Repair of a 12 volt switching power supply. How to repair a switching power supply yourself? There are several reasons here, but the main ones are

Bravis LED-16E96B TV after a voltage drop.

The power supply is assembled on a PWM controller SW2658a.
The microcircuit is rare, but strangely enough there is a datasheet available. And nothing more.

SW2658-type-diagram. PSU adapter for Chinese TV.

The power adapter, as expected, died with special effects.
The TV itself was not damaged, I checked it using a working power supply.

The adapter is opened using a non-sharp screwdriver and a hammer. Light blows on the seam. Then, using a wide screwdriver, it is peeled further.

Visually, one of the network capacitors 15 uF x 400 volts was swollen.
Naturally the fuse is broken. It made a good noise, and in some places the board had to be washed with alcohol.

At first I didn’t even realize why the board was so smoked. Later, under the silicone, a torn inductor L1 wound on a ferrite core rang. I wired it with the same wire.

I had to throw out only 15 centimeters of wire. It was wound turn to turn. I didn’t wind it so neatly, the first layers were even, and then how it turned out. This did not affect performance in any way.

Choke in power supply with burnt wire

I had to remember the old technology)
I took my favorite PWM controller, which used to be installed in DVDs, receivers, adapters... 5H0165R.

Transformer ( 1

The electronic circuit serves to rectify the alternating voltage (converting it into direct voltage) and stabilize the output voltage at 12 V.

On the circuit diagram T1 – transformer. Typical transformer malfunctions are burnout or breakage of the wire of the primary winding, less often the secondary winding. As a rule, the primary, network winding is faulty ( 1 ).

The cause of a break or burnout is a thin wire that cannot withstand network surges and overloads. Let's say thank you to the Chinese, they are frugal guys, they don't want to run thicker wires...

The resistance of the primary winding should be several kilo-ohms (1 kOhm = 1000 Ohms), the secondary winding should be several tens of Ohms.

25.5 Ohm , which is also normal.

C1 (100uF 16V) 470 µF (25V)

It is not necessary to know the pinout (location and purpose) of the terminals of the 78L12 stabilizer; you must either remember, sketch or photograph the location of the faulty microcircuit on the electronic board and solder the working part as soon as you find it. This simple operation will save your time if you soldered a faulty microcircuit, but a replacement was not found in time and you forgot how the microcircuit was soldered.

Network power adapters - miniature power supplies for various electronic household equipment are used to power antenna amplifiers, radiotelephones, chargers. Despite the active introduction of switching power supplies, transformer blocks supplies are still actively used and are used in the user’s everyday life.

It is not uncommon for these transformer units to fail or break.

If the adapter breaks, you can replace it with a new one, the cost is low. But why give your hard-earned money if in most cases you can fix the problem yourself within 15 to 30 minutes and save yourself from searching for a replacement and wasting money?

So, let’s look at the composition of a conventional low-power power supply and its repair.

An adapter for 12V and a current of 100mA with a power of 3.6 Watts from the antenna amplifier came to the repair table.

The photo shows the adapter after the repair.

What parts does a typical transformer adapter consist of?

If we disassemble the adapter, we will find a transformer inside ( 1 ) and a small electronic circuit ( 2 ).

Transformer ( 1 ) serves to reduce the 220V alternating mains voltage to the level of 13 - 15 V.

The electronic circuit serves to rectify the alternating voltage (converting it into direct voltage) and stabilize the output voltage at 12 V.
It's simple. What can break in such a simple device?

Let's take a look at the circuit diagram of this adapter.

On the circuit diagram T1 – transformer. Typical faults transformer are burnout or breakage of the wire of the primary, less often the secondary winding. As a rule, the primary, network winding is faulty ( 1 ).

The cause of a break or burnout is a thin wire that cannot withstand network surges and overloads. Let's say thank you to the Chinese, they are frugal guys, they don't want to run thicker wires...

