DIY atx power supply repair

In detail: do-it-yourself atx computer power supply repair from a real wizard for the site my.housecope.com.

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 proceeding directly to the technique, we will consider the block diagram of the power supply unit and provide a list of possible malfunctions, this will greatly simplify the task.

The figure shows an image of a block diagram typical for pulsed power supplies of system units.

Switching power supply unit ATX

Indicated designations:

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

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

Power supply plugs: A - old (20pin), B - new (24pin)

To start the power supply, it is necessary to connect the green wire (PS_ON #) to any zero black wire. This can be done using a conventional jumper. Note that for some devices the color coding may differ from the standard one, as a rule, unknown manufacturers from China are guilty of this.

It is necessary to warn that turning on impulse power supplies without load will significantly reduce their service life and may even cause damage. Therefore, we recommend assembling a simple block of loads, its diagram is shown in the figure.

Video (click to play).

Load block diagram

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

It is undesirable to connect a motherboard as a load during diagnostics or, as some "craftsmen" advise, an HDD and CD drive, since a faulty power supply unit can damage them.

Let's list the most common malfunctions characteristic of pulsed power supplies of system units:

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

After the power supply is removed from the system unit and disassembled, first of all, it is necessary to inspect for the detection of damaged elements (darkening, changed color, violation of integrity). Note that in most cases, replacing a burnt-out part will not solve the problem; a piping check will be required.

Visual inspection allows you to detect "burnt" radioelements

If these are not found, we proceed to the following algorithm of actions:

If a faulty transistor is found, then before soldering a new one, it is necessary to test its entire strapping, consisting of diodes, low-resistance resistances and electrolytic capacitors. We recommend changing the latter to new ones with a large capacity. A good result is obtained by shunting electrolytes using 0.1 μF ceramic capacitors;

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

Diode assemblies marked on the board

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

It is not uncommon for an outwardly normal capacitor to be unsuitable during testing. 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. <>

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

Capacitors with disturbed case geometry

the resistance is measured between the outputs and zero, 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.

In conclusion, we will give some tips for improving the power supply unit, which will make it work more stable:

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

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

Very interesting to read:

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

On the other hand, if the power supply generates a voltage that goes beyond the permissible limits, then this can cause the failure of important and expensive components.

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

The ATX circuit of the power supply consists of 2 nodes - a mains voltage rectifier and a voltage converter for a computer.

Mains rectifier is a bridge circuit with a capacitive filter. At the output of the device, a constant voltage of 260 to 340 V is generated.

The main elements in the composition voltage converter are:

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

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

The reasons for faults in the power supply can be:

power surges and fluctuations;
poor quality product manufacturing;
overheating associated with poor fan operation.

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

Before starting the repair, you must finally make sure that it is the power supply that is faulty. In this case, you must first check the functionality of the mains cable and the mains switch... After making sure they are in good working order, you can disconnect the cables and remove the power supply from the case of the system unit.

Before re-enabling the power supply unit autonomously, it is necessary to connect the load to it. To do this, you need resistors that are connected to the corresponding terminals.

First you need to check motherboard effect... To do this, you need to close two contacts on the power supply connector. On a 20-pin connector, this would be pin 14 (the wire that the Power On signal goes through) and pin 15 (the wire that matches the GND pin - Ground). For a 24-pin connector, this would be pins 16 and 17, respectively.

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

The next step in identifying faults is a thorough inspection of all elements. Particular attention must be paid to electrolytic capacitors. The reason for their breakdown may be a severe temperature regime. Defective 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 a capacitor does not indicate a malfunction. If, by indirect indications, 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.

A faulty power supply can also be associated with faulty low voltage diodes. To check, you need to measure the resistance of the forward and reverse transitions of elements with 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 find such defects, you need to look very carefully on the printed circuit board. To eliminate such defects, it is necessary to use careful soldering of the cracks (for this you need to know how to properly solder with a soldering iron).

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

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

The wire diameter required for a given current can be found in the tables. For the 5A fuse used in the ATX power supply circuit, 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 above considered the most simple malfunctions of a computer power supply.

One of the most important elements of a PC is the power supply, if it fails, the computer stops working.
The computer power supply is a rather complex device, but in some cases it can be repaired by hand.

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 - an ATX power supply - is practically has not changed its design for the last 15 years.

Consequently, the power supply unit of both the ultra-modern gaming computer and the old office PC work on the same principle and have common troubleshooting techniques.

