reason for inoperability may be:

failure of the transistors of the pulse generator;
malfunction of the PWM controller.

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

With repeated self-starting of the device, the reason for inoperability is usually the failure of the reference voltage stabilizer. In this case, the computer system cannot pass the self-test mode, it turns off and turns on the power module.

Typically, it takes much longer to diagnose a problem with a TV than it takes to fix the problem. Of course, you can always entrust this work to a professional, but in the end, the whole procedure will take even longer. Therefore, users often try to repair the TV's power supply with their own hands.Should I do it? How to proceed with self-repair? What nuances should you pay attention to in order to make sure that the power supply is faulty and not cause even more damage to the TV? You will find the answers to all these and many other questions in this material.

Unlike other TV components, any breakdown of the power supply immediately affects the performance of the TV as a whole. This means that after turning on the TV to the network, the activity indicator will not even light up, not to mention the output of sound, pictures or the manifestation of other signs of life. The manifestation of a breakdown can be as follows:

the TV does not turn on and the LED does not light up;
the device does not function due to the operation of the protection in the power supply, which is usually accompanied by the whistling of a pulse transformer. This manifestation may also indicate the necessary repair of LED backlighting in TV;
too low or excessively high output voltage comes from the power supply unit.

If the device can turn on and some defects simply appear in its operation, then this is most likely caused by another component of the TV, and not the power supply. However, there are also a number of exceptions in which the problem is still associated with the PSU:

the device does not turn on, although the standby LED is on;
the image appears some time after the sound;
to get a normal picture and sound, the TV must be turned on and off several times.

Separately, it is also worth mentioning possible breakdowns of other components of the TV, which are not caused by malfunctions of the power supply unit, but directly affect its operation. These include power-on nodes, feedback circuits, power supply loads, and so on.

Failure of the power supply is one of the most common breakdowns of modern LED TVs. The cause of this malfunction can be caused by many factors, but among them 4 main ones can be distinguished:

Unstable voltage... If the voltage in the outlet is constantly "jumping", then it can not only worsen the operation of the TV, but also lead to wear and tear of its components.
Short circuit... Causes the power supply unit or other TV components to burn out.
Blown mains fuse... In this case, the standby indicator will not light up.
Capacitor wear over time... A very common problem that does not depend on external factors. Worn capacitors can be identified by their swelling.

The first step is to disassemble the TV by removing the back cover of the device, which is fixed with screws around the perimeter. Depending on the model and manufacturer of your TV, you can access the PSU after this stage.

If you did not notice this part after removing the cover, then it is located under a protective metal casing. In some models, it is also possible to install another protection specifically for the power supply. At each stage, you will need to unscrew the screws in a circle that secure the component to be removed.

Before you start repairing the TV's power supply, you need to figure out what this component looks like. All modern models have several power supplies, but they are all located on one board. It is not at all difficult to distinguish it from others, because in addition to capacitors and other components, this board also contains three transformers (painted in black and yellow).

As for the components of the PSU, they are as follows:

Duty power supply... In order for the device to be in standby mode (LED is on) and wait for any command, it must receive a voltage of 5V. It is the power supply on duty that gives it to the TV.

Inverter unit... If the TV tries to turn on, but then immediately goes back to standby mode, then the problem is related to this part.It is responsible for supplying power to the corresponding component, therefore, in the absence of power, the processor cannot receive confirmation of operability from the inverter and changes to standby mode.

BlockPFC... Power is divided into active and reactive. The first one does useful work, while the reactive one simply goes from the generator to the load and vice versa. The second type can be inductive or, as is typical for TVs, capacitive (capacitors). Reactive power is needed for the TV to function, but it can significantly increase power consumption, as well as wear out capacitors faster, which negatively affects the durability of the PSU as a whole.

To exclude the indicated phenomena, a special PFC (Power Factor Correction) block is used, which, as its name suggests, deals with power factor correction.

