The computer's power supply is not working. How to repair a computer power supply with your own hands. Searching for faulty electrolytic capacitors in the power supply

One of the important components of a modern personal computer is the power supply unit (PSU). If there is no power, the computer will not work.

On the other hand, if the power supply produces voltage beyond the permissible limits, this can cause failure of important and expensive components.

ATX computer power supply circuit

In such a unit, with the help of an inverter, the rectified mains voltage is converted into high-frequency alternating voltage, from which the low voltage flows necessary for computer operation are formed.

The ATX power supply circuit consists of 2 nodes - a mains voltage rectifier and a voltage converter for the computer. The mains rectifier is a bridge circuit with a capacitive filter. A constant voltage of 260 to 340 V is generated at the output of the device.

The main elements of the voltage converter are:

• an inverter that converts direct voltage into alternating voltage;
• high-frequency transformer operating at a frequency of 60 kHz;
• low-voltage rectifiers with filters;
• control device.

In addition, the converter includes a standby voltage power supply, amplifiers for the control signal of key transistors, protection and stabilization circuits, as well as other elements.

The inverter includes two power transistors operating in switching mode and controlled using signals with a frequency of 60 kHz coming from a control circuit implemented on the TL494 chip.

A pulse transformer is used as the inverter load, from which the voltages +3.3 V, +5 V, +12 V, -5 V, -12 V are removed, rectified and filtered.

Main causes of malfunctions

The causes of malfunctions in the power supply can be:

• surges and fluctuations in supply voltage;
• poor quality manufacturing of the product;
• overheating due to poor fan performance.

Malfunctions usually lead to the fact that the computer system unit stops starting or turns off after a short period of operation. In other cases, despite the operation of other units, the motherboard does not start.

Before starting repairs, you need to finally make sure that it is the power supply that is faulty. In this case, you first need to check the functionality of the network cable and the power switch. After making sure that they are in good condition, you can disconnect the cables and remove the power supply from the system unit case.

Before you turn on the power supply autonomously again, you need to connect the load to it. To do this, you will need resistors that are connected to the corresponding terminals.

In this case, the value of the resistance of the load resistors must be selected so that currents flow through the circuits, the values ​​​​of which correspond to the nominal values.

The power dissipation of the resistors must correspond to the rated voltages and currents.

First you need to check the influence of the motherboard. To do this, you need to close two contacts on the power supply connector. On a 20-pin connector, these will be pin 14 (the wire that carries the Power On signal) and pin 15 (the wire that corresponds to the GND - Ground pin). For a 24-pin connector, these will be pins 16 and 17, respectively.

The serviceability of the power supply can be assessed by the rotation of its fan. If the fan rotates, the power supply is working.

Next, you need to check that the voltages at the unit connector correspond to their nominal values. It should be taken into account that, in accordance with the documentation for the ATX power supply, the deviation of voltage values ​​for the -12V power circuit is allowed within ± 10%, and for other power circuits ± 5%. If these conditions are not met, you must proceed to repair the power supply.

ATX computer power supply repair

After removing the cover from the power supply, you must immediately clean all dust from it using a vacuum cleaner. It is because of dust that radio components often fail, since dust, covering the part with a thick layer, causes overheating of such parts.

The next step in troubleshooting is a thorough inspection of all elements. Particular attention should be paid to electrolytic capacitors. The reason for their breakdown may be severe temperature conditions. Faulty capacitors usually swell and leak electrolyte.

Such parts must be replaced with new ones with the same ratings and operating voltages. Sometimes the appearance of the capacitor does not indicate its malfunction. If, based on indirect signs, there is a suspicion of poor performance, then you can check the capacitor with a multimeter. But for this it needs to be removed from the circuit.

Deterioration in thermal conditions inside the unit may be due to poor performance of the cooler. To improve performance, it must be cleaned of dust and the bearings lubricated with machine oil.

A faulty power supply can also be caused by faulty low-voltage diodes. To check, you need to measure the resistance of the forward and reverse transitions of the elements using a multimeter. To replace faulty diodes, you must use the same Schottky diodes.

The next malfunction that can be determined visually is the formation of ring cracks that break the contacts. To detect such defects, you need to carefully examine the printed circuit board. To eliminate such defects, it is necessary to carefully solder the places where cracks form (for this you need to know how to solder correctly with a soldering iron).

Resistors, fuses, inductors, and transformers are inspected in the same way.

If a fuse is blown, it can be replaced with another one or repaired. The power supply uses a special element that has leads for soldering. To repair a faulty fuse, it is removed from the circuit. Then the metal cups are heated and removed from the glass tube. Then select a wire of the desired diameter.

The wire diameter required for a given current can be found in the tables. For the 5A ATX fuse used in the circuit of the ATX power supply, the diameter of the copper wire will be 0.175 mm. Then the wire is inserted into the holes of the fuse cups and fixed by soldering. The repaired fuse can be soldered into the circuit.

The most common malfunctions of a computer power supply are discussed above.

Detecting and repairing more complex faults requires good technical training and more sophisticated measuring instruments, such as an oscilloscope.

In addition, elements that need to be replaced are often in short supply and are quite expensive. Therefore, in case of a complex malfunction, you should always compare the costs of repairs and the costs of purchasing a new power supply. It often happens that it is more profitable to purchase a new one.

1. One of the most important elements of a PC is the power supply; if it fails, the computer stops working.
2. The computer power supply is a rather complex device, but in some cases you can repair it yourself.

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elektrik24.net

How to repair your computer power supply yourself?

Repairing a computer power supply yourself is quite a difficult task. Having undertaken this, you should clearly understand which of the components requires repair. Also, you should understand that if the device is under warranty, then after any intervention the warranty card immediately expires.

If the user has little skills in working with electrical appliances and is confident that he will not make mistakes, then he can safely take on such work. You should remember to be careful when working with electrical appliances.

Computer power supply circuit

To create galvanic isolation, a transformer with a large number of windings is required. Based on this, a computer requires quite a lot of power and it is natural that such a transformer for a PC should be large and of considerable weight.

But due to the frequency of the current required to create the magnetic field, much fewer turns are required on the transformer. Thanks to this, when using a converter, small and lightweight power supplies are created.

The power supply is, at first glance, a rather complicated device, but if a minor breakdown occurs, then it is quite possible to repair it yourself.

Below is a standard power supply diagram. As you can see, there is nothing complicated, the main thing is to do everything one by one so that there is no confusion:

Necessary tools for repair

In order to begin repairing the power supply yourself, you should have the necessary tools on hand.

First you need to arm yourself with computer diagnostic tools:

• working power supply unit;
• post card;
• The memory stick is in working condition;
• compatible video card;
• CPU;
• multimeter;

To perform the repair itself you will also need:

• soldering iron and everything for soldering;
• screwdrivers;
• the computer is in working order;
• oscilloscope;
• tweezers;
• insulating tape;
• pliers;

Naturally, this is not so much for a complete renovation, but this is enough for home renovation.

Step-by-step instruction

So, armed with all the necessary tools, you can begin the repair:

1. First of all, you need to disconnect the system unit from the network and let it cool down a little.
2. Unscrew all 4 screws that secure the back of the computer one by one.
3. The same operation is carried out for the side surfaces. This work is done carefully so as not to touch the wires of the unit. If there are screws that are hidden under the stickers, they must also be unscrewed.
4. After the housing is completely removed, the power supply unit will need to be blown out (you can use a vacuum cleaner). There is no need to wipe anything with a damp cloth.
5. The next step is to carefully examine and identify the cause of the problem.

In some cases, the power supply fails due to the microcircuit. Therefore, you should carefully examine its details. Particular attention should be paid to the fuse, transistor and capacitor.

Often, the cause of power supply failure is swelling of the capacitors, which break due to poor performance of the cooler. This whole situation can be easily diagnosed at home. You just need to carefully examine the top of the capacitor.

swollen capacitors

A convex cap is an indicator of fracture. In ideal condition, the capacitor is a smooth cylinder with flat walls.

To fix this problem you will need:

1. Remove the broken capacitor.
2. A new, serviceable part similar to the broken one is installed in its place.
3. The cooler is removed and its blades are cleaned of dust and other particles.

