What can be cooked from squid: quick and tasty

In any electronic system powered by a switching power supply, an unpleasant moment comes when you have to deal with a problematic failure of it. Unfortunately, as practice shows, impulse radio elements or units are not as durable as we would like, therefore they require more close attention, and often just replacement or repair.

Recently, many manufacturers of switching power supplies decide repair issue or replacing your "brainchild" radically. They simply make monolithic pulse units, leaving almost no options for novice radio amateurs to repair them. But if you become the owner collapsible switching power supply, then in skillful hands and having certain knowledge and elementary skills of replacing radioelements, you can easily independently extend its service life.

General principles of operation of switching power supplies

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

For ordinary amateurs or "dummies": the general principle of operation of switching power supplies is AC voltage transformation, which is supplied directly from the 220 V socket into constant output voltages for starting and operating all other units of the system. Such a transformation is carried out with the help of appropriate pulse radioelements. The main ones are a pulse transformer and a transistor, which ensure the working functioning of all electric currents. To carry out repairs, you need to know how this unit starts up. And first, check for the presence of an input operating voltage, a fuse, a diode bridge, and so on.

Working tool for testing switching power supplies

For renovation switching power supply, you will need an ordinary, even simple multimeter that will check the DC and AC voltage. Using the functions of an ohmmeter, by ringing the resistances of radio components, you can also quickly check the health of fuses, chokes, operating resistance of resistors, "barrels" of electrolytic capacitors. As well as transistor diode junctions or diode bridges and other types of radioelements and their connections in any electronic circuit (sometimes even without soldering them completely).

Check the pulse unit first you need to in the "cold" mode. In this case, all visually suspicious (swollen or burnt radio components) are called, which can be “cold” checked without supplying operating voltage. Visually damaged radio components should be replaced immediately with new ones. If the marking has peeled off, use the schematic diagram or find the corresponding option on the Internet.

Replacement should only be done with a permissive tolerance for certain parameters, which you can find for any radioelement in specialized literature or in the circuit attached to the device. This is a safe method because switching power supplies are very insidious with their electrical discharges.

Do not forget that when detection of an inoperative radioelement, you need to check the details adjacent to it. Often, sharp voltage drops during the combustion of one element entail the failure of the neighboring ones. In the process of practical activities for the repair of certain models, you will logically calculate the malfunction based on the result of the state of the repaired object. For example, even by a certain smell (the smell of rotten eggs when the electrolyte breaks down), when turned on by a monotonous sound or crackling during the operation of the unit, and other defects that may arise during the operation of any electronic device.

In working mode pulse unit check power supply is possible only when the entire system is loaded - do not try to disconnect the TV load buses when checking. You can create a load artificially by connecting a specially assembled load equivalent.

Basic malfunctions and test methods for switching power supplies

Everyone can figure out how to turn on and set a certain mode of the multimeter, even a schoolboy. Before starting the test, make sure operability of the network cable or a switch that can be identified visually or with a multimeter. Remember to discharge the electrolytic capacitors during any check. They accumulate and hold a pretty decent charge for a certain amount of time, even after the entire system is turned off.

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

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

Self 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 period of further operation of the repaired device depend on this.

The main stages of repairing switching power supplies

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

Malfunctions of 12 volt switching power supplies

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

Hopefully this article gave general idea about the device switching power supplies. And, perhaps, even interested in many novice radio amateurs who want to improve their professional skills.

A little about the application and the UPS device

An article has already been published on the site, which tells about the UPS device. This topic can be somewhat supplemented with a short story about the repair. The abbreviation UPS is often referred to. So that there are no discrepancies, we will agree that in this article it is a Switching Power Supply.

Almost all switching power supplies used in electronic equipment are built according to two functional circuits.

Fig. 1. Functional diagrams of switching power supplies

As a rule, quite powerful power supplies, for example, computer ones, are made according to the half-bridge circuit. Power supply units for powerful stage UMZCH and welding machines are also manufactured according to the push-pull scheme.

Anyone who has ever repaired amplifiers with a power of 400 watts or more knows very well what their weight is. Naturally, we are talking about UMZCH with a traditional transformer power supply. UPSs of TVs, monitors, DVD-players are most often made according to a scheme with a single-ended output stage.

Although in reality there are other types of output stages, which are shown in Figure 2.