The TV may not turn on due to unstable voltage, so this problem is solved with a stabilizer. Also, the reason is often the inoperability of an extension cord or outlet. Moreover, different power sources in the apartment can be connected to different machines in the dashboard, so the presence of light in the house does not mean that the outlet you need is supplied with electricity. If there are no problems with the power supply, then you need to ring the output of the standby power supply unit with the help of the tester.

As a result, you should get 5V, and if you get a value less or completely absent voltage, then the problem is worn out capacitors. They can be determined by visual inspection, because such components will be swollen.

In the same case, when a problem is not found here, it is necessary to check the fuse. To do this, you also need to ring it, checking if there is a short circuit somewhere. Additionally, you need to inspect the back of the board by removing it from the frame.

The first step is to discharge the input capacitors. If this is not done, then during the repair process, a short circuit or other problems may occur, which will lead to more serious damage. For discharging, you can use a low-resistance resistor, a tester or an ordinary light bulb, brought to the contacts for a few seconds. After that, you can dissolve the damaged capacitors and replace them with working ones with the same power.

Important! Any repair of a power supply is associated with a number of risks. If you act carelessly, you can cause even greater harm to the TV or even your own health. If you have any doubts about your own abilities, you should entrust the repair procedure to an experienced master.

A video lesson from the master will tell you in detail about the whole process of repairing a power supply unit:

TV power supply repair is one of the most popular workshop services. It is this component that is most often denied in modern TV. Faced with a similar situation, you can fix the problem yourself. Our detailed guide will help you with this, containing the necessary recommendations and explanations.The switching power supply is built into most household appliances. As practice shows, it is this unit that often fails, requiring replacement.The high voltage constantly passing through the power supply does not have the best effect on its elements. And it's not about the manufacturers' mistakes. By increasing the service life by mounting additional protection, you can achieve the reliability of the protected parts, but lose it on the newly installed ones. In addition, additional elements complicate the repair - it becomes difficult to understand all the intricacies of the resulting scheme.Manufacturers have solved this problem radically, reducing the cost of the UPS and making it monolithic, non-separable. Such disposable devices are becoming more common. But, if you are lucky - the collapsible unit has failed, self-repair is quite possible.The principle of operation is the same for all UPSs. The differences concern only schemes and types of parts. Therefore, it is quite simple to understand the breakdown, having basic knowledge of electrical engineering. Image - DIY TV power supply repair

You will need a voltmeter for repairs.

It measures the voltage across an electrolytic capacitor. It is highlighted in the photo. If the voltage is 300 V, the fuse is intact and all other related elements (power filter, power cable, input chokes) are in good order.

There are models with two small capacitors. In this case, the normal functioning of these elements is evidenced by a constant voltage of 150 V on each of the capacitors.

In the absence of voltage, you need to ring the diodes of the rectifier bridge, the capacitor, the fuse itself, and so on. The insidiousness of the fuses is that, having failed, they outwardly do not differ in any way from the working samples. The fault can only be detected through a dial tone - a blown fuse will show a high resistance.

Having found a faulty fuse, you should carefully inspect the board, since it often fails at the same time as other elements.

power or rectifier bridge (looks like a monolithic block or may consist of four diodes);
filter capacitor (looks like a large block or several blocks connected in parallel or in series) located in the high-voltage part of the block;
transistors installed on the radiator (these are field switches - power switches).

Important. All parts are soldered and replaced at the same time! Replacing in turn will lead to burnout of the power unit each time.

For certain purposes, a switching power supply can be assembled independently from scrap parts. Read more about this here.

Burnt-out elements must be replaced with new ones. The radio market offers a rich assortment of parts for power supplies. Finding good options at the lowest prices is pretty easy.

voltage drops;
lack of protection (there is space for it, but the element itself is not installed - this is how manufacturers save).

Solution this malfunction of switching power supplies:

install protection (it is not always possible to find the right part);
or use a mains voltage filter with good protective elements (no jumpers!).