To prevent your computer from overheating, you should blow it regularly.

In order to check the fuse in another way, it is not necessary to unsolder it, but rather connect a copper wire to the contacts. If the power supply starts working, then it is enough to simply solder the fuse; perhaps it was simply moving away from the contacts.

To check the functionality of the fuse, just turn on the power supply. If it burns out a second time, then you need to look for the cause of the breakdown in other parts.

The next possible failure may depend on the varistor. It is used to pass current and equalize it. A sign of its malfunction are traces of soot or black spots. If such were found, the part must be replaced with a new one.

varistor

Note! A varistor is a computer part that is checked when it is turned on, so you need to be careful and attentive. Using a similar principle, each individual part is checked: diodes, resistors, capacitor.

It should be noted that checking and replacing diodes is not a very simple task. To check them, you should unsolder each diode individually or the entire part at once. They should be replaced with similar parts with the declared voltage.

If after replacing the transistors they burn out again, then you should look for the cause in the transformer. By the way, this part is quite difficult to find and buy. In such situations, experienced professionals recommend buying a new power supply. Fortunately, such a breakdown occurs quite rarely.

Another reason for PSU failure may be related to ring cracks that break contacts. This can also be detected visually by carefully inspecting the printed strip. You can eliminate such a defect using a soldering iron by performing careful soldering, but you must be good at soldering. If you make the slightest mistake, you can damage the integrity of the contacts and then you will have to replace the entire part.

ring cracks

If a more complex breakdown is detected, then excellent technical training will be required. Also, you will have to use complex measuring instruments. But it should be noted that purchasing such devices will cost more than the entire repair.

You should know that elements that require replacement are sometimes in short supply and not only are they difficult to obtain, but they are also expensive. If a complex breakdown occurs and repair costs exceed the price compared to purchasing a new power supply. In this case, it will be more profitable and reliable to purchase a new device.

Functionality check

After the reasons that brought the power supply out of operating mode have been eliminated, it must be checked.

The most basic operation is to turn on the computer to the network. But, by the way, this can be done without connecting a PC. It is enough to connect any load to the power supply, for example a CD-ROM, after which you need to short-circuit the green and black wires in the power supply connector and turn it on.

If everything is in order, then the fan and drive LED will immediately turn on on a working power supply. And naturally, the reverse reaction of the power supply (if nothing starts working), then the cause is not eliminated.

Once the serviceability of the device is confirmed, you can begin assembling the system unit.

Before you undertake independent repair of the power supply, you need to be fairly confident in your knowledge of electrical appliances:

1. To begin with, you can read the literature, which can easily be found on the Internet, which describes in detail the causes and symptoms of power supply failure.
2. We need to study the diagram.
3. Before you begin disassembling the system unit, make sure it is unplugged. It will be better if it is completely cooled.
4. Dust and any dirt should be blown out using a vacuum cleaner or hair dryer. It is not recommended to use a damp cloth.
5. The study should be carried out one by one of all details. It is advisable to check the operation of the power supply every time.
6. If you don’t have the skills to work with a soldering iron, and you can’t do without soldering, it’s better to contact a specialist, it will cost less.
7. If spare parts and repairs are more expensive than a new power supply unit, then it is better to think about purchasing a new part.
8. Before you begin repairing the power supply, you need to make sure that the power cable and switch are in good working order.

Signs of a broken power supply

In a vacuum, a power supply failure will not occur. If signs appear that indicate its malfunction, then before starting repairs, the reasons that led to its failure must first be eliminated.

1. Poor quality of supply voltage (voltage drops).
2. Not very high quality components.
3. Defects that were made at the factory.
4. Poor installation.
5. The arrangement of parts on the power supply plate is arranged in such a way that it leads to contamination and overheating.

Signs:

1. The computer may not turn on, and if you open the system unit, you may find that the motherboard is not working.
2. The power supply may work, but the operating system will not start.
3. When you turn on the PC, everything seems to start working, but after a while everything turns off. This may trigger the power supply protection.
4. The appearance of an unpleasant odor.

A faulty power supply cannot be missed, since problems begin with turning on the system unit (it does not turn on at all) or it turns off after several minutes of operation.

If at least one of the problems is noticed, you should think about eliminating the malfunction, otherwise, the computer may completely fail, and then you cannot do without the intervention of an experienced specialist.

Main problems:

1. The most common issue that can affect the operation of the power supply is a swollen capacitor. Such a problem can only be determined after opening the power supply unit and fully inspecting the capacitor.
2. If at least 1 diode fails, then the entire diode bridge fails.
3. Burning resistors that are located near capacitors and transistors. If such a problem occurs, then you will need to look for the problem in the entire electrical circuit.
4. Problems with the PWM controller. It is quite difficult to check; for this you need to use an oscilloscope.
5. Power transistors also often fail. A multimeter is used to check them.

Note! Power capacitors tend to hold a charge for some time; therefore, it is not recommended to touch them with bare hands after the power is turned off. Also, you should remember that when the power supply is connected to the network, you do not need to touch the stove or radiator.

Repair cost

If you repair the power supply yourself and do not have the necessary tools at hand, then first of all you will have to spend money on buying them. This amount can reach from 1000 rubles to 5000 rubles.

As for the power supply itself, everything depends on the parts that have become unusable. On average, repairs can cost up to 1,500 thousand rubles.

Please note: a used power supply in good condition can cost 2000 – 2500 rubles. This applies to models for older computers. Modern PCs are equipped with more expensive power supplies.

At a service center, a similar procedure can cost about the same amount. But at the same time, you should remember that a specialist always gives a guarantee for his work.

slarkenergy.ru

How to repair a computer power supply yourself

Problems with unstable voltage in AC networks are the scourge of domestic electrical networks, which leads to the failure of many household appliances. For example, a desktop computer. Both during operation and when switched off, this device is exposed to the negative effects of power surges. The thing is that the negative impact is mainly directed at the power supply, which still works even when the computer is turned off. And that means this is the most vulnerable place. That's why it most often fails. And here many ordinary people have a question: what to do: buy a new one or repair the computer power supply with your own hands?

Power supply for computer

The question is actually posed very correctly. Everything will depend on how the computer is built. If the power supply is assembled from nameless parts (specialists usually call them non-name parts), then this is a cheap option that makes no sense to repair. It will be easier and cheaper to choose and purchase a new one. Although you can try to repair a computer power supply using it. Even if you don't succeed, it will be a good experience. So it's worth tinkering with it at your leisure.

But if your computer has a branded power supply, then replacing it with a new one will cost a pretty penny, so it makes sense to understand its configuration and circuitry and carry out the repairs yourself.

By the way, there is an easy way to check the functionality of the power supply. To do this, it must be disconnected from the motherboard. Simply disconnect the connectors of the wires leading from the block to the plateau. Connectors can be 20 or 24 pins (4 or 6). To check whether the unit is working, you need to short-circuit contacts 14 or 15 with each other (if the connector is twenty-pin) or 16 and 17 (if it is twenty-four pin). That is, green (sometimes gray) and black wires are connected to each other. Then the unit itself is connected to the network through an outlet. If the cooler fan starts working, then everything is in order, it is not the cause. We need to look for other faults.

Computer power supply in the system unit

Repair process

So, let's start with a disclaimer that will determine the root cause of the question, how to repair a computer power supply? Remember that the power supply itself, unlike the computer, operates at 220 volts. Therefore, high-capacity capacitors are installed in his circuit. They accumulate tension that can be stored for a long time.

Do-it-yourself repair of any electronic device is based on working with a soldering iron. And if you don’t have much practice, then you should abandon this idea. After all, a computer power supply unit is a responsible device, on which it depends whether the computer will work or not.

Plus, you will have to figure out the diagram as events go, because you are unlikely to find an exact diagram, even on the Internet. There are schematic diagrams, but this does not mean that it will be exactly the same in your power supply. Therefore, everything will have to be done as the repair progresses.

Internal structure of the power supply

Where to begin

First of all, you need to remove the cover and clean all the insides from dust. A thick layer of dust becomes a barrier that prevents temperature transfer from working parts. So this is also the reason for the failure of the unit.