Fig. 2. Output stages of switching power supplies

Only the power switches and the primary winding of the power transformer are shown here.

If you look closely at Figure 1, it is easy to see that the entire circuit can be divided into two parts - primary and secondary. The primary part contains a mains filter, a mains voltage rectifier, power switches and a power transformer. This part is galvanically connected to the AC mains.

In addition to the power transformer, decoupling transformers are also used in switching power supplies, through which the control pulses of the PWM controller are fed to the gates (bases) of the power transistors. In this way, galvanic isolation from the secondary circuit is ensured. In more modern circuits, this decoupling is done using optocouplers.

The secondary circuits are galvanically isolated from the network using a power transformer: the voltage from the secondary windings is fed to the rectifier, and then to the load. The voltage stabilization and protection circuits are also powered from the secondary circuits.

Very simple switching power supplies

They are performed on the basis of an oscillator when there is no PWM master controller. An example of such a UPS is the Taschibra electronic transformer circuit.

Fig. 3. Electronic transformer Taschibra

Similar electronic transformers are produced by other companies. Their main purpose is. A distinctive feature of such a scheme is its simplicity and few details. The disadvantage is that this circuit simply does not start without load, the output voltage is unstable and has a high ripple level. But the bulbs still shine! In this case, the secondary circuit is completely decoupled from the supply network.

It is quite obvious that the repair of such a power supply unit is reduced to replacing transistors, resistors R4, R5, sometimes VDS1 and resistor R1, which acts as a fuse. There is simply nothing else in this scheme to burn out. With a low price of electronic transformers, a new one is often simply bought, and repairs are done, as they say, "out of love for art."

Safety first

Since there is such a very unpleasant neighborhood of the primary and secondary circuits, which during the repair process it is necessary, even if accidentally, to be touched with your hands, then some safety rules should be recalled.

You can touch the switched on source with only one hand, in no case with both at once. Everyone who works with electrical installations knows this. But it is better not to touch at all, or, only after disconnecting from the network by pulling the plug out of the socket. Also, do not solder something on the switched on source or just twist it with a screwdriver.

In order to ensure electrical safety on power supply boards, the "dangerous" primary side of the board is surrounded by a wide enough strip or shaded with thin stripes of paint, usually white. This is a warning that it is dangerous to touch this part of the board with your hands.

Even a switched off switching power supply can only be touched with your hands after a while, at least 2 ... 3 minutes after switching off: the charge on high-voltage capacitors remains long enough, although in any normal power supply, discharge resistors are installed in parallel to the capacitors. Remember how the school offered each other a charged capacitor! Killing, of course, will not kill, but the blow is quite sensitive.

But the worst thing is not even that: well, just think, a little pinched. If you ring the electrolytic capacitor with a multimeter immediately after turning off, then it is quite possible to go to the store for a new one.

When such a measurement is expected, the capacitor must be discharged, at least with tweezers. But it is better to do this using a resistor with a resistance of several tens of KOhms. Otherwise, the discharge is accompanied by a bunch of sparks and a rather loud click, and such a short circuit is not very useful for a capacitor.

And yet, during repairs, you have to touch the switched on switching power supply, at least to carry out some measurements. In this case, an isolation transformer, often called a safety transformer, will help to protect your loved one as much as possible from electric shock. You can read how to make it in the article.

In a nutshell, this is a transformer with two windings for 220V, with a capacity of 100 ... 200W (depending on the power of the UPS being repaired), the electrical circuit is shown in Figure 4.

Fig. 4. Safety transformer

The left winding according to the scheme is connected to the network, a faulty switching power supply is connected to the right winding through a light bulb. The most important thing with such a switch is that you can safely touch any end of the secondary winding with ONE hand, as well as all the elements of the primary circuit of the power supply.

About the role of the light bulb and its power

Most often, the repair of a switching power supply is carried out without an isolation transformer, but as an additional safety measure, the unit is turned on through a 60 ... 150W light bulb. By the behavior of the light bulb, you can, in general, judge the state of the power supply. Of course, such an inclusion will not provide a galvanic isolation from the network, it is not recommended to touch it with your hands, but it may well protect against smoke and explosions.