Checking the health of the transformer is quite simple. It is necessary to measure the resistance of the primary and secondary windings. Resistance primary winding should be several units of kilo-ohms (1 kOhm = 1000 Ohms), the secondary - several tens of Ohms.

When checking the adapter transformer for the primary winding, the resistance turned out to be 1.8 kOhm, which indicates that the primary winding is working properly.

For the secondary winding the resistance was 25.5 Ohm , which is also normal.

If there is no indication, you should measure the resistance of the primary winding of the transformer. This is easy to do; you don’t even have to disassemble the power supply, but measure the winding resistance through the contacts of the power plug.

We disassemble the power supply and perform an external inspection. Please pay attention to the darkened areas around the radio components, chips and cracks on the housings of the power stabilizer (78L12), and swelling of the filter capacitors.

During the repair of the antenna adapter, it turned out that the 78L12 stabilizer chip was faulty. The electrolytic capacitor was also replaced C1 (100uF 16V) to a capacitor with a larger capacity - 470 µF (25V) . When replacing a capacitor, the polarity of the capacitor must be taken into account.

It is not necessary to know the pinout (location and purpose) of the terminals of the 78L12 stabilizer; you must either remember, sketch or photograph the location of the faulty microcircuit on the electronic board and solder the working part as soon as you find it. This simple operation will save your time if you unsoldered a faulty microcircuit, but a replacement was not found in time and you forgot how the microcircuit was soldered.

A switching power supply is built into most household appliances. As practice shows, this particular unit quite often fails, requiring replacement.

The high voltage constantly passing through the power supply does not have the best effect on its elements. And the point here is not the mistakes of the manufacturers. By increasing the service life by installing additional protection, you can achieve the reliability of the protected parts, but lose it on newly installed ones. In addition, additional elements complicate repairs - it becomes difficult to understand all the intricacies of the resulting circuit.

Manufacturers solved this problem radically by reducing the cost of the UPS and making it monolithic and non-separable. Such disposable devices are becoming more common. But, if you are lucky - the collapsible unit has failed, independent repair is quite possible.

The operating principle of all UPSs is the same. The differences relate only to the diagrams and types of parts. Therefore, it is quite simple to understand the breakdown, having basic knowledge of electrical engineering.

For repairs you will need a voltmeter.

It is used to measure 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 elements associated with it (surge filter, power cable, input) are in good order.

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

If there is no voltage, you need to ring the diodes of the rectifier bridge, the capacitor, the fuse itself, and so on. The tricky thing about fuses is that, once they fail, they look no different from working samples. A fault can only be detected through a continuity test - a blown fuse will show high resistance.

Having discovered a faulty fuse, you should carefully inspect the board, since it often fails simultaneously with other elements.

A damaged capacitor is easy to spot naked eye– it will be destroyed or swollen.

In this case, he does not need to be called, but simply disappears. The following elements are also soldered and ringed:

• power or rectifier bridge (looks like a monolithic block or can 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 power switches).

Important. All parts are desoldered and replaced at the same time! Replacing one at a time will lead to burnout of the power unit each time.

Burnt out elements must be replaced with new ones. The radio market offers a wide range of parts for power supplies. It’s quite easy to find good options at minimal prices.

On a note. The fuse can be successfully replaced with a piece of copper wire. A wire thickness of 0.11 millimeters corresponds to a 3 Ampere fuse.

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

Solution this malfunction of switching power supplies:

• install protection (it is not always possible to select the right part);
• or use a mains voltage filter with good protective elements (not jumpers!).

What to do if there is no output voltage?

Another common cause of power supply failure has nothing to do with the fuse. We are talking about the absence of output voltage when such an element is fully operational.
Solution:

1. Swollen capacitor - requires desoldering and replacement.
2. A failed inductor - it is necessary to remove the element and change the winding. The damaged wire is unwound. At the same time, the turns are counted. Then a new suitable wire is wound at the same number of turns. The part is returned to its place.
3. Deformed bridge diodes are replaced with new ones.
4. If necessary, parts are checked by a tester (if no damage is visually detected).