Now pay attention to the fuse. Usually a 5 A part is installed here. This is a glass bulb with a thin metal thread running inside it. If there is no thread, then the fuse is blown and needs to be replaced. But sometimes there seems to be a thread present, so it’s worth checking the fuse. How?

• It will be necessary to solder a copper wire with a diameter of 0.18 mm to the ends of the part.
• Then plug the unit into a power outlet.
• If the cooler fan starts working, then the fault is the fuse.
• Unsolder it from the circuit and install a new one.

The first thing you need to do is clean the inside of your computer from dust.

Capacitors

Typically, power supplies contain capacitors with large capacitance. It is in them that tension accumulates. Therefore, these are the parts that most often fail (in 80% of cases).

The first thing that should catch your eye is swelling and leakage of electrolyte. If all this is available, then it is one hundred percent that the capacitor is not working.

Attention! Poor fan operation causes capacitors to swell. The thing is that the fan must cool the capacitors, which are heated due to the accumulation of voltage in them. Therefore, experts recommend periodically cleaning the fan bearings and cleaning the entire cooler.

But sometimes there are no visible defects in capacitors, so it is worth checking them with a multimeter to check the resistance. If the resistance is high (compared to the nominal value), then this indicates that there is a gap between the inner lining and the terminal. Experts call this situation a broken capacitor.

Swollen capacitors

There are also electrolytic capacitors in the power supply circuit. They can also swell, but there is no point in replacing them with new ones, because you must first find the cause of their swelling and then replace them. Usually the cause is a failure of the voltage stabilization circuit. So until you figure it out, there is no point in changing electrolytic capacitors. It won’t help, they will still swell. But repairs to computer power supplies of this type can only be carried out by a specialist; you cannot do it yourself. Plus, you will need professional measuring instruments. So the best option is to take the power supply to a workshop. In this case there is no choice.

Transistors

This is another part that can cause the PC power supply to malfunction. Pay attention to the design feature of the transistor. He has three legs:

1. Base.
2. Collector.
3. Emitter.

So, to determine whether a part is working or not, you need to ring it with a multimeter. And here you need to know how to call. Dialing can only be done in two directions:

• The base is a collector.
• Base - emitter.

Transistors in the power supply

If you change the polarity of the dial, then nothing will happen. The same applies to the direction between the collector and emitter. To correctly carry out the ringing, you need to connect the probe with the red wire to the base of the transistor, and the black wire to the collector or emitter. If the display shows an indicator within 650-800 mV, then everything is fine, the transistor is intact.

To check, you can ring the collector-emitter. Here the resistance should be infinite, the display will show one. If this transition is broken, the multimeter will emit a characteristic signal. But note that this is not necessary; other transitions also do not work.

As for diodes, these small devices are practically the same as transistors. That is, a transistor is two diodes connected in series, but with cathodes at one point. Therefore, ringing them is practically a test of the base-collector or base-emitter transition. The resistance indicators are exactly the same.

Transistor design

Rework

What is the purpose of converting a computer power supply? That is, is it possible to replace some of its parts to improve the operation of the device? Some masters try to make some changes, and thereby achieve better results. We will not go into details of all the modifications, because we are talking about independent repairs. And some of them cannot be done with your own hands.

The simplest modification is to reinstall the capacitors that are built into the power bus. They are designed for a voltage of 5 V. So, the more voltage these devices can withstand, the better. It would be nice to install capacitors rated for 10 V in their place, but they are large in size, so they may not fit on the plateau. Therefore, it is still worth choosing a capacitor with a high voltage that would fit on the plateau, for example, at 6.5 V.

Attention! Replacing a capacitor depends on its correct installation on the plateau. Therefore, pay attention to the negative output strip. It is wide, vertical and light. So, the new device must be installed in exactly the same position so that the strip ends up in the old installation location.

The main requirement when repairing a power supply with your own hands is the ability to work with a soldering iron.

Conclusion on the topic

So, if you have replaced all the failed parts, then the power supply should work. The easiest way to check this is to plug it into a power outlet. The cooler fan should spin. There is another more reliable option - check the main connectors for voltage with a multimeter. Their value should be 12 and 5 volts.

As you can see, repairing a power supply is actually a difficult process. Although if you figure it out and go through the diagram several times, changing first one device and then another, then you can already consider yourself a home craftsman. But the most important thing, as practice shows, is the ability to work with a soldering iron.

OnlineElektrik.ru

DIY computer power supply repair. Block diagram

The power supply in a personal computer is one of the most important components. These devices differ not only in power, but also in design features. Before release, all models undergo a certain standardization procedure. The main elements of the blocks can be considered a transformer, a converter, and a rectifier. Additionally, depending on the modification, various cooling and protective systems are installed on the device.

How to replace a block?

Replacing the power supply is quite simple, and you can do it yourself without any effort. To do this, a person will only need a Phillips screwdriver from the tools. The unit is located in the personal computer case at the back side, where all the connectors are located. First of all, you need to unscrew the four nuts on the panel. After this, the unit will detach from the lid of the personal computer, but it is currently impossible to remove it. This is due to the fact that the block remains connected to the motherboard, hard drive, and CD-ROM. Therefore, before removing the device, a person is obliged to disconnect all contacts that prevent this.

General device diagnostics

When a power supply breaks down, the first thing you need to do is perform a general diagnostic to understand the cause of the problem. To do this, you need to disconnect the element from the personal computer. To do this, unscrew the four nuts that hold the protective cover of the device. This can be done using a Phillips screwdriver. Next, the lid must be carefully lifted up. In order for a person to have full access to all elements of the unit, it is important to disconnect the cooler of the device after removing the panel.

It is usually fastened with four nuts, and you can also deal with them using a Phillips screwdriver. Next, you should carefully inspect all components. In particular, it is important to pay attention to dark spots. When the system overheats, black spots usually remain. After this, you can disconnect the transformer and also inspect the converter. If the integrity of the winding is not compromised, then the unit needs a more thorough check.

Repair of Asus units

Many buyers choose an Asus power supply due to its high power. On average it is approximately 500 W. The cables of the models are mainly used of the non-modular type. On average, the best power supply from Asus costs around 3 thousand rubles. In this case, rectifiers are installed next to the converters, and their throughput is quite good. They have all standard connectors.

At a voltage of 3 V, the device can withstand an average load of 24 A. Separately, the operation of the filters should also be noted. They are installed in network type housings only and are located next to the rectifiers. The main problem with the units of the above company is considered to be overvoltage of the inductor. This is caused by the fact that the threshold voltage level increases sharply. As a result, the integrity of the winding is compromised. In order to replace the inductor, the emergency power supply must be removed from the personal computer.

Next, you need to unscrew all the nuts that hold the upper U-shaped cover. After this, you don’t even have to touch the cooler. In this case, the coil can be disconnected separately. At the same time, it is held on the microcircuit by just one contact. After replacing the element, the unit must be reassembled and inserted into the personal computer.

Common problems with Samsung units

Samsung blocks are in great demand today. Modulators in almost all models are binary. Their important advantage is good signal conductivity. At the same time, the latency in the system is quite small. However, the Samsung power supply also has disadvantages. First of all, it should be noted a common malfunction that is caused by a conflict between the system and the converter. This process occurs due to the fact that the bandwidth in the device changes. In order to solve this problem, the unit converter must be replaced.

This is quite easy to do if you have a Phillips screwdriver on hand. In this case, the cooler in the unit will have to be disconnected. This way, the person will have full access to the converter. It is attached to the microcircuit using a special clamp. In order to remove it, you need to press on the small protrusions with your fingers on both sides. The converter will then be disconnected. Before installing a new model, the plate on which the part is located must be cleaned. Regular cotton wool is suitable for these purposes. Some experts additionally advise lubricating it with ethyl alcohol.

Input filter repair

Repairing computer power supplies with your own hands if the input filter breaks is quite simple. To do this, you must first extract this element. It is usually located in the device near the rectifier. In some cases, the filter is connected to the converter. In order to check its performance, it is necessary to inspect its upper part. If dark spots are visible on it, then the element has been overloaded. In this case, the person is obliged to clean all contacts and fix the filter in its original place.