If, when switched on to the network, the lamp lights up at full heat, then you should look for a malfunction in the primary circuit. As a rule, this is a punctured power transistor or rectifier bridge. During normal operation of the power supply, the light first flashes brightly enough (), and then the filament continues to glow faintly.

There are several opinions about this light bulb. Someone says that it does not help to get rid of unforeseen situations, and someone believes that the risk of burning a newly sealed transistor is much reduced. We will adhere to this point of view, and use a light bulb for repairs.

About collapsible and non-collapsible cases

Most often, switching power supplies are made in housings. Suffice it to recall computer power supplies, various adapters plugged into an outlet, chargers for laptops, mobile phones, etc.

In the case of computer power supplies, everything is quite simple. Several screws are unscrewed from the metal case, the metal cover is removed and, please, the whole board with the details is already in your hands.

If the case is plastic, then you should look on the back side, where the power plug is located, for small screws. Then everything is simple and clear, he turned and removed the lid. In this case, we can say that it was just lucky.

But lately, everything has been going along the path of simplifying and reducing the cost of structures, and the halves of the plastic case are simply glued together, and quite firmly. One comrade told me how he drove a similar block to some workshop. When asked how to make it out, the masters said: "Are you not Russian?" Then they took a hammer and quickly split the body into two halves.

In fact, this is the only way to disassemble the plastic glued cases. But you need to pound carefully and not very fanatically: under the influence of blows to the body, the tracks leading to massive parts, for example, transformers or chokes, can break off.

A knife inserted into the seam also helps, and lightly tapping on it with the same hammer. However, after assembly, traces of this interference remain. But let there be minor marks on the case, but you don't have to buy a new unit.

How to find a schematic

If in the old days, circuit diagrams were attached to almost all domestic-made devices, then modern foreign electronics manufacturers do not want to share their secrets. All electronic equipment is completed only with a user manual, which shows which buttons to press. Schematic diagrams are not included with the user manual.

The device is expected to last forever or to be repaired at an authorized service center that has repair manuals called service manuals. Service centers do not have the right to share this documentation with everyone, but, praise the Internet, it is possible to find these service manuals for many devices. Sometimes this can be obtained free of charge, that is, for nothing, and sometimes the necessary information can be obtained for a small amount.

But even if the desired circuit could not be found, you should not despair, especially when repairing power supplies. Almost everything becomes clear upon closer examination of the board. This powerful transistor is nothing more than an output switch, and this microcircuit is a PWM controller.

In some controllers, the power output transistor is "hidden" inside the microcircuit. If these parts are large enough, then they have full markings, according to which you can find the technical documentation (data sheet) of the microcircuit, transistor, diode or zener diode. It is these details that form the basis of switching power supplies.

It is somewhat more difficult to find datasheets for small-sized SMD components. The full marking on the small case does not fit; instead, a code designation of several (three, four) letters and numbers is placed on the case. Using this code, with the help of tables or special programs obtained again on the Internet, it is possible, though not always, to find the reference data of an unknown element.

Measuring instruments and tools

To repair switching power supplies, you will need the tool that every radio amateur should have. First of all, these are several screwdrivers, side cutters, tweezers, sometimes pliers and even the hammer mentioned above. This is for fitting and assembly work.

For soldering work, of course, you need a soldering iron, preferably several, of various powers and dimensions. An ordinary soldering iron with a power of 25 ... 40 W is quite suitable, but it is better if it is a modern soldering iron with a thermostat and temperature stabilization.

For soldering multi-pin parts, it is good to have at hand, if not super-expensive, then at least a simple inexpensive soldering hair dryer. This will allow you to solder multi-pin parts without much effort and destruction of printed circuit boards.

To measure voltages, resistances and, more rarely, currents, you will need a digital multimeter, even if not very expensive, or a good old arrow tester. The fact that it is too early to write off the pointer device, what additional features it provides that modern digital multimeters do not have, can be read in the article.

It can provide invaluable assistance in repairing switching power supplies. Here, too, it is quite possible to use an old, not even very broadband cathode-ray oscilloscope. If, of course, there is an opportunity to purchase a modern digital oscilloscope, then this is even better. But, as practice shows, when repairing switching power supplies, you can do without an oscilloscope.