Before that, it is necessary to study the rules for the safe use of such a tool. You should not shine such a device into reflective surfaces, as this can damage your eyes.

It is quite possible to build it yourself. A fan is used as a blower, and a coil is used as a heater. The best option is a circuit with a thyristor.

Causes of failure:

• poor ventilation.

Solution:

• do not cover ventilation openings;
• ensure optimal temperature conditions - cooling and ventilation.

What you need to remember:

1. The first connection of the unit is made to a 25 Watt lamp. This is especially important after replacing diodes or transistors! If an error is made somewhere or a malfunction is not noticed, the passing current will not damage the entire device as a whole.
2. 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 can't do this directly. It is necessary to short-circuit through a resistance rated higher than 0.5 V.

If the entire UPS has been thoroughly checked, but still does not work, you can contact a repair shop. Perhaps your case relates to a complex breakdown that is still fixable.

According to statistics, about 5% of breakdowns require unit replacement. Fortunately, this device is always available. In stores you can find a rich assortment in different price categories.

At any electronic system, operating from a switching power supply, an unpleasant moment comes when you have to deal with its problematic failure. Unfortunately, pulsed radio elements or units, as practice shows, are not as durable as we would like, and therefore require more careful attention, and often simply replacement or repair.

IN Lately many manufacturers of switching power supplies decide repair issue or replacing your “brainchild” radically. They simply make monolithic pulse units, leaving virtually no options for novice radio amateurs to repair them. But if you become the owner collapsible switching power supply, then in in capable hands and having certain knowledge and basic skills in replacing radio elements, you can easily extend its service life on your own.

General principles of operation of switching power supplies

Let's first deal with general operating principle any switching power supply. Moreover, the main operating functions and even output voltages for certain models, which are necessary for the functioning of the entire system (be it a TV or another version of an electronic device), are almost the same for all pulse generators. Only the individual schematic drawings and the radioelements used and their parameters differ. But this is no longer so important for understanding the general principle of its operation.

For simple fans or “dummies”: general principle operation of switching power supplies is AC voltage transformation, which is supplied directly from a 220 V socket to a constant output voltage to start and operate all other units of the system. This transformation is carried out using appropriate pulsed radioelements. The main ones are a pulse transformer and a transistor, which ensure the operational functioning of all electrical flows. To carry out repairs, you need to know how this unit starts. First, check the presence of input operating voltage, fuse, diode bridge, and so on.

Working tool for testing switching power supplies

For repair switching power supply, you will need a regular, even simple multimeter that will check the constant and AC voltage. Using the functions of an ohmmeter, by ringing the resistance of radio components, you can also quickly check the serviceability of fuses, chokes, the operating resistance of resistors, and the “barrels” of electrolytic capacitors. As well as transistor diode junctions or diode bridges and other types of radio elements and their connections in any electronic circuit(sometimes without even desoldering them completely).

Check pulse block First you need to do it in “cold” mode. In this case, all visually suspicious (swollen or burnt radio components) are called up, which can be checked “cold” without applying operating voltage. Visually damaged radio components should be immediately replaced with new ones. If the markings have peeled off, use circuit diagram or find the appropriate option on the Internet.

Replacement must be made only with a permit according to certain parameters, which you can find for any radio element in specialized literature or in the diagram supplied with the device. This is a safe method, because switching power supplies are very insidious with their electrical discharges.

Don't forget that when detection of a non-working radio element, you need to check the parts adjacent to it. Often, sudden voltage drops during the combustion of one element lead to the failure of neighboring ones. In the process of practical work on repairing certain models, you will logically calculate the fault based on the result of the condition of the object being repaired. For example, even by a certain smell (the smell of rotten eggs when the electrolyte fails), when turned on, by a monotonous sound or crackling sound during the operation of the unit and other defects that may arise during the operation of any electronic device.