Inverter Maintenance

In order to repair computer power supplies with your own hands if the inverter breaks down, you need to have a Phillips screwdriver. The above element is located near the cooler. You can disconnect it by moving the plate that is located at its base. In some cases, manufacturers install two clamps in this place that are connected to each other. In this case, the inverter is disconnected with two fingers. Repair of the device in such a situation must begin with an inspection of the base. It is a flat plate to which the regulator is attached.

If there are any defects at the base, the element will have to be completely replaced. To do this you will need to purchase a similar model. In order to secure the inductor in its previous position, you must first lift the plate up. If there were two clamps there, then before installing the inductor they are moved to the side. After this, a protective cover is screwed onto the unit, and the device is placed back on the personal computer case.

Inspection of the control controller

It is quite difficult to repair computer power supplies with your own hands if the controller breaks down. The whole problem in this case is the presence of a large number of electrodes. When the system short-circuits, the controller is unable to operate properly. In order to clean contacts, many people recommend using an eraser. At the same time, you don’t need to put a lot of effort into it. If this does not help, then the controller is completely unscrewed from the rectifier and replaced with a new one.

This can be done using a screwdriver. In this case, it is important not to damage the microcircuit, since it is located quite close and is very vulnerable to mechanical contacts. Specialists replace the controller only with the participation of cotton wool. In this case, the lower part of the element must be thoroughly wiped. Ethyl alcohol is not recommended for use in this situation.

Cooler maintenance

Repairing computer power supplies with your own hands, including replacing the cooler, is quite simple. To do this, you must first remove the side cover from the personal computer. Then the uninterruptible power supply unit is directly disconnected. Today, a wide variety of coolers are installed in it. However, they are usually mounted on the side wall. To remove the device, you need to use a screwdriver. In this case, there are usually four nuts on it.

After this, you can directly disconnect the cooler from the unit. However, it is important to ensure that its power cable does not interfere. It is best to disconnect it immediately in this situation. This can be done simply by lifting the port, which is located near the chip. After this, the cooler can be conveniently placed on the table for further work. First of all, it is important to remove the sticker, which is its additional protection. There may be a small rubber gasket underneath it. Depending on the design of the fan, it can cover the connecting rod or the rolling bearing.

In order to remove the bushing, it is necessary to remove the protective ring that holds it in place. After this, the bushing protrudes. At this stage, you need to make sure that the puck does not fall on the floor. The cooler is then cleaned with machine oil and must be reassembled in reverse order. After turning on the power supply, you need to check the operation of the fan and make sure it is working properly. If after all the above steps it makes any sounds, then the device was assembled incorrectly.

Replacing the power choke

Repairing the PC power supply by replacing the inductor can only be done using a blowtorch. In order to get to the specified part, the block must be completely disassembled. Additionally, the inverter must be disconnected. The converter is removed from the chip last. The throttle for the block should be selected from a specific series. In this case, much depends on the power of the device. The contacts begin to be soldered precisely from the microcircuit side, and then the inductor is connected to the transformer. Subsequently, if the wiring is soldered incorrectly, the contacts can be reconnected.

Inspection of the microcircuit

Before repairing a PC power supply, the microcircuit must be inspected. In general, this part is quite complex in its design. Considering this, it is necessary to treat the microcircuit with special care. First of all, experts advise inspecting the resistors that are located next to the controller. In some cases, their contacts overheat. In general, you can check the functionality of the microcircuit simply by connecting a normal model.

Radiator repair

The radiator in the unit breaks quite rarely, but such cases do occur. In this situation, it must be disconnected from the transformer. Only after this will a person be able to examine it. At this stage, only the base of the part is checked. In particular, it is necessary to inspect its platform for any defects. After this, the part is inspected from the top. If dark spots are visible on it, then the radiator has become unusable. To replace it, you need to purchase a similar product from the store. It is attached to the transformer, usually with a screw. However, much in this case depends on the manufacturer.

How to test a pulse transformer?

Repairing the unit in terms of inspecting the transformer is only possible if you disconnect the cooler in advance, since it will interfere in the future. After this, the transformer is inspected from the sides. If its contacts are dirty, then they need to be cleaned. A regular eraser is ideal for these purposes. However, alcohol-based wipes can also be used. If the specified procedure does not help in the operation of the unit, then the transformer needs to be changed.

Replacing the controller on the transformer

Replacing the controller at home is very quick. The only tool required for this procedure is a Phillips screwdriver. The controller is attached to the transformer using only one clamp. It is quite easy to remove from the safety lock, and no great physical effort is required. Next, it is important to clean the metal part and wipe it with a dry cloth. After this, it is possible to connect a new controller model. When the unit is turned on, the device should operate quietly. If any noise appears, it means that the installed element is not suitable for the block according to its parameters.

Rectifier failure

Repairs to the unit regarding faults with rectifiers are carried out only in special workshops. However, it is also not possible to replace it at home. Considering all of the above, there is no need to try to remove the rectifier from the microcircuit. All this in some cases ends simply in the block breaking. Specialists using a soldering iron and tweezers can remove this device without damaging the board.

After inspecting the rectifier, it will be possible to decide its fate in the future. As a rule, the easiest way is to simply replace it with a new one. However, in this situation, the reason for its failure is taken into account. The rectifier itself does not break, and in parallel in the block their converter and transformer also fail. All this is a consequence of a sharp increase in the maximum voltage in the network.

Problems with Aerocool blocks

Models from this company are currently actively sold out. The average cost of a power supply (market price) is around 3 thousand rubles. The power of a conventional model is around 500 W, and the device can hold a maximum load of 23 A. A common problem with these elements is considered to be the breakdown of the modulator. However, converters often fail due to overvoltage. In this case, the fans installed are usually reliable.

Blocks of the Zalman company

The Zalman company's power supplies have good reviews. Many models of this brand can boast a maximum power of 550 V. At the same time, the transformer can hold a maximum load of 25 A. A powerful power supply from Zalman costs about 3,200 rubles. In this case, rectifiers are installed broadband. In turn, coolers can most often be found without rolling bearings.

Their lubrication disappears quite quickly, and ultimately the uninterruptible power supply unit begins to operate noisily. In such a situation, it is more advisable to disassemble the cooler and replace worn parts if necessary. Burnout of the converter is also considered a common problem with the units of this company. This happens due to a banal increase in voltage in the electrical wiring of the house. As a result, the transformer inside the unit may additionally burn out.

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How to repair a computer power supply

A computer's power supply unit (PSU) is a complex electronic device that provides power to all computer devices. As a rule, the power supply has several power connectors with different output voltages designed to power certain devices.

Checking the functionality of the power supply

You can perform a preliminary check of the power supply without special instruments and without disassembling the power supply itself. The essence of the test is to check the power supply starting system, as well as checking the computer devices for possible short circuits.

Disconnect all power connectors from all devices on the system unit. To disconnect the motherboard power connector, you must first unlock it. Now manually start the power supply. To do this, you need to short-circuit two pins on the motherboard power connector with a wire or a paper clip (usually a green wire and any black one, less often there may be a gray wire instead of green). If the connector has pin markings, then the Power ON and GND pins should be shorted.

After this, the power supply should turn on, which can be checked by rotating the cooler of the power supply cooling system. If the power supply does not turn on, then it is faulty and its further repair should be entrusted to a specialist.

However, successfully turning on the power supply does not guarantee that it is working stably. In this case, first of all, it is necessary to check the system unit (PC) devices for a possible short circuit.

First connect the motherboard to the power connector and turn on the power supply; if it starts, then the motherboard is working. Now turn off the power supply and unplug the power cord. This is necessary to ensure that the power supply can be restarted manually.

Now connect other computer devices in series (hard drive, floppy drive, etc.) and turn on the power supply. If you do not find a fault, then the next step is to check the power supply itself. Well, if when you connect one of the devices, the power supply does not start, then most likely there is a short circuit in the power supply circuit of this device.

The power supply may work successfully, but the output voltage may be too low or too high, which will lead to instability of the computer. You can determine this by using a multimeter (digital voltmeter) and measuring the output voltage at the power connectors. On the multimeter, switch the handle to the position for measuring direct voltage (DCV) with a measurement limit of 20V.