Another common cause of a power supply malfunction has nothing to do with a fuse. We are talking about the absence of an output voltage with a fully functional such element.
Solution:

Swollen Condenser - Desoldering and replacement required.
Failed choke - it is necessary to remove the element and change the winding. The damaged wire is unwound. In this case, the turns are counted. Then a new wire of a suitable section is wound on the same number of turns. The part is returned to its place.
Deformed bridge diodes are replaced with new ones.
If necessary, the parts are checked with a tester (if no damage is detected visually).

It is quite possible to build a hot air soldering station yourself. A fan is used as a blower, and a spiral is used as a heater. The best option for a temperature controller for a soldering iron is a thyristor circuit.

Breakdown reasons:

do not block ventilation openings;
provide optimal temperature conditions - cooling and ventilation.

Things to Remember:

The first connection of the unit is made to a 25-watt lamp. This is especially important after replacing diodes or transistor! If a mistake is made somewhere or a malfunction is not noticed, the passing current will not damage the entire device as a whole.
When starting work, do not forget that a residual discharge remains on electrolytic capacitors for a long time. Before soldering the parts, it is necessary to short-circuit the capacitor leads. You cannot do this directly. It should be short-circuited through a resistance with a nominal value higher than 0.5 V.

Photo of the TV power supplyAmong all the malfunctions, the repair of power supplies takes the first place. In the article "TV Power Supply Malfunctions" I described typical power supply failures.In this article I want to describe the work and repair of power supplies in more detail.You probably need to start with how to check the power supply after repair, so as not to cause it to break again. Although this method is considered controversial, I find it very effective.So after repairing the power supply, you need to solder a 150 watt light bulb into the fuse break (it can be 100, but there may be a false glow), and solder the light bulb into the B + circuit break (line scan power 95-145 volts, you can simply cut the track) 40-60 watts. Please note that some power supplies will not start at light load.This system works like this. When you turn on the network after repairing the power supply, if it is working properly, the first light bulb at the moment of charging the network capacitor (100-220μF 450V) lights up and goes out as it charges. A weak glow remains. A 60-watt light bulb glows according to the voltage in the floor.With a faulty power supply, a 150 W lamp glows with full incandescence. In some cases, this saves the transistor, microcircuit from repeated failure of key elements.In the second method, the power transistor of the power supply is not soldered and the level and shape of the signal coming to it is analyzed with the help of instruments (oscilloscope, multimeter).In the description, I will rely on the diagram below. Image - DIY TV power supply repair

Malfunctions can be caused by:

We check for a short circuit the elements of the mains filter, rectifier, thermistor - demagnetization system, the key and its strapping elements, as well as the key microcircuit (if the power supply is built on it).
When you find a faulty element, analyze the reasons for its failure. Failure of the transistor can be caused both by a voltage surge in the network, and by drying out of capacitors in the primary circuits.

The power supply does not turn on, the mains fuse is intact.
It should be checked for breakage: mains filter, rectifier, PWM - modulator.
Start by checking if the mains capacitor C has a constant voltage of about 300V (if not, look for a break in the mains filter, and also check the resistor R.
If there is + 300V on the capacitor C, check if it reaches the key transistor. You should also check the primary winding of the TP mains pulse transformer for breakage.
If all the elements are in good working order, and the power supply does not turn on, it is necessary to check the arrival of pulses to the base (gate) of the transistor.
Also check the trigger R circuitry, usually high resistance resistors.

Check: the elements of the secondary rectifiers of the power supply, the loads of the power supply for a short circuit, the elements of the protection system (monitoring circuits for the output voltages), feedback circuits (modulator).
With the secondary circuits and their loads, I think everything is clear, it is necessary to check the rectifiers (diodes) and filter capacitors.
In the protection circuits, check the optocoupler and its piping.

With regards to the feedback circuits, check the zener diodes, diodes, capacitors (usually 4.7-10- 47 microfarads).

Network capacitor, capacitors of the PWM strapping, serviceability of the optocoupler and its strapping.

In this case, proceed as follows:

check the soldering of the power supply elements for ring cracks;
check the elements in the hottest places on the board by identifying them by blackening.
In the event that a malfunction manifests itself when the TV is warming up, it is possible to localize the defective element either by cooling (cotton wool soaked in acetone, alcohol), or to speed up the occurrence of a malfunction by provoking it by heating one or another element with a soldering iron.