In working mode pulse block check power supply is possible only when the entire system is loaded - do not even think about disconnecting the TV’s load buses when checking. You can create a load artificially by connecting a specially assembled load equivalent.

Basic faults and methods for checking switching power supplies

Everyone can figure out how to turn on and set a certain multimeter mode on their own, even a schoolchild. Before starting the test, make sure network cable performance or switch, which can be determined visually or using a multimeter. Be sure to discharge the electrolytic capacitors during any inspection. They accumulate and hold a fairly decent charge for a certain time, even after the entire system is turned off.

Possible reasons failure of the switching power supply and necessary replacement non-working radio elements:

1. When the fuse blows, the entire unit is de-energized. Replacing a burnt out contact is very easy. Use regular wire hair that is wound over the fuse or soldered directly to its contacts. It is necessary to take into account the thickness of the hair, which is designed for a certain current strength. Otherwise, you risk subsequently destroying the entire pulse unit if the fuse does not work.
2. If completely absent output voltage, the corresponding capacitor or inductor may be faulty and need to be replaced or the winding changed. To do this, you need to unwind the damaged wire and wind a new one with the appropriate number of turns and a suitable cross-section. After which the homemade choke is soldered into its workplace.
3. Check all diode bridges and transitions. How to do this is described above. When installing new parts, do not forget to do your own, and most importantly, high-quality soldering.

Independent and high-quality soldering

Correct and high-quality soldering is one of the fundamental skills that any aspiring radio amateur should master. The final result of the entire repair and the continued operation of the repaired device depend on this.

Main stages of repair of switching power supplies

Possible faults typical switching power supplies using the example of a TV or computer:

Malfunctions of 12 volt switching power supplies

The difficulty in replacing any 12 V switching power supply is finding the right model, and they are very diverse. Therefore find such a block with the required output voltage and current is not always possible if it is needed quickly. Sometimes it is easier, in case of minor damage, to restore its functionality yourself. Here are some tips for this:

We hope this article has given general idea about the design of switching power supplies. And, perhaps, even interested many novice radio amateurs who want to improve their professional skills.

Nowadays, almost all household electrical appliances have special devices called pulse units. They can take the form of either a separate module or a board located in the device design.

Impulse power block

Since pulse units are designed to rectify and reduce the mains voltage, they can often fail. Therefore, in order not to buy a new expensive household device, knowledge of how to fix it with your own hands will be quite in demand. How to identify malfunctions of this device or board, as well as how to repair it yourself, this article will tell you.

Description of the voltage converter

The switching power supply can be in the form of a board or an independent remote module. It is intended, as already mentioned, to reduce and rectify the mains voltage. Its necessity is based on the fact that the standard power supply has a voltage of 220 volts, and for the operation of many household appliances a much lower value of this parameter is required.
Today, instead of standard buck-rectifier circuits based on diode bridge and power transformer, pulsed voltage conversion power supplies are used.

Note! Despite the presence of high circuit reliability, switching power supplies often break down. Therefore, nowadays it is very important to repair these elements of electrical circuits.

Switching power supply circuit

All types of pulsed power supply (built-in or external to the device) have two functional blocks:

• high voltage. In such a power supply, the mains voltage is converted to DC using a diode bridge. Moreover, the voltage is smoothed to a level of 300.0...310.0 volts on the capacitor. The result is a transformation high voltage pulsed with a frequency of 10.0...100.0 kilohertz;

Note! This design of the high-voltage unit made it possible to abandon massive low-frequency step-down transformers.

• low voltage. Here the pulse voltage is reduced to an unnecessary level. In this case, the tension is smoothed out and stabilized.

As a result of this structure, at the output of the switching type power supply, several or one voltage is observed, which is needed to power household appliances.
It is worth noting that the low-voltage unit can contain a variety of control circuits that increase the reliability of the device.