A typical ATX power supply circuit is shown in the figure. Structurally, it is a classic pulse unit on the TL494 PWM controller, which is 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
mains rectifier:

Its task is to convert AC from the mains to DC to power the PWM controller and the 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 result, 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 unit is connected to the network.
Next, a noise filter is installed, consisting of several chokes (L1, L2), capacitors (C1, C2, C3, C4) and a counter-winding choke Tr1... The need for such a filter is due to the significant level of interference that the impulse unit transmits to the power supply network - this interference is not only captured by television and radio receivers, but in some cases can also lead to incorrect operation of sensitive equipment.
A diode bridge is installed behind the filter, which converts alternating current into pulsating direct current. The ripple is smoothed out by a capacitive-inductive filter.

Further, a constant voltage, present all the time the ATX power supply is connected to the outlet, goes to the control circuits of the PWM controller and the standby power supply.

Standby power supply - this 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, supplying a low-power integrated voltage regulator on the 7805 microcircuit. high voltage drop across the 7805 stabilizer, which under heavy load leads to overheating. For this reason, damage to the circuits powered from the standby source can lead to its failure and the subsequent impossibility of turning 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, the change in the duration of voltage pulses at their constant amplitude and frequency. The task of the PWM unit, based on the specialized TL494 microcircuit or its functional analogs, is to convert the constant voltage into pulses of the appropriate frequency, which, after the isolation transformer, are smoothed by the output filters. The voltage stabilization at the output of the pulse converter is carried out by adjusting the duration of the pulses generated by the PWM controller.

An important advantage of such a voltage conversion scheme is also the ability to work with frequencies significantly higher than 50 Hz of the mains. The higher the current frequency, the smaller the dimensions of the transformer core and the number of winding turns are required. That is why switching power supplies are much more compact and lighter than classic circuits with an input step-down transformer.

A circuit based on the T9 transistor and the following stages is responsible for turning on the ATX power supply. At the moment the power supply is switched on to the network, a voltage of 5V is supplied to the base of the transistor through the current-limiting resistor R58 from the output of the standby power supply, at the moment the PS-ON wire is shorted to ground, the circuit starts the TL494 PWM controller. In this case, the failure of the standby power supply will lead to the uncertainty of the operation of the power supply startup circuit and the probable failure of switching on, which has already been mentioned.

The main load is borne by the output stages of the converter.First of all, this concerns the switching transistors T2 and T4, which are installed on aluminum heatsinks. But at high load, their heating, even with passive cooling, can be critical, so the power supplies are additionally equipped with an exhaust fan. If it fails or is very dusty, the probability of overheating of the output stage increases significantly.

Modern power supplies are increasingly using powerful MOSFET switches instead of bipolar transistors, due to the significantly lower resistance in the open state, providing a higher efficiency of the converter and therefore less demanding on cooling.

Video about the computer power supply device, its diagnostics and repair

Initially, ATX computer power supplies used a 20-pin connector (ATX 20-pin). Now it can only be found on outdated equipment. Subsequently, the increase in the power of personal computers, and therefore their energy consumption, led to the use of additional 4-pin connectors (4-pin). Subsequently, the 20-pin and 4-pin connectors were structurally combined into one 24-pin connector, and for many power supplies, a part of the connector with additional pins could be separated for compatibility with older motherboards. Image - DIY atx computer power supply repair

The pin assignment of the connectors is standardized in the ATX form factor as follows, according to the figure (the term "controlled" refers to those pins on which the voltage appears only when the PC is turned on and is stabilized by the PWM controller):

Despite its apparent power, the personal computer is fragile. To disable any part, just careless handling of it is enough. For example, do not clean the system unit and its components. As a result, a lot of dust forms on the parts, which negatively affects the operation of the device as a whole.

One of the most important components of a PC is the power supply. It is he who distributes electricity to the system unit and controls the voltage level. Therefore, the breakdown of this device can be attributed to one of the most unpleasant. Nevertheless, everyone can do the repair and fix the problem with their own hands.

The most critical situation is when the computer does not respond to the power button... This means that important points were missed that could indicate an imminent breakdown. For example, an unnatural sound during operation, a long turn-on of the computer, an independent shutdown, etc. Or maybe similar malfunctions were noticed, but it was decided not to resort to repairs.