Connect the black probe of the multimeter to the black wire of the power supply, this is our ground, and touch the second (red) one to the corresponding terminal of the power supply connector, that is, to all the others.

The output voltages of the power supply must be within acceptable limits: For the supply voltage +3.3V (orange wire), the permissible voltage deviation should not exceed 5% or from +3.14V to +3.46V.

For +5V supply voltage (red and blue wires), the permissible voltage deviation should not exceed 5% or from +4.75V to +5.25V.

For supply voltage +12V (yellow wire), the permissible voltage deviation should not exceed 5% or from +11.4V to +12.6V.

For a supply voltage of -12V (blue wire), the permissible voltage deviation should not exceed 10% or from -10.8V to -13.2V.

It is best to take measurements under load, i.e. when the computer is turned on.

Troubleshooting the power supply

Before troubleshooting the power supply, it must be removed from the computer. Lay the computer case on its side and unscrew all four screws securing the power supply. Carefully remove it from the case so as not to damage other computer devices and disassemble it by removing the casing. After this, remove all the dust accumulated inside using a vacuum cleaner.

Replacing the fuse

All power supplies have a similar design and functional diagram. At the input of each power supply there is a fuse, which is soldered into the printed circuit board, but there are also power supplies on which mounting sockets are installed, for the convenience of replacing the fuse. This is what needs to be checked first.

A blown fuse thread indicates either a short circuit or the power supply is operating under high load. Replace it with a similar one with the same response current or a slightly higher current (for example, if you have a 5 A fuse installed, then it can be replaced with 5.5-6 A - no more!). But, in no case should you install a fuse with a lower operating current - it will burn out immediately.

If you still encounter a fuse that is soldered into the printed circuit board. In this case, you can install a regular fuse suitable for the current by soldering a small copper wire with a diameter of 0.5-1 mm to its ends, which will act as a leg.

In the power supply circuit, after the fuse, a network filter is installed, built on a high-frequency pulse transformer, a diode bridge and electrolytic capacitors.

I would like to immediately warn you, dear readers, that if you disassemble your power supply and there are no network filter elements there, it means that you have installed a cheap and low-quality power supply in your PC and it will look something like this.

Also, transistors are installed on radiators in the power circuit of the power supply, usually there are only two of them. After which there is a circuit for generating voltage and stabilizing it.

After disassembling, carry out an external inspection of the power supply; there should be no swollen capacitors, burnt radio elements, torn or unsoldered wires, poor soldering, broken tracks on the printed circuit board and other damage, as well as missing radio elements.

The most common cause of power supply failure is simple overheating. This may be due to dust that accumulates inside or a malfunction of the cooling system. Therefore, promptly clean both the power supply and the entire computer from dust, and also periodically lubricate the cooling fans.

Replacing electrolytic capacitors

Swollen electrolytic capacitors are very easy to detect; they have a bulge at the top. Electrolyte often leaks from them, as evidenced by a characteristic drip on the printed circuit board. Such capacitors must be replaced with ones of similar capacity and supply voltage.

In this case, it is possible to replace capacitors of the same capacity with capacitors of similar capacity, but with a higher operating voltage. The main thing in this case is that the size of the capacitor allows it to be placed on a printed circuit board.

It is also important to observe polarity when replacing electrolytic capacitors. If there are a lot of swollen capacitors, then replacing them will not restore the functionality of the power supply; the reason, most likely, is different.

Also, you should not replace a charred resistor or transistor with new ones; the cause of such malfunctions usually lies in other radio elements or circuit components, so without special skills and instruments it will be problematic to discover the cause on your own. In this case, you have a direct route to the service.

The cause of the malfunction quite often is power circuits - these are transistors installed on radiators, a filter and capacitors. You can check them using special instruments or using an ohmmeter. But for this they must be desoldered.

The diode bridge (four rectifier diodes or a diode assembly) can also fail; this element can be checked without unsoldering it from the printed circuit board; use an ohmmeter or a multimeter with a diode test function for this (ohmmeter measurement limit is 2000 Ohm). When connecting the device to a diode in one position, it should show resistance (about 500 Ohms), and when connected inversely, the resistance should be maximum (tend to infinity).

Capacitors are also checked with an ohmmeter, when connected there should be no breaks or short circuits. But when checking the filter, the ohmmeter should show minimal resistance. If a faulty element is identified, it should be replaced with a similar one. Domestic analogues should not be used to replace failed radioelements.

If you managed to find the malfunction and successfully eliminate it, then after turning on the power supply, immediately check the level of all output voltages and only after that install it into the computer. If you were unable to repair your power supply yourself, then do not be discouraged; probably, the cause of its malfunction lies in the supply voltage generation circuit or in other components, which will be very difficult to identify on your own and without special devices. Also, such repairs may not be economically feasible.

Bye everyone and see you again.

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Repairing computer hardware yourself is quite a difficult task. At the same time, the user must know exactly which of all the components needs repair. It makes sense to repair a computer's power supply if it is (at a minimum) out of warranty, and also - the cost of replacement makes such repairs truly worthwhile. High-quality repairs in a service center can reach the cost of “budget” power supplies. Usually, the user can do some things himself... Provided that he has the skills to work with electrical equipment (220 Volts) and well understands the danger of mistakes in such work.

Recommendations for self-repair of computer power supplies:

1. Connection to a 220 V network of any power supply must be made through a “fast” fuse with a current of no more than 2A.
2. The first start after repair work is carried out in series with an incandescent lamp. A short circuit at the input of the device will be indicated by the glow of the lamp. Such a power supply cannot be connected to the network.
3. In the process of both diagnostics and repair, it is necessary to discharge all electrolytic containers (after each switch on/off). You need to wait 3-5 minutes, or use a 220V electric lamp - the flash will indicate that the discharge has actually been produced.
4. All repair operations are carried out with the power supply completely disconnected from the network.

It is advisable that there are no grounded objects near the workplace (such as heating radiators, pipes, etc.)

Actually, we will not “get into” the high-voltage part of the power supply circuit. Self-repair comes down to: searching for “ring” cracks; replacing power diodes (if necessary); replacing “bad” capacitors (if necessary).

In any case, repairing a computer power supply begins with removing it from the PC. Of course, this is worth doing if you are 100% sure that it is the power supply that needs to be repaired.

The body of the power supply itself is disassembled by unscrewing the self-tapping screws (screws) securing the two halves to each other. A Phillips screwdriver is used.

Note: by disassembling the power supply yourself, you damage the manufacturer's seal - which entails the loss of further warranty for this device.

Directly how the power supply is repaired and the main malfunctions are described below. Most often, failures that occur can be detected and eliminated quite simply:

• Check if the “standby” voltage (+5V SB) is present. This is the purple wire of the 24-pin (main) power supply connector. Between “black” and “purple” there should be a voltage of +5 Volts. You can check its presence before disassembling the unit case; in this case, the power supply itself must be connected to the network.

• We disassembled the power supply - look at the board. Faulty (swollen) electrolytic capacitors are common. This can be determined visually; most often it is electrolytic capacitors of not very large capacity (470-220 µF or less) that are susceptible to defects. Such a capacitor must be unsoldered from the board (to do this, it will have to be removed), and a new one must be of the same capacity and designed for the same (or higher) voltage. Attention: observe the polarity of the leads! On imported ones, the “stripe” indicates “minus”.

• The next malfunction is the failure of low-voltage diodes (12 or 5V). They can be structurally designed as assemblies of two diodes (flat housing with three terminals), or they can be installed separately.

• Checking/replacing diodes is a little more complicated than with capacitors. To check, you need to unsolder one terminal of each diode (you can also unsolder the entire part). Everyone knows how a working diode “rings”. With a direct connection, the tester will show a value (close to “0”), with a reverse connection it shows nothing (the tester itself is turned on in the “diode” mode):

• As a replacement, it is recommended to install Schottky diodes that have a similar (or higher) declared current/voltage.

• When repairing the power supply yourself, unscrew the screws of the board itself and remove it (make sure once again that the unit must be de-energized). Looking carefully at the installation, you can quickly notice the defects of “ring cracks”:

They need to be “soldered”, then everything must be assembled and turned on (perhaps everything will work).