Hello! Please help me choose an analogue power supply unit (Wene-wn220a-3 24V 7A) for the Chinese TV no. Found one similar to ebay, but I'm not sure about the insides. And what parameters should be used to select an analogue?

Two parameters are needed: 1) Voltage. Should be similar, in this case 24 V. 2) Amperes. In this case, 7 A.This parameter should be at least 7 amperes, but it should be borne in mind that the larger this number, the more expensive the power supply will be.

tel JVC-AVG14T. When turned on from standby mode, an image appears. and stars. and after 5 seconds everything goes out while the green LED blinks at a frequency of 1 time per second. and does not turn on anymore. It is necessary to turn off the PCN, then everything will be repeated. Changed all the electrolytes in the B / P, optocoupler, zener diode and transistors near it, help! THX.

It is necessary to check the diodes of the secondary circuits, horizontal scanning and vertical scanning.

help Blow fuses on TV Meredian Model TK-5411

The power supply does not start and the light diode does not tell where to look for the cause. Tv polar platform Т08-29к

Doesn't say anything, let's model.

Hello!
The power supply unit is assembled with a key on a composite field, a VESTEL VR2106TS TV, a chassis on an AK-36 tr-re, if I'm not mistaken. Symptoms of malfunction: short-term periodic start of the power supply unit (clatter), while, in time, a whistle is heard, the power-on indicator LED blinks red.
How would you start troubleshooting? With the search for a short circuit in the load of the tr-ra, or a malfunction in the piping of the shim controller?

I would start looking for a fault in the secondary power supply unit, line and personnel.

can parallel to the lamp be turned on on the tra-tor of the 2nd winding, having previously disconnected the sweep with the output stage and tdks?

Quite right. The light bulb is soldered to the plus of the capacitor 100 microfarads * 160v and the case (minus) of the chassis, track on a line or cut off the power or evaporate the transistor

In the power supply, the lamp 60-75 -95-150w lights up and immediately goes out, which means that the power supply is normal! (40w) I connected a light bulb in series from the trance, then the second end to the choke, those to the capacitor - maybe it is necessary, most likely after it (filter) I think that after the air conditioner am I right or not? thanks for the answer!

Hello! Tell me, after repairing the power supply, I put a light bulb in the break of the mains fuse and it began to start a horizontal scan, but intermittently (extinguished) the lamp and naturally when the start goes out! lamp 60 W and 100 I am afraid to put was a pre-incident burned already on another TV set a bunch of tr-ditch and micro-circuits! It makes no sense to put a lamp in a line of 60 W, because there is a launch - you can even hear it! thanks in advance!

In place of the fuse, a lamp of 150 - 200 W, in a line of 40 W. Most of the line transistors have Pout - 50 watts. Disconnect the line all the same and see if it turns off. If there is, then the problem is in the power supply, no, then in the line.

repair of the TV's power supply still takes second place after the line

A huge THANKS to the author for the material. 111

Guys, help me in short on the Odeon LTD-150D TV malfunctions in the power supply, it seems to me that the problem is in the transistor, tell me where to go with the question?

If there is no knowledge in electronics, then definitely go to the workshop.

Yes, at the expense of the capacitor, I agree, I got a good 400V in my little finger.

I checked all the elements are in good order and the voltages are still underestimated what else to check

Does winding 2 work for itself?

Winding 2 monitors the mains voltage and generates a feedback signal proportional to the secondary voltages.

When repairing the power supply, be sure to discharge the line capacitor. Its charge may damage or shock something.

A defective TV power supply is one of the frequent breakdowns. It is his task to provide power to all the nodes of the TV. Since electrical networks often have deviations from the norms, frequent outages and surges of electricity lead to failure of power supplies for TVs and other radio equipment, too.