Switching power supply (board). Colors are shown in the diagram

Since power supplies of this type have a complex structure, their proper DIY repair must rely on some knowledge in electronics.
When repairing this device, do not forget that some of its elements may be under mains voltage. In this regard, even when conducting an initial inspection of the unit, extreme caution must be observed.
Repair in most cases will not cause complications, because... Switching power supplies have a standard design. Therefore, their faults will also be similar, and do-it-yourself repairs look like a completely feasible task.

Possible causes of failure

Malfunctions that render a switching power supply inoperative can occur for a variety of reasons. Most often breakdowns occur due to:

• presence of mains voltage fluctuations. A malfunction can be caused by vibrations for which these buck-rectifier modules are not designed;
• connecting to the power supply loads that household appliances are not designed for;
• lack of protection. By not installing protection, some manufacturers simply save money. If such a problem is detected, you just need to install the protection in a specific place where it should be;
• failure to comply with operating rules and recommendations specified by manufacturers for specific models.

At the same time, recently common cause Breakdown of voltage converters is due to manufacturing defects or the use of low-quality parts during assembly. Therefore, if you want your purchased switching power supply to work as long as possible, you should not buy it in dubious places and not from trusted people. Otherwise, it might just be wasted money.
After diagnosing the unit, the following faults are often discovered:

• 40% of cases – malfunction of the high-voltage part. This is evidenced by the burnout of the diode bridge, as well as the breakdown of the filter capacitor;
• 30% - breakdown of a bipolar (forming high-frequency pulses and located in the high-voltage part of the device) or power field-effect transistor;
• 15% - breakdown of the diode bridge in its low-voltage part;

Diode bridge

• Burnout (breakdown) of the inductor windings on the output filter is rare.

All other breakdowns can only be determined using special equipment, which is unlikely to be kept at home by the average person. For a deeper and more accurate check it is necessary digital voltmeter and an oscilloscope. Therefore, if the breakdown does not lie in the four options above, then you will not be able to repair a power supply of this type at home.
As you can see, repairs carried out in this situation with your own hands can take a wide variety of forms. Therefore, if your computer or TV has stopped working due to a broken power supply, then you do not need to run to a repair service, but you can try to solve the problem on your own. At the same time, home repairs will cost significantly less. But if you cannot cope with the task on your own, then you can already go to the specialists from the repair service.

Failure detection algorithm

Any repair always begins with finding out the cause of the malfunction of the switching power supply.

Note! To repair and troubleshoot a switching power supply, you will need a voltmeter.

Voltmeter

In order to identify it, you must adhere to the following algorithm:

• disassemble the power supply;
• using a voltmeter we measure the voltage that is present on the electrolytic capacitor;

Measuring the voltage on an electrolytic capacitor

• if the voltmeter produces a voltage of 300 V, then this means that the fuse and all elements of the electrical network (power cable, line filter, input chokes) associated with it are working normally;
• in models with two small capacitors, the voltage indicating their serviceability, which is given by the voltmeter, should be 150 V for each device;
• if there is no voltage, then it is necessary to test the diodes of the rectifier bridge, fuse and capacitor;

Note! The most insidious elements in the electrical circuit of a switching type power supply are fuses. There is no evidence of their failure external signs. Only dialing will help you identify their malfunction. If burned, they will produce high resistance.

Switching Power Supply Fuses

• if a faulty fuse is detected, then you need to check the remaining elements of the electrical circuit, since they rarely burn out alone;
• From the outside it is quite easy to identify a damaged capacitor. It usually swells or collapses. Repair in this case will consist of desoldering it and replacing it with a functional one.
• It is imperative to check the following elements for serviceability:
• rectifier or power bridge. It has the form of a monolithic block or is organized from four diodes;

Switching power supply power bridge

• filter capacitor. It may look like one or more blocks that are connected to each other in series or in parallel. Typically the filter capacitor is located in the high-voltage part of the block;
• transistors placed on the radiator.