Separately, it is necessary to say about “standby” food. As a rule, repairing the power supply by simply replacing burnt-out transistors will not yield results - the transistors burn out again, and the same ones. The transformer may also be the culprit of the breakdown. This is a scarce item that is difficult to buy and find. In rare cases, the reason for the absence of 5V “standby” voltage may be a change in the operating frequency, for which the “frequency-setting” parts are responsible: a resistor and a capacitor (not electrolytic).

Note: to desolder a part installed on the heat sink, first dismantle (unscrew) its fastening. Installation is done in the reverse order (first fastening, then soldering). Try not to disturb the insulation of the part from the heat sink (usually mica is used).

Starting the power supply: check for +5V SB. If it is there, let’s try to start the power supply (connect the “lime” wire, PS-ON, to the “black” wire, common).

At this point, the user’s capabilities for independent repairs are, one might say, exhausted.

Attention! Do not attempt to repair the power supply yourself unless you have experience in electrical engineering! After each shutdown, it is necessary to discharge the high-voltage capacitors (wait 3-5 minutes)!

Read more: “swollen” capacitors and their replacement

We hope that from the photograph it is clear which capacitors are “swollen” and which are not.

If there are several identical ones on the board (or a set of parallel connected ones), of which at least one is defective, it is better to change everything. Companies that produce reliable products: Nichicon, Rubycon. But you are unlikely to find such ones. For budget ones, we can recommend Teapo, Samsung.

When installing, it is necessary to observe polarity (operating voltage must be the same or greater than that indicated on the one being replaced).

In the photo there is a 16 Volt capacitor, 470 MicroFarad (Rubycon, the most expensive series).

Soldering technology

When installing and dismantling parts on a computer power supply board, it is recommended to use a 40-watt soldering iron. In some cases, for bulky parts (“powerful” leads), you can use a 60-watt soldering iron (but no more).

The simplest solder (such as POS-60) is suitable in this case. It is better to take it in the form of a thin wire.

Flux – not used (it is enough to have regular rosin available).

Dismantling the part:

• Heat with a soldering iron until the solder completely melts;
• Using a desoldering device (made of plastic), quickly pump out the liquid solder:

• Repeat steps 1 and 2.

A correctly soldered part easily comes out of the board on its own (no need to “press” the lead with a soldering iron).

If the capacitor is being dismantled, you can first “bite off” the protruding terminal with side cutters.

If the power element is unsoldered, you must completely unscrew the fastening screw.

Replacing the fuse

In the circuit of any power supply, the fuse goes immediately after the power outlet (in series with one of the 220 V phases). The fuses themselves, as parts, vary in current strength (that is, how many amperes it will withstand at maximum). Also, fuses are divided into “F” type (“fast”), “T” type (“thermal”).

If the fuse needs to be replaced, you must find out what rating (current) it was designed for. Also, it is advisable to know the “type”.

Replacement with a fuse with a higher rating is not allowed. Replacing F with T is the same.

Note: If you know the required “current” but not the “type”, you can install a new type “F” fuse.

Exactly. And so that there are no questions about why it burns out more often, it will still be easier to find out reliable data (both denomination and type).

If the fuse is in a glass cylindrical case, then in any case it is designed for 220V power supply. The use of other types of construction is not permitted.

What is used (devices and materials)

When repairing a computer power supply , You won’t need any “non-standard” devices or equipment:

But what is in fig. – implies that you at least know how to handle: a soldering iron, a tester (pliers, side cutters...). For professional repairs, there should have been an oscilloscope (3 MHz bandwidth is sufficient). That's just the price... (like 2-3 new power supplies).

We hope the information provided here will be useful for performing “initial” repairs. More complex operations (repairing a transformer, working with high-voltage wiring, restoring generation) can be done by professionals (who have experience specifically in repairing power supplies).

A switching power supply is not a very “simple” device; in some cases, restoration of viability is carried out by complete replacement of parts (of one or another unit). More complex, “independent” repairs do not have to be “successful” in every case...

Diode characteristics

The diode itself, as a separate element, can be one of three types: a simple diode (p-n junction), a microwave diode, and a Schottky diode (quantum). We are only interested in the last of them.

The job of a diode is to pass current in one direction (and not pass it in the other). If the voltage drop in direct connection on conventional diodes is 1 or 2 volts, then on Schottky diodes it is close to zero. The voltages obtained in a computer power supply are low (12 Volts and 5), which is why only Schottky ones are used.

You can see what the voltage drop across the diode is. The tester must be in “diode” mode (as mentioned above). If it “shows” from 0.015 to 0.7, then everything is correct. Such values ​​are typical for a Schottky diode (less is a “breakdown”).

Inside the power supply circuits, a pair of diodes is used, turning them on counter:

For positive voltage, “assemblies” are used (three-terminal, with 2 diodes in them). Single diodes (round body) - usually used to produce negative voltages. When replacing single diodes (even if one “flies”), it is recommended to replace them in “pairs”.

What is the best way to choose a replacement? If on the “rectangular” plastic case (3-pin) the brand is written:

Then, with “round” ones it will be more difficult. The stripe on the body only means “direction”.

If we know the brand of diodes, we look for the same ones, or look at the parameters (voltage, current), and look for an analogue (with the same or slightly higher value).

If we don’t know, well, you need to “download” the circuit diagram of your power supply and take a look. By the way, in the SC they also do this (but thinking and guessing what the current strength is is not a very rewarding task). Not forgetting that computer power supplies contain only Schottky diodes.

Note: installing diode assemblies/diodes with obviously high current and voltage parameters is not recommended (let’s say: it was 50 Volts 12 A, but they install 50 Volts 20 A). There is no need to do this, because: there may be a different case. In addition, there are “additional” parameters (which in a more “powerful” case differ “not for the better”).

Typical example (assemblies, low-power power supply): 12CTQ040 (40V, 12A); 10CTQ150 (150V, 10A).

Example of single diodes: 90SQ045 (45V, 9A); SR350 (50V, 3A).

Replacing the power supply fan

How to choose a new fan for PSU? It, that is, the fan, must be: with a hydraulic bearing, three-pin (3 wires in the cable), and of suitable dimensions (12cm/8cm).

It is also important that the power supply uses a low-speed “vent”, usually 1200-1400 (for 12 cm) and 1600-2000 (for 8).

When the power supply starts, not all the voltage is supplied to the fan (not 12 Volts), but, let’s say, 3-5 Volts. It is important that the fan is able to “start” at such voltages (otherwise, it will not spin up after switching on). Check the “starting voltage” of the fan, be careful.

Method of connecting the fan to the power supply:

1. Two wires (black, red) are soldered to the power supply board.
2. Two wires (black, red) are connected with a 2-pin connector to the board connector.
3. Three wires (black, red + yellow) are connected to the board using a 3-pin connector.

In the first two cases, the yellow wire - the tachometer - can be removed from the power supply housing for monitoring by the motherboard itself.

Pay attention to such a parameter as the height of the fan. If you take more than you need, the PSU case “will not close.”

When replacing, it is important that the performance of the new fan (in “liters per minute”) is at least the same as that of the old fan. Perhaps this parameter is the main one (it is usually indicated in the product description).

Thus, you can immediately “mod” the power supply by installing an equally productive, but quieter propeller (a hydraulic bearing in budget power supplies is not often included “by default”).

That's probably all that can be said about fans. Choose.

Equivalent load

The power supply, when started by “wiring”, started. Don't rush to install it on your computer. Let's try to test the power supply on an equivalent load.

The following resistors are taken:

They are called “PEV” (the brand of copper wire they are made from). You can take it at 25 watts, or at 10 (at 7.5):

The main thing here is to make a circuit of them (connecting: in parallel, in series) to get a “powerful” resistance (3 Ohms and 5-6 Ohms).

We will connect a 5-ohm load to the “12V” line, a 3-ohm load to the “5V” line. To connect to the power supply, use a Molex connector (yellow wire is 12 V):

Note: when creating an "equivalent", take into account the power that falls on each resistor (it should not exceed the value for which it is designed).

Knowing the voltage across the resistor, the power is found according to the law: voltage squared / resistance.

Example: 4 resistors of 20 Ohms - “in parallel”, the power of each is 7.5 Watts (will be used for testing the “12-volt” line).