Other reasons that make the power supply unusable:

the presence in power supplies of circuits, the elements of which are under the influence of impulse voltages and currents of large ratings (for voltage - up to 1000V, for current up to 5A);
the presence of a large number of heat-generating elements in the power supplies;
low technological quality of development and installation of electronic circuits (especially for FUNAI TVs);
malfunctions of electronic components (hidden factory defects);
operation of TVs in non-recommended climatic conditions, as well as using an AC mains with parameters different from the recommended ones.

Of course, in order to prevent possible malfunctions in the future, you just need to follow these rules:

when purchasing a TV, focus on a well-established manufacturer (Panasonic, Philips, Sony, etc.), and also opt for a basic TV model (for example, Sony 2100 or Toshiba 2135);
try to comply with the operating conditions of the TV specified in the operating instructions for the particular model.
Let's dwell on the most typical faults of power supplies:
the power supply does not work (options: when the mains fuse blows out and when it remains intact);
the protection of the power supply is triggered (often in this case, a high-pitched whistle or intermittent whistle is heard from the pulse transformer in the power supply);
the power supply unit gives out underestimated or overestimated values of output voltages;
so-called floating faults;
malfunctions of TV units that are not associated with defects in the power supply, but somehow affect its operation (feedback circuits of the power supply clocking from horizontal scanning, power supply loads, power-on nodes).

Let us dwell on these faults in more detail.

1. Mains fuse blows when power is turned on.

The following components may be the cause of this malfunction:

mains filter and rectifier;
unit for automatic switching of input voltage (110V - 220V);
key modulator elements;
demagnetization system.

To make sure that one of the above nodes is in good working order, you should turn them off one by one (which is the easiest way).

Disconnect the demagnetization system first. To do this, it is enough to evaporate the thermistor. This must be done because the twin thermistor - demagnetizing loop is connected in parallel with the supply network and in the cold state its resistance is small enough, which will interfere with the search for a faulty element with an ohmmeter. Also break the “+” circuit of the network diode bridge from the rest of the circuit and check in sequence:

short circuit power filter (see Fig. 13);

In this block, filter capacitors C, C1, C2 most often fail.

The current-limiting resistor R often burns out at the same time as the mains fuse F (if C, C1 are in good working order). The inductive filter T very rarely fails.

network rectifier for bridge diode breakdown;

a filtering capacitor after the diode bridge (it is large, with a capacity of 200-500 μF - for an operating voltage of 300-400V) for a short circuit;
elements of the key modulator (pay special attention to the serviceability of the powerful terminal transistor of the PWM modulator, the elements of its framing, as well as the key microcircuit (if any)).

When you find a faulty element, analyze the reasons for its failure. In some cases, the failure of one or more elements is the result of a failure of a completely different unit.

For example, failure of a powerful key transistor of a power supply can be initiated by faults in protection circuits, output voltage tracking circuits, pulse transformer, PWM modulator.

After finding the faulty element and replacing it, repair the broken circuits.

In the event that the automatic power switching unit is faulty, the following may fail: a mains fuse, a current-limiting resistor R (see Fig. 13), a rectifier, filtering electrolytic capacitors, as well as elements of a PWM modulator. This is a rather serious malfunction.And the reason for all this is either the controller of the mains voltage switch, or a powerful transistor (thyristor).

2. The power supply does not turn on, the mains fuse is intact.

In this case, you should also check the elements of the path:

mains filter - rectifier - PWM - modulator.

First, check if the mains electrolytic capacitor C has a constant voltage of about 300V (see fig. 14). If not, look for a break in the surge protector, and also check the resistor R (Fig. 13).

If there is + 300V on the capacitor C, turn off the power, discharge C and check the circuit from the diode bridge through the primary winding of the pulse transformer to the collector (or drain - in the case of using a field-effect transistor) of the switch transistor T (Fig. 14)

You should also check the windings of the TP mains pulse transformer for short-circuiting of the turns.

The following method of testing pulse power transformers for short-circuited turns has proven itself well: the parallel resonance method (Fig. 15).

Necessary equipment:

Low frequency generator (LFO).
Oscilloscope or high-frequency millivoltmeter (with the ability to measure in the frequency range of 10 - 200 kHz).