Actually, during the repair, two outcomes are possible: either repair it, or make it even worse. Here it is appropriate to recall Horner's law: "Experience grows in direct proportion to the number of equipment disabled." And although this law contains a fair amount of humor, in the practice of repair, things are exactly like this. Especially at the beginning of the journey.

troubleshooting

Switching power supplies fail much more often than other components of electronic equipment. First of all, the fact that there is a high mains voltage, which after rectification and filtering, becomes even higher. Therefore, the power switches and the entire inverter stage operate in a very heavy duty, both electrical and thermal. Most often, malfunctions lie in the primary circuit.

Faults can be divided into two types. In the first case, the failure of the switching power supply unit is accompanied by smoke, explosions, destruction and charring of parts, sometimes tracks of the printed circuit board.

It would seem that the option is the simplest, you just need to change the burnt parts, restore the tracks, and everything will work. But when trying to determine the type of microcircuit or transistor, it turns out that the marking of the part has disappeared along with the case. What happened here, without a diagram, which is often not at hand, is impossible to find out. Sometimes the repair ends at this stage.

The second type of malfunction is quiet, as Lelik said, without noise and dust. The output voltages simply disappeared without a trace. If this switching power supply is a simple power adapter, such as a charger for a cell phone or laptop, then the first thing to do is check that the output cord is working properly.

Most often, a break occurs either near the output connector or at the exit from the case. If the unit is connected to the network using a cord with a plug, then first of all, you should make sure that it is working properly.

After checking these simplest circuits, you can already climb into the jungle. As this jungle, let's take the power supply circuit of the 19-inch LG_flatron_L1919s monitor. Actually, the malfunction was quite simple: it turned on yesterday, but today it does not turn on.

Despite the seeming seriousness of the device - after all, a monitor, the power supply circuit is quite simple and intuitive.

After opening the monitor, several swollen electrolytic capacitors (C202, C206, C207) were found at the output of the power supply. In this case, it is better to change all the capacitors at once, only six of them. The cost of these parts is cheap, so you shouldn't wait for them to swell too. After such a replacement, the monitor started working. By the way, such a malfunction is quite common with LG monitors.

The swollen capacitors triggered the protection circuit, the operation of which will be discussed a little later. If, after replacing the capacitors, the power supply does not work, you will have to look for other reasons. To do this, consider the circuit in more detail.

Fig 5. Power supply unit of the LG_flatron_L1919s monitor (click on the picture to enlarge)

Line filter and rectifier

The mains voltage through the input connector SC101, fuse F101, filter LF101 goes to the rectifier bridge BD101. The rectified voltage is fed through the thermistor TH101 to the smoothing capacitor C101. This capacitor produces a constant voltage of 310V, which is supplied to the inverter.

If this voltage is absent or much less than the specified value, then check the mains fuse F101, filter LF101, rectifier bridge BD101, capacitor C101, and thermistor TH101. All these parts are easy to check with a multimeter. If there is a suspicion of a capacitor C101, then it is better to change it to a known good one.

By the way, the mains fuse doesn't just blow out. In most cases, replacing it does not restore the normal operation of the switching power supply. Therefore, you should look for other reasons leading to a blown fuse.

The fuse should be set at the same current as indicated in the diagram, and in no case should the fuse be overpowered. This can lead to even more serious malfunctions.

Inverter

The inverter is made according to a single-ended circuit. A PWM controller microcircuit U101 is used as a master oscillator, to the output of which a power transistor Q101 is connected. The primary winding of the transformer T101 is connected to the drain of this transistor through the choke FB101 (pins 3-5).

An additional winding 1-2 with a rectifier R111, D102, C103 is used to power the PWM controller U101 in the steady-state mode of the power supply. The PWM controller starts up when turned on by a resistor R108.

Output voltages

The power supply generates two voltages: 12V / 2A for powering the inverter of the backlight lamps and 5V / 2A for powering the logic part of the monitor.

From the winding 10-7 of the transformer T101 through the diode assembly D202 and the filter C204, L202, C205, a voltage of 5V / 2A is obtained.

A winding 8-6 is connected in series with the winding 10-7, from which a constant voltage of 12V / 2A is obtained using a diode assembly D201 and a filter C203, L201, C202, C206, C207.

Overload protection

Resistor R109 is connected to the source of transistor Q101. This is a current sensor, which is connected through a resistor R104 to pin 2 of the U101 microcircuit.