In addition to the most critical moments, there are several signs that help identify problems in the operation of the computer power supply:

The occurrence of various errors when turning on the PC.
Sudden computer restarts.
Increasing the volume of coolers (small fans).
Various errors when the PC is turned on.
Stopping the hard drive or some coolers.
Loud beeping from the system unit (indicates overheating).
Electric shock when touching the cabinet.

Such signs indicate the need for an early repair, which can be done by hand. However, there are also more serious problemsclearly indicating a serious malfunction. For instance:

"Screen of death" (blue screen when the device is turned on or working).
The appearance of smoke.
No reaction to inclusion.

Most people, when such problems arise, turn to a repairman for a repair. Typically, a computer technician advises purchasing a new power supply and then replacing the old one. Nevertheless, with the help of repairs, you can "reanimate" an inoperative device with your own hands.

To completely solve the problem, you need to understand why it could appear. Most often, the computer's power supply fails for three reasons:

Voltage drops.
Poor quality of the product itself.
Inefficient operation of the ventilation system leading to overheating.

In most cases, such malfunctions lead to the fact that the power supply does not turn on or stops working after a short time. In addition, the above problems can negatively affect the motherboard. If this happened, then do-it-yourself repairs will not be enough here - it will be necessary to change the part to a new one.

Less often, malfunctions in the computer's power supply occur due to the following reasons:

Poor software (poor OS optimization has a bad effect on the operation of all components).
Lack of cleaning of components (a large amount of dust makes the coolers run faster).
A lot of unnecessary files and "garbage" in the system itself.

As mentioned above, the power supply is a rather fragile thing. Nevertheless, it is very important for the computer as a whole, so this component should not be ignored. Otherwise, repairs are inevitable.

The power supply in the computer is responsible for distributing and converting electrical current. The fact is that each element in a PC needs its own voltage level. In addition, AC power is used in electrical circuits, and computer components operate on DC. Therefore, the device of the power supply is quite specific and you need to know it for do-it-yourself repairs.

In each power supply unit there are 9 important components:

Without at least an approximate idea of the structure of the power supply, it is impossible to fully carry out an independent repair.

Before you start solving a problem in a computer with your own hands, you must think about your own safety... Repairing such a device is a dangerous undertaking. Therefore, first of all, you need to work thoughtfully and without haste.

For greater safety, there are several important rules to keep in mind:

Work only with the power supply off. Despite the banality of the advice, this is a very important point. No one is immune from the "fool's syndrome", so it is better to check once again that everything is turned off, and only then start repairs.
To preserve the components and also avoid "fireworks", it is recommended to install a 100 watt light bulb instead of a fuse. If the light remains on when the power supply is turned on, then the network has shorted somewhere. If it lights up and immediately goes out, then everything is in order.
Power capacitors are energized especially for a long time. Therefore, even after disconnecting the power supply from the network, you should not immediately get down to work.
It is better to check the operation of the device away from flammable substances, since there is a risk of short circuit and "fireworks" sparks.

To make repairing a power supply unit simple but effective, each home craftsman will need certain tools to work. All these products can be easily found at home, asked from neighbors / friends, or purchased in a store. Fortunately, they are inexpensive.

So, for renovation you will need the following tools:

Soldering station with built-in power regulation or several soldering irons, each of which is designed for a certain power.
Solder and flux for soldering components.
To remove solder - braid or suction.
Several screwdrivers with different tips.
Multimeter.
Side cutters (devices for cutting plastic "clamps" that hold the wires together).
100 watt light bulb.
Tweezers (for removing small components).
Alcohol or refined gasoline.
An oscilloscope may be required (if the cause of the problem is not determined).

First you need disassemble the power supply... To do this, you only need a screwdriver and accuracy. When unscrewing the bolts, you do not need to shake the PSU in order to quickly fix the problem. Careless handling of it can lead to the fact that do-it-yourself repairs will be simply useless.

For the correct formulation of the "diagnosis", it is necessary to conduct an initial diagnosis, as well as a visual inspection of the device. Therefore, first of all, you need to pay attention to the fan of the power supply.If the cooler cannot spin freely and gets stuck in a certain place, then this is clearly the problem.

In addition to the fan of the product, you should also inspect the entire device. After a long service life, a lot of dust accumulates in it, which has a negative effect and hinders the normal operation of the power supply unit. Therefore, it is imperative to clean the product from dust accumulation.