Principle of operation.

The principle of operation is based on the phenomenon of resonance. An increase (from 2 times or more) in the amplitude of oscillations from the low-frequency generator indicates that the frequency of the external generator corresponds to the frequency of the internal oscillations C * L * of the circuit.

To check, short-circuit the secondary winding L of the transformer. The oscillations in the C * L * circuit should disappear. It follows from this that short-circuited loops break the resonance phenomena in the C * L * circuit. The presence of short-circuited turns in the L * coil will also lead to a breakdown of resonance phenomena. It should be noted that this test method is effective if the ratio of the number of short-circuited turns to the number of turns of the primary winding should correlate (under different conditions) as: Wsc / W> (1/100: 1/10) (see Fig. 16).

If you did not find a faulty element in the primary power circuit, check sequentially: semiconductor elements (transistors, diodes, optocouplers, etc.), then electrolytic capacitors and all other elements, if the power supply contains integrated microcircuits, they should be " check "replacement.

It should be noted that burnt, charred elements, as well as electrolytic capacitors with a swollen notch (on top of the case) are subject to immediate replacement.

Necessarily analyze the reason for the failure of the found faulty element.

You should also check (in some types of power supplies) the operation of the standby power supply, which, in turn, feeds the circuits that control the switching on of the main power supply (usually through optocouplers or special circuits). Since the standby unit has a low-power power transformer and a parametric stabilizer, the repair of this unit does not cause problems.

3. Power supply protection is activated

check the elements of the output rectifiers of the power supply;
check the power supply load for a short circuit;
check the elements of the protection system (both monitoring circuits for output voltages and various protection circuits), see fig. 14:
II feedback winding TR, modulator is a tracking circuit;
T, R, modulator - current protection circuit of the output transistor T;
the "protection" line, the modulator is actually the output voltage protection;
check the feedback windings of the TR transformer (II see fig. 14);
replace the key modulator microcircuit (if any).

4. "Floating" faults, that is, faults that appear periodically.

In this case, proceed as follows:

check the elements for darkening on the case, etc .;
check the conductive tracks on the circuit board so that there are no cracks or breaks on them;
determine the places of the greatest local heating of the elements by blackening on the board and check the elements in this area.

In the event that a malfunction manifests itself during heating, the faulty element can be localized either by cooling (cotton wool moistened with acetone), or by provoking local heating of one or another element with a soldering iron. In any case, electrical safety measures should be observed.

5. Malfunctions not associated with defects in the power supply:

the protection of the power supply is triggered, in this case, an overcurrent (short circuit) of one of the output power channels is possible - determine the overloaded channel, find the cause of the short circuit of the load;
the power supply turns on for a short time, then turns off (only for power supplies with clocking from the unit by the scanning country) - in this case, you should check the feedback circuit from the line scan unit to the power supply;
the power supply does not turn on from standby from the microcontroller - check the power-on control circuit from the microcontroller to the power supply.

Printed circuit board - a necessary element in any radio engineering, from a cell phone to a TV set. It contains microcircuits, transistors, resistors, capacitors, etc. All elements are interconnected by tracks according to the schematic diagram.

Previously, the circuits of televisions and radios were assembled by surface mounting and there were no printed circuit boards. Now even a small device is more convenient to solder, then configure and repair on a printed circuit board.

After the board of the amplifier, color music, generator, power supply or other radio device has been soldered and tuned, the question arises: where is this board with all radio components, connectors, regulators, etc. place? You need a suitable case. It can be difficult or even impossible to find a ready-made one of a suitable size. Then one thing remains - to make the body with your own hands.

Now, already now we can say firmly: everyone has a TV, refrigerator, washing machine and microwave in the house. These are the most essential household appliances that are used in every home. They help us a lot in everyday life and make our life comfortable. Come on and we will be grateful to them. Or rather, we will properly exploit and take care of our assistants.

Video (click to play).

Let's take a quick look at the basic rules for the correct use of household appliances.

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