You can also use 12V halogen light bulbs (for example: two 10 Watts in parallel).

So, having connected the equivalent load to the Molex connector, we try to turn on the power supply (“lime”/“black”, ATX connector). The cord “220 Volt” must also be “standard”.

If it turns on, wait 10 seconds. Is the block going into defense? The fan must rotate, all voltages must be in the required range (deviation of no more than 5-6% is allowed).

Actually, in such a “gentle” mode for it, any power supply should work for as long as desired.

A more powerful “equivalent” can be made. That is, the resistance in Ohms will be even lower. The main thing is not to “overdo it” (for each power supply, the maximum current is indicated):

The current through the load is equal to the voltage divided by its resistance (in ohms). Well, you already know this...

When testing, the “load” will be included in only two lines (“plus 5”, “plus 12”). This is, in general, enough. Other voltages (“minuses”) can be measured with a voltmeter (on a 24-pin plug).

Note: if you want to “test” the “+12” line with a current strength higher than 6A, do not use Molex connectors! 4-pin processor power connector (+12 V) – holds up to 10 Amps. If necessary, the load is “spread” between two connectors (processor, Molex).

Note 2: When making any connections, use a wire of sufficient cross-section (per 1 mm2 - current 10 A).

At the equivalent load, heat will be generated (thermal power is equal to electrical power). Take care of cooling (air flow). During the testing process, the first 2-3 minutes - it is better to monitor whether one of the resistors overheats.

The photo shows a “serious” approach to creating an “equivalent”.

Power supply repair

In the modern world, the development and obsolescence of personal computer components occurs very quickly. At the same time, one of the main components of a PC - the ATX form factor - is practically has not changed its design for the last 15 years.

Consequently, the power supply of both an ultra-modern gaming computer and an old office PC work on the same principle and have common methods for diagnosing faults.

The material presented in this article can be applied to any personal computer power supply with a minimum of nuances.

A typical ATX power supply circuit is shown in the figure. Structurally, it is a classic pulse unit on a TL494 PWM controller, triggered by a PS-ON (Power Switch On) signal from the motherboard. The rest of the time, until the PS-ON pin is pulled to ground, only the Standby Supply with a voltage of +5 V at the output is active.

Let's take a closer look at the structure of the ATX power supply. Its first element is
:

Its task is to convert alternating current from the mains to direct current to power the PWM controller and standby power supply. Structurally, it consists of the following elements:

• Fuse F1 protects the wiring and the power supply itself from overload in the event of a power supply failure, leading to a sharp increase in current consumption and, as a consequence, to a critical increase in temperature that can lead to a fire.
• A protective thermistor is installed in the neutral circuit, which reduces the current surge when the power supply is connected to the network.
• Next, a noise filter is installed, consisting of several chokes ( L1, L2), capacitors ( C1, C2, C3, C4) and counter-wound choke Tr1. The need for such a filter is due to the significant level of interference that the pulse unit transmits to the power supply network - this interference is not only picked up by television and radio receivers, but in some cases can lead to the malfunction of sensitive equipment.
• A diode bridge is installed behind the filter, converting alternating current into pulsating direct current. Ripple is smoothed out by a capacitive-inductive filter.

Standby power supply is a low-power independent pulse converter based on the T11 transistor, which generates pulses through an isolation transformer and a half-wave rectifier on the D24 diode, powering a low-power integrated voltage stabilizer on the 7805 chip. Although this circuit is, as they say, time-tested, its significant drawback is high voltage drop across the 7805 stabilizer, which leads to overheating under heavy load. For this reason, damage in the circuits powered from the standby source can lead to its failure and subsequent inability to turn on the computer.

The basis of the pulse converter is PWM controller. This abbreviation has already been mentioned several times, but has not been deciphered. PWM is pulse width modulation, that is, changing the duration of voltage pulses at their constant amplitude and frequency. The task of the PWM unit, based on a specialized TL494 microcircuit or its functional analogues, is to convert DC voltage into pulses of the appropriate frequency, which, after an isolation transformer, are smoothed by output filters. Voltage stabilization at the output of the pulse converter is carried out by adjusting the duration of the pulses generated by the PWM controller.

If your computer's power supply fails, do not rush to get upset; as practice shows, in most cases repairs can be done on your own. Before moving directly to the methodology, we will consider the block diagram of the power supply and provide a list of possible faults; this will significantly simplify the task.

Structural scheme

The figure shows an image of a block diagram typical for switching power supply system units.

Designations indicated:

• A – surge protector unit;
• B – low-frequency rectifier with a smoothing filter;
• C – auxiliary converter stage;
• D – rectifier;
• E – control unit;
• F – PWM controller;
• G – cascade of the main converter;
• H – high-frequency rectifier equipped with a smoothing filter;
• J – power supply cooling system (fan);
• L – output voltage control unit;
• K – overload protection.
• +5_SB – standby power mode;
• P.G. – information signal, sometimes designated as PWR_OK (necessary for the motherboard to start);
• PS_On – signal controlling the start of the power supply.

Pinout of the main PSU connector

To carry out repairs, we will also need to know the pinout of the main power connector, it is shown below.

To start the power supply, you need to connect the green wire (PS_ON#) to any black zero wire. This can be done using a regular jumper. Note that some devices may have color markings that differ from the standard ones; as a rule, unknown manufacturers from the Middle Kingdom are guilty of this.

PSU load

It is necessary to warn that without load significantly reduces their service life and can even cause breakdown. Therefore, we recommend assembling a simple load block; its diagram is shown in the figure.

It is advisable to assemble the circuit using resistors of the PEV-10 brand, their ratings are: R1 - 10 Ohms, R2 and R3 - 3.3 Ohms, R4 and R5 - 1.2 Ohms. Cooling for the resistances can be made from aluminum channel.

It is not advisable to connect a motherboard or, as some “craftsmen” advise, a HDD and CD drive as a load during diagnostics, since a faulty power supply can damage them.

List of possible faults

We list the most common malfunctions characteristic of switching power supply system units:

• The mains fuse blows;
• +5_SB (standby voltage) is absent, and also more or less than permissible;
• the voltage at the output of the power supply (+12 V, +5 V, 3.3 V) is not normal or missing;
• no P.G. signal (PW_OK);
• The power supply does not turn on remotely;
• The cooling fan does not rotate.

Test method (instructions)

After the power supply is removed from the system unit and disassembled, first of all, it is necessary to inspect it to detect damaged elements (darkening, changed color, loss of integrity). Note that in most cases, replacing the burnt part will not solve the problem; you will need to check the piping.

If none are found, proceed to the following algorithm of actions:

• check the fuse. You should not trust a visual inspection, but it is better to use a multimeter in dial mode. The reason why the fuse has blown may be a breakdown of the diode bridge, a key transistor, or a malfunction of the unit responsible for the standby mode;

• checking the disk thermistor. Its resistance should not exceed 10 Ohms; if it is faulty, we strongly advise against installing a jumper instead. The pulse current that occurs during the charging of capacitors installed at the input can cause breakdown of the diode bridge;

• We test diodes or a diode bridge on the output rectifier; there should be no open circuit or short circuit in them. If a malfunction is detected, the capacitors and key transistors installed at the input should be checked. The alternating voltage supplied to them as a result of the breakdown of the bridge, with a high probability, caused these radio components to fail;

• checking electrolytic type input capacitors begins with inspection. The geometry of the body of these parts must not be violated. After this, the capacitance is measured. It is considered normal if it is not less than declared, and the discrepancy between the two capacitors is within 5%. Also, the equalizing resistances sealed in parallel with the input electrolytes must be checked;

• testing of key (power) transistors. Using a multimeter, we check the base-emitter and base-collector junctions (the method is the same as for).

If a faulty transistor is found, then before soldering in a new one, it is necessary to test its entire wiring, consisting of diodes, low-resistance resistances and electrolytic capacitors. We recommend replacing the latter with new ones that have a larger capacity. Good results are obtained by shunting electrolytes using 0.1 μF ceramic capacitors;

• Checking output diode assemblies (Schottky diodes) using a multimeter, as practice shows, the most typical malfunction for them is a short circuit;

• checking electrolytic type output capacitors. As a rule, their malfunction can be detected by visual inspection. It manifests itself in the form of changes in the geometry of the radio component housing, as well as traces of electrolyte leakage.