Pay attention! When carrying out repairs, you need to immediately find all the faulty parts of the switching power supply, since they should be desoldered and replaced at the same time! Otherwise, replacing one element will lead to burnout of the power unit.

Features of repair work and tools for them

For a standard type of device, the above stages of diagnostics and repair work will be identical. This is due to the fact that they all have a typical structure.

Soldering parts to the board

Also, in order to conduct quality do-it-yourself repair pulse voltage converter, you need a good soldering iron, as well as the ability to operate it. In this case, you will also need solder, alcohol, which can be replaced with purified gasoline, and flux.
In addition to a soldering iron, the following tools will definitely be needed for repairs:

• Screwdriver Set;
• tweezers;
• household multimeter or voltmeter;
• incandescent lamp. Can be used as ballast load.

With such a set of tools, anyone can do simple repairs.

Carrying out repair work

When planning to repair a damaged pulse voltage converter with your own hands, you need to understand that such manipulations are not carried out for products intended for complex replacement. They are not designed for repair and no technician will undertake to repair them, since it requires complete dismantling of the electronic filling and replacing it with a new working one.

Power supply board impulse principle work

In all other cases, repairs at home and with your own hands are quite possible.
Proper diagnosis is half the repair. Faults associated with the high-voltage part can be easily detected both visually and using a voltmeter. But a fuse malfunction can be detected if there is no voltage in the area after it.
If faults are detected with its help, all that remains is to simply replace them simultaneously. When carrying out repair work, it is necessary to rely on the appearance of the electronic board. Sometimes, in order to check each part, it is necessary to unsolder it and test it with a multimeter. It is advisable to check all details. Despite the difficulty of such a process, it will allow us to identify all damaged elements of the electrical circuit and replace them in time to prevent burnouts of the device in the foreseeable future.

Replacing burnt out parts

After all the burnt out parts have been replaced, you need to install a new fuse and check the repaired power supply by turning it on. Usually, if everything was done correctly, and all standards and instructions for repair work were followed, the converter will work.

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 besides photographs appearance, parameters and prices for them, I didn’t find anything. 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 blown 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.

If you have repaired a UPS, then you have probably encountered this situation: all faulty elements have been replaced, the remaining ones seem to have been checked, but you turn on the TV and... bam... and everything has to start all over again! There are no miracles in radio engineering, and if something doesn’t work, there’s a reason for it! Our task is to find her!

The UPS is the most unreliable component in modern radio devices. This is understandable - huge currents, high voltages - after all, all the power consumed by the device passes through the UPS. At the same time, let’s not forget that the amount of power supplied by the UPS to the load can change tens of times, which cannot have a beneficial effect on its operation.

Most manufacturers use simple circuits UPS. This is understandable. The presence of several levels of protection can often only complicate repairs and have virtually no effect on reliability, since the increase in reliability due to an additional protection loop is compensated by unreliability additional elements, and during repairs we have to spend a long time figuring out what these parts are and why they are needed. Of course, each UPS has its own characteristics, differing in the power supplied to the load, the stability of the output voltages, the operating range mains voltage and other characteristics that play a role during repairs only when you need to choose a replacement for a missing part.

It is clear that when making repairs it is advisable to have a diagram. Well, if it’s not there, simple TVs can be repaired without it. The operating principle of all UPSs is almost the same, the only difference is in the circuit designs and types of parts used.

I use a technique developed over many years of repair experience. More precisely, this is not a technique, but a set of mandatory actions for repairs, proven by practice.

The proposed method assumes that you are at least somewhat familiar with how a TV works. For repairs, you need a tester (avometer) and, preferably, but not necessarily, an oscilloscope.

So, let's repair the power supply.

They brought you a TV or yours got damaged.

Turn on the TV, make sure that it is not working, that the standby indicator is not on. If it is on, then the problem is most likely not in the UPS. Just in case, you will need to check the horizontal scan supply voltage.