With an overload at the output, the current through the transistor Q101 increases, which leads to a voltage drop across the resistor R109, which is fed through the resistor R104 to the 2CS / FB pin of the U101 microcircuit and the controller stops generating control pulses (pin 6OUT). Therefore, the voltage at the output of the power supply disappears.

It was this protection that worked with swollen electrolytic capacitors, which were mentioned above.

Protection actuation level 0.9V. This level is set by the reference voltage source inside the microcircuit. In parallel with resistor R109, a zener diode ZD101 with a stabilization voltage of 3.3V is connected, which protects the 2CS / FB input from overvoltage.

To the 2CS / FB terminal through the divider R117, R118, R107, a voltage of 310V is supplied from the capacitor C101, which ensures the operation of the protection against the overvoltage of the network. The permissible range of the mains voltage at which the monitor normally operates is in the range of 90 ... 240V.

Output voltage stabilization

Made on an adjustable Zener diode U201 type A431. The output voltage 12V / 2A through the divider R204, R206 (both resistors with a tolerance of 1%) is fed to the control input R of the zener diode U201. As soon as the output voltage becomes equal to 12V, the zener diode opens and the LED of the PC201 optocoupler lights up.

As a result, the optocoupler transistor opens (pins 4, 3) and the controller supply voltage through the resistor R102 is supplied to the 2CS / FB pin. The pulses at the 6OUT pin disappear, and the voltage at the 12V / 2A output begins to drop.

The voltage at the control input R of the zener diode U201 drops below the reference voltage (2.5V), the zener diode turns off and turns off the PC201 optocoupler. Pulses appear at the 6OUT output, the voltage 12V / 2A begins to increase and the stabilization cycle repeats again. In a similar way, the stabilization circuit is built in many switching power supplies, for example, in computer ones.

Thus, it turns out that three signals are connected at once to the input of the 2CS / FB controller using a wired OR: overload protection, network overvoltage protection and the output of the output voltage stabilizer circuit.

Here it is just pertinent to recall how you can check the operation of this stabilization loop. For this, it is enough with OFF !!! from the mains power supply supply voltage from the regulated power supply to the 12V / 2A output.

It is better to hook on the output of the PC201 optocoupler with an arrow tester in the resistance measurement mode. As long as the voltage at the output of the regulated source is below 12V, the resistance at the output of the optocoupler will be large.

Now we will increase the voltage. As soon as the voltage becomes more than 12V, the arrow of the device will drop sharply in the direction of decreasing resistance. This suggests that the Zener diode U201 and the PC201 optocoupler are in good working order. Therefore, the stabilization of the output voltages should work normally.

In exactly the same way, you can check the operation of the stabilization loop in computer switching power supplies. The main thing is to figure out what voltage the zener diode is connected to.

If all these checks are successful, and the power supply does not start, then you should check the Q101 transistor by removing it from the board. With a working transistor, most likely the U101 microcircuit or its strapping is to blame. First of all, this is an electrolytic capacitor C105, which is best checked by replacing it with a known good one.

Very often my clients contact me with a problem that the power supply unit on any device does not work. Power supplies I divide it into two categories: "simple" and "complex". To "simple" I refer to antennas, power supplies from any game consoles, from portable TVs and the like, which are directly plugged into the outlet. In a word - remote, i.e. separate from the main unit. The "complex" ones in my distribution scheme are the power supplies that are in the device itself. Well, we will leave “complicated” alone for now, but let's talk about “simple” ones.

There are not very many reasons for the failure of remote controls. power supplies... I will list them all:

Open circuit in the transformer windings (primary and secondary);
Short circuit in the transformer windings;
Failure of the voltage rectifier (diode bridge, capacitor, stabilizer and associated radio elements).

If, when the unit breaks down, there are no voltages at its output at all, then, most likely, the reason is in the transformer. If there is an underestimated voltage at the output, then the matter is in the rectifiers. You can check the transformer by measuring the resistance on its windings. On the primary winding, the resistance should be more than 1 kOhm, on the secondary or secondary - less than 1 kOhm. In some power supplies, on the primary winding, under the wrapping, which the winding itself is wrapped in, a fuse is placed. To get to it, you need to break the wrapper on this winding. Most often, such a protection mechanism is present in Chinese-made transformers. So if the primary winding does not ring out, then check if a fuse may be installed on it.