It is not uncommon for an apparently normal capacitor to turn out to be unusable when tested. Therefore, it is better to test them with a multimeter that has a capacitance measurement function, or use a special device for this.

Video: correct repair of an ATX power supply.
https://www.youtube.com/watch?v=AAMU8R36qyE

Note that non-working output capacitors are the most common fault in computer power supplies. In 80% of cases, after replacing them, the performance of the power supply is restored;

• The resistance between the outputs and zero is measured; for +5, +12, -5 and -12 volts this indicator should be in the range from 100 to 250 Ohms, and for +3.3 V in the range of 5-15 Ohms.

Refinement of power supply

In conclusion, we will give some tips on improving the power supply, which will make its operation more stable:

• in many inexpensive units, manufacturers install two-amp rectifier diodes; they should be replaced with more powerful ones (4-8 amperes);
• Schottky diodes on the +5 and +3.3 volt channels can also be installed more powerful, but they must have an acceptable voltage, the same or greater;
• It is advisable to replace the output electrolytic capacitors with new ones with a capacity of 2200-3300 μF and a rated voltage of at least 25 volts;
• It happens that instead of a diode assembly, diodes soldered together are installed on the +12 volt channel; it is advisable to replace them with a Schottky diode MBR20100 or similar;
• if 1 µF capacitances are installed in the key transistors, replace them with 4.7-10 µF, designed for a voltage of 50 volts.

Such a minor modification will significantly extend the life of the computer power supply.

A computer's power supply unit (PSU) is a complex electronic device that provides power to all computer devices. As a rule, the power supply has several power connectors with different output voltages designed to power certain devices.

Checking the functionality of the power supply

You can perform a preliminary check of the power supply without special instruments and without disassembling the power supply itself. The essence of the test is to check the power supply starting system, as well as checking the computer devices for possible short circuits.

Disconnect all power connectors from all devices on the system unit. To disconnect the motherboard power connector, you must first unlock it. Now manually start the power supply. To do this, you need to short-circuit two pins on the motherboard power connector with a wire or a paper clip (usually green wire and any black, less often there may be a wire instead of green gray colors). If the connector has pin markings, then the pin should be shorted Power ON And GND.

After this, the power supply should turn on, which can be checked by rotating the cooler of the power supply cooling system. If the power supply does not turn on, then it is faulty and its further repair should be entrusted to a specialist.

However, successfully turning on the power supply does not guarantee that it is working stably. In this case, first of all, it is necessary to check the system unit (PC) devices for a possible short circuit.

First connect the motherboard to the power connector and turn on the power supply; if it starts, then the motherboard is working. Now turn off the power supply and unplug the power cord. This is necessary to ensure that the power supply can be restarted manually.

Now connect other computer devices in series (hard drive, floppy drive, etc.) and turn on the power supply. If you do not find a fault, then the next step is to check the power supply itself. Well, if when you connect one of the devices, the power supply does not start, then most likely there is a short circuit in the power supply circuit of this device.

The power supply may work successfully, but the output voltage may be too low or too high, which will lead to instability of the computer. You can determine this by using a multimeter (digital voltmeter) and measuring the output voltage at the power connectors. On the multimeter, switch the handle to the DC voltage measurement position ( DCV) with measuring limit 20V.

Connect the black multimeter probe to black The power supply wire is our ground, and touch the second (red) one to the corresponding terminal of the power supply connector, that is, to all the others.

The output voltages of the power supply must be within acceptable limits:
For supply voltage +3.3V ( orange wire ) the permissible voltage deviation should not exceed 5% or from +3.14V to +3.46V.

For supply voltage +5V ( red and blue wires ) the permissible voltage deviation should not exceed 5% or from +4.75V to +5.25V.

For supply voltage +12V (yellow wire ) the permissible voltage deviation should not exceed 5% or from +11.4V to +12.6V.

For supply voltage -12V ( blue wire) the permissible voltage deviation should not exceed 10% or from -10.8V to -13.2V.

It is best to take measurements under load, i.e. when the computer is turned on.

Troubleshooting the power supply

Before troubleshooting the power supply, it must be removed from the computer. Lay the computer case on its side and unscrew all four screws securing the power supply. Carefully remove it from the case so as not to damage other computer devices and disassemble it by removing the casing. After this, remove all the dust accumulated inside using a vacuum cleaner.

Replacing the fuse

All power supplies have a similar design and functional diagram. At the input of each power supply there is a fuse, which is soldered into the printed circuit board, but there are also power supplies on which mounting sockets are installed, for the convenience of replacing the fuse. This is what needs to be checked first.

A blown fuse thread indicates either a short circuit or the power supply is operating under high load. Replace it with a similar one with the same response current or a slightly higher current (for example, if you have a 5 A fuse installed, then it can be replaced with 5.5-6 A - no more!). But, in no case should you install a fuse with a lower operating current - it will burn out immediately.

If you still encounter a fuse that is soldered into the printed circuit board. In this case, you can install a regular fuse suitable for the current by soldering a small copper wire with a diameter of 0.5-1 mm to its ends, which will act as a leg.

In the power supply circuit, after the fuse, a network filter is installed, built on a high-frequency pulse transformer, a diode bridge and electrolytic capacitors.

I would like to immediately warn you, dear readers, that if you disassemble your power supply and there are no network filter elements there, it means that you have installed a cheap and low-quality power supply in your PC and it will look something like this.

Also, transistors are installed on radiators in the power circuit of the power supply, usually there are only two of them. After which there is a circuit for generating voltage and stabilizing it.

After disassembling, carry out an external inspection of the power supply; there should be no swollen capacitors, burnt radio elements, torn or unsoldered wires, poor soldering, broken tracks on the printed circuit board and other damage, as well as missing radio elements.

The most common cause of power supply failure is simple overheating. This may be due to dust that accumulates inside or a malfunction of the cooling system. Therefore, promptly clean both the power supply and the entire computer from dust, and also periodically lubricate the cooling fans.

Replacing electrolytic capacitors

Swollen electrolytic capacitors are very easy to detect; they have a bulge at the top. Electrolyte often leaks from them, as evidenced by a characteristic drip on the printed circuit board. Such capacitors must be replaced with ones of similar capacity and supply voltage.

In this case, it is possible to replace capacitors of the same capacity with capacitors of similar capacity, but with a higher operating voltage. The main thing in this case is that the size of the capacitor allows it to be placed on a printed circuit board.

It is also important to observe polarity when replacing electrolytic capacitors. If there are a lot of swollen capacitors, then replacing them will not restore the functionality of the power supply; the reason, most likely, is different.

Also, you should not replace a charred resistor or transistor with new ones; the cause of such malfunctions usually lies in other radio elements or circuit components, so without special skills and instruments it will be problematic to discover the cause on your own. In this case, you have a direct route to the service.

The cause of the malfunction quite often is power circuits - these are transistors installed on radiators, a filter and capacitors. You can check them using special instruments or using an ohmmeter. But for this they must be desoldered.

The diode bridge (four rectifier diodes or a diode assembly) can also fail; this element can be checked without unsoldering it from the printed circuit board; use an ohmmeter or a multimeter with a diode test function for this (ohmmeter measurement limit is 2000 Ohm). When connecting the device to a diode in one position, it should show resistance (about 500 Ohms), and when connected inversely, the resistance should be maximum (tend to infinity).

Capacitors are also checked with an ohmmeter, when connected there should be no breaks or short circuits. But when checking the filter, the ohmmeter should show minimal resistance. If a faulty element is identified, it should be replaced with a similar one. Domestic analogues should not be used to replace failed radioelements.

If you managed to find the malfunction and successfully eliminate it, then after turning on the power supply, immediately check the level of all output voltages and only after that install it into the computer. If you were unable to repair your power supply yourself, then do not be discouraged; probably, the cause of its malfunction lies in the supply voltage generation circuit or in other components, which will be very difficult to identify on your own and without special devices. Also, such repairs may not be economically feasible.

Video:

Bye everyone and see you again.