Turn off the TV and take it apart.

External inspection of the TV board, especially the area where the UPS is located. Sometimes swollen capacitors, burnt resistors, etc. can be found.

We'll have to check them out in the future.

Carefully examine the soldering, especially the transformer, key transistor/chip, and chokes.

Check the power circuit: check the power cord, fuse, power switch - if there is one, chokes in the power circuit, rectifier bridge.

Often, with a faulty UPS, the fuse does not blow - it simply does not have time. If the key transistor breaks through, the ballast resistance is more likely to burn out than the fuse. It happens that the fuse burns due to a malfunction of the posistor, which controls the demagnetizing device (demagnetization loop). Be sure to check on short circuit the terminals of the mains power filter capacitor without desoldering it, since in this way you can often check for breakdown the collector-emitter terminals of a key transistor or microcircuit if a power switch is built into it. Sometimes power is supplied to the circuit from the filter capacitor through ballast resistors, and if they break, it is necessary to check for breakdown directly at the switch electrodes.

Take a moment to check the remaining parts of the unit - diodes, transistors, some resistors. First, we check without desoldering the part; desoldering it only when there is a suspicion that the part may be faulty. In most cases, such a check is sufficient. Ballast resistors often break. Ballast resistances have a small value (tenths of an Ohm, units of Ohm) and are designed to limit pulse currents, as well as for protection as fuses.

We need to see if there are any short circuits in the secondary power circuits - to do this, we check the terminals of the capacitors of the corresponding filters at the outputs of the rectifiers for short circuits.

After completing all checks and replacing faulty parts, you can perform a live test. To do this, instead of the mains fuse, we connect a 150-200 Watt 220 Volt light bulb. This is necessary so that the light bulb protects the UPS in case the malfunction is not resolved. Disconnect the degaussing device.

Turn it on. There are three options:

1. The light flashed brightly, then went out, and a raster appeared. Or the standby mode indicator lights up. In both cases, you need to measure the voltage supplying the horizontal scan - it varies for different TVs, but not more than 125 Volts. Often its value is written on the printed circuit board, sometimes near the rectifier, sometimes near the TDKS. If it is increased to 150-160 Volts, and the TV is in standby mode, then switch it to operating mode; some TVs allow voltages to be increased by Idling(when horizontal scanning does not work). If the voltage is too high in operating mode, check the electrolytic capacitors in the power supply only by replacing them with a known good one. The fact is that often the electrolytic capacitors in the UPS lose frequency properties and at the generation frequency they cease to perform their functions, despite the fact that when checked by a tester using the charge-discharge method, the capacitor seems to be in good order. The optocoupler (if there is one) or the optocoupler control circuit may also be faulty. Check whether the output voltage is regulated by internal regulation (if any). If it is not adjustable, then you need to continue searching for faulty parts.
2. The light flashed brightly and went out. Neither the raster nor the standby mode indication appeared. This indicates that the UPS does not start. It is necessary to measure the voltage on the surge protector capacitor, it should be 280-300 Volts. If it is not there, sometimes they put a ballast resistor between the mains rectifier bridge and the capacitor. Check the power supply and rectifier circuits again. If the voltage is too low, one of the diodes of the mains rectifier bridge may be broken or, what is more common, the mains power filter capacitor may have lost capacity. If the voltage is normal, then you need to once again check the rectifiers of the secondary power supplies, as well as the starting circuit. The triggering circuit for simple TVs consists of several resistors connected in series. When testing a circuit, you need to measure the voltage drop across each of them, measuring the voltage directly at the terminals of each resistor.
3. The light is on at full brightness. Turn off the TV immediately. Recheck all items. And remember - there are no miracles in radio engineering, it means you missed something somewhere, you didn’t check everything.

95% of the faults fit into this diagram, but there are more complex faults when you have to rack your brains. For such cases, you cannot write methods and you cannot create instructions.