With the transformer sorted out. Now let's move on to checking the voltage rectifier and its components. The most common failure in power supplies is the failure of one or more elements, of which, in fact, the voltage rectifier consists. These are the reasons we will discuss with you in this article. We will produce DIY power supply repair.

Let's consider this on the example of an antenna power supply with output voltage 12 in.

On this power supply unit, the output voltage is too low: instead of the prescribed 12 Volts, it outputs 10 Volt... So let's get down to fixing this problem. To begin with, of course, you need to disassemble the block itself. After we make sure that the transformer in this device is intact, we proceed to check the rectifier elements.

First of all, we check the diode bridge - these are four diodes to which the contacts from the secondary winding of the transformer go. I told how to check diodes in the video that you will find at the end of this article. In our block, the diode bridge is intact. Now we look at the capacitor: it happens that capacitors "swell". Our capacitor is not "swollen". If the diode bridge and capacitors are intact, we inspect the rectifier board for blackening or burning of the elements on the board.

If everything is visually in order, then feel free to solder the voltage stabilizer. This rectifier has a voltage regulator 12 Volts- 78L12. Almost always, it is this element that fails. Before removing this part from the board, remember how this part was installed on the board so that you do not reverse the polarity when replacing. Together with the stabilizer, I also recommend replacing the capacitor, this is for reliability, since most often it also fails.

After replacing these parts, check if the wires coming from the transformer have not been soldered from the contacts during the repair process.

If all is well, we collect ours. Measurements made after our repair of this power supply showed the output voltage 12 Volts, which, in general, we needed. Everything!

When diagnosing television devices, it takes immeasurably more time to find a faulty component than to replace it, especially if the search for a defect is carried out on its own, and not by a professional TV technician. Of course, it is more logical to entrust the repair to a specialist who has experience and extensive practice of this kind of work, but if there is a desire, skills in handling a soldering iron and a tester, the necessary technical documentation in the form of a circuit diagram, you can try to fix the TV at home yourself.

The power supply unit of a modern TV, whether it is a plasma panel or LCD, LED TV, is a switching power supply with a given range of output supply voltages and rated power supplied to the load for each of them. The power board can be made as a separate unit, which is typical for receivers of small diagonals, or integrated into the television chassis and located inside the device.

The characteristic signs of a malfunction of this unit are as follows:

The TV does not turn on when you press the power switch
Standby LED is on, but no transition to operating mode
Kinks and streaks in the picture, background sound
There is sound, but there is no image, which may appear after a while
Several attempts to turn on are required for normal picture and sound to appear

Let's analyze the circuitry of a standard power supply and its typical malfunctions using the ViewSonic N3260W TV as an example.

To fully view the diagram, you can open it in a new window and enlarge it, or download it to your computer or mobile device.

The first thing to start with is a thorough visual inspection of the board with the device turned off from the network. To do this, the unit must be dismantled from the TV by disconnecting the connectors, and be sure to discharge the high-voltage capacitor in the filter - C1. In the blocks of this series of TVs, the electrolytic capacitors of the filters of the secondary power supplies often fail. They are easily diagnosed by a swollen top cover. All capacitors, the appearance of which is in doubt, must be replaced immediately.

The standby unit is made on IC2 (TEA1532A) and Q4 (04N70BF) with elements of stabilization of the output voltage 5V on the optocoupler IC7 and the controlled zener diode ICS3 EA1. Absent or underestimated voltage at the output of this node, measured on capacitors CS22, CS28, indicates its malfunction. The experience of restoring this section of the circuit shows that the most vulnerable elements are IC2, Q7, ZD4 and Q11, R64, R65, R67, which need to be checked and replaced if necessary. The performance of the parts is checked by a tester directly on the block board. In this case, dubious components are soldered and tested separately, in order to exclude the influence of neighboring circuit elements on their performance. IC2 simply needs to be replaced.

If there is a 5V voltage at the output of the standby circuit, a red LED lights up on the front of the TV. At a command from the remote control or a button on the front of the TV, the power supply should go into operating mode. This command - Power_ON - in the form of a high potential of about 5V comes to pin 1 of the CNS1 connector, opening the keys on QS4 and Q11. At the same time, supply voltages are applied to the IC3 and IC1 microcircuits, transferring them to the operating mode. On the 8th pin of IC3 directly from the collector of Q11, on the 12th pin of IC1 through the switch Q9 after starting the PFC circuit. The performance of the Power Factor Correction circuit is indirectly determined by the increase in voltage from 310 volts to 390 volts measured across capacitor C1. If there are output supply voltages 12V and 24V, then the main source on IC3, Q1, Q2 functions in normal mode. Practice shows the low reliability of the UCC28051 and LD6598D in critical conditions, when the filtration of secondary sources deteriorates, and their replacement is routine.

Summarizing the experience of repairing TV power supplies, it should be noted that the weakest link in their composition are filter capacitors, which lose their properties and nominal parameters over time. Sometimes the faulty "container" is visible by the swollen lid, sometimes not. The consequences of poor filtering of the rectified voltage can be very different: from the loss of the power supply itself, to damage to the elements of the inverter or a software failure on the memory chips on the motherboard.

It is very difficult to independently figure out all the causes and consequences when repairing a power supply unit of a modern TV, to diagnose it correctly without special tools and devices. Our advice in such cases is. This will not hit the pocket hard at the current low prices for the repair of television equipment and will save time.

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Bravis LED-16E96B TV after voltage drop.

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

SW2658 is a typical diagram. Chinese TV PSU adapter.

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 can be opened using a non-sharp screwdriver and a hammer. Light blows to the seam. Then, with a wide screwdriver, it peels further.

Visually, one of the network capacitors 15 microfarads x 400 volts swelled.
The fuse is naturally broken. It crashed well, the board had to be washed in some places with alcohol.

At first, I did not even realize why the board got smoked. Later, a torn choke L1 wound on a ferrite core called under the silicone. I rewound it with the same wire.

I had to throw out only 15 centimeters of the wire. It was coiled round to round. I wound it not so neatly, the first layers evenly, then how it happened. This did not affect the performance in any way.

Choke in PSU with burnt wire

I had to remember the old technology)
Took a beloved PWM controller, which used to be installed in DVD, receivers, adapters ... 5H0165R.

Transformer ( 1

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

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

The cause of a break or burnout is a thin wire that cannot withstand mains voltage surges and overloads. Let's say thanks to the Chinese, they are thrifty guys, they don't want to wind a thicker wire ...

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

25.5 ohm , which is also normal.

C1 (100uF 16V) 470 uF (25V)

It is not necessary to know the pinout (location and purpose) of the 78L12 stabilizer terminals; you must either remember, sketch or photograph the location of the faulty microcircuit on the electronic board and solder the defective part as soon as you find it. This simple operation will save your time if a faulty microcircuit is dropped out, 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, radio telephones, and chargers. Despite the active introduction of switching power supplies, transformer power supplies are still actively used and find application in the user's everyday life.

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

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

So, let's take a look at the composition of an ordinary low-power power supply and its repair

An adapter for 12V and a current of 100mA with a power of 3.6 watts from an antenna amplifier got on the repair table.

The photo shows the adapter after the repair.

What parts does a conventional transformer adapter consist of?

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

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

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

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

It is quite simple to check the health of the transformer. It is necessary to measure the resistance of the primary and secondary windings. The resistance of the primary winding should be several kilo-ohms (1kΩ = 1000 ohms), the secondary one - several tens of ohms.

When checking the transformer of the adapter for the primary winding, the resistance turned out to be 1.8 kOhm, which indicates the serviceability of the primary winding.

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

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

We disassemble the power supply, make an external examination. Pay attention to the darkened areas around the radio components, chips and cracks on the cases of the power stabilizer (78L12), swollen filter capacitors.

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

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.

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 the other elements associated with it (power filter, power cable, input) 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 examine the board, since it often fails at the same time as other elements.

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

In this case, he does not need to ring out, but simply gets drunk. The following elements are also soldered and called:

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 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.

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.

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.

Breakdown reasons:

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!).

What if there is no output voltage?

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 suitable wire 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 visually detected).

Before, it is imperative to study the rules for the safe use of such a tool. Such a device must not shine into reflective surfaces, as it can damage the eyes.

It is quite possible to build it yourself. A fan is used as a blower, and a spiral is used as a heater. The most optimal option is a thyristor circuit.

Breakdown reasons:

poor ventilation.

Solution:

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.

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

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