Also, some products fail. due to voltage surges... Therefore, it is necessary to carry out a visual inspection for burnt parts. This sign is easy to identify by swollen capacitors, darkening of the textolite, carbonized insulation or broken wires.

Finally, it is worth moving on to the most important point - do-it-yourself BP repair. For convenience, the entire process will be presented in the form of a list. Therefore, it is recommended not to "jump" from one point to another, but act in a specific order:

It so happens that outwardly everything is in order: the components are not melted, there are no cracks or contact violations. What is the problem then? It is best to carefully examine all the details again. It is possible that a malfunction was missed due to carelessness. If no problems were detected during the secondary inspection, then in 90% of cases the malfunction lies in standby power supply or in the PWM controllerusing wide pulse modulation.

To fix the standby voltage problem, you need to know the basics of how the power supply works. This PC component works almost always. Even when the computer itself is turned off (not disconnected from the network), the unit operates in standby mode. This means that the power supply unit sends 5 volt “standby signals” to the motherboard so that when the PC is turned on, it can start the unit itself and other components.

At system startup, the motherboard checks the voltage for all elements. If everything is in order, it is formed feedback signal "Power good" and the system starts up. If there is a lack or excess of voltage, the system start is canceled.

This means that first of all, on the board, you need to check the presence of 5 V on the PS_ON and + 5VSB pins. When checking, the absence of voltage or its deviation from the nominal value is usually revealed. If the problem is PS_ON, the problem is in the PWM controller. If there is a malfunction with contact + 5VSB, then the problem lies in the electric current conversion device.

It is also useful to check the PWM itself. True, for this you need an oscilloscope. To check, you need to unsolder the PWM and use an oscilloscope to check the contacts by ringing (OPP, VCC, V12, V5, V3.3). For better ringing, the check must be carried out relative to the ground. If the resistance between ground and any of the contacts (on the order of several tens of ohms), then the PWM must be replaced.

Self-repair of the power supply is a rather complicated process, which will require the necessary tools, initial knowledge of BP operationas well as neatness and attention to detail. Nevertheless, each person, with the proper approach, can repair the unit, despite its complex structure. Therefore, it should be remembered that everything is in your hands.

In our difficult times, in times of crisis, one main job is no longer enough in order to live with dignity, not needing money, not looking into my pocket every time with regret, and not thinking how can I make it to my next paycheck. What way can you find out of this situation? Most people who do not have in-depth knowledge in any field are limited in their choices in looking for a part-time job. But fortunately, you and I, radio amateurs, already have certain skills, which, as it turned out, can do a good job for us in a crisis. I'm talking about the repair of electronic equipment. Well, how, the majority of self-taught enthusiasts will say, will I repair the equipment when it is now mostly on SMD element base, or even on BGA?I also thought about how well it was in the 70s and 80s of the last century, most of the trained radio amateurs could perform the basics of the work of a radio mechanic, or, in other words, a telemaster. Indeed, in order to carry out most of the work on soldering the output radio components, which are soldered into the holes in the boards, you do not need to have a soldering station, let alone a BGA machine.Someone will say why these conversations, technologies have long gone ahead, and the previous level of installation of radioelements cannot be returned. Fortunately, this does not apply to all modern technology, and there is still widespread electronics in use, which is found in every home, in which non-surface mounting is still used. Most of the trained radio amateurs, I think, have already guessed that I now mean ATX format computer power supplies.Indeed, in them, if you do not take into account the relatively complex circuits, with an active PFC, only output parts are used there, not for surface mounting, and these are practically all power supplies with a power below 450 watts. I agreed in personal correspondence with the director of one of the buying-up services, about repairing their power supplies at home. They have accumulated about 100-200 pieces of them, and there is no one to fix it.But not because of a lack of qualified personnel, of course. It is not cost-effective to simply engage a service engineer to fix the power supplies, if at this time he can fix, for example, a laptop. There, the figures for profitability are of a completely different order. Therefore, we quickly came to an agreement and found a common language with the director, especially after it became clear that he himself is involved in the repair of equipment, and knows all these needs firsthand. In the future, I had the idea to share my experience in repairs with the readers of this site. With this article, we begin a series of articles devoted to the basics of repairing ATX computer power supplies.Okay, enough of the lyrics, let's get down to business. So, they brought you a patient, you know about him, only that he is not a worker. What is the first thought that comes to mind for an unprepared person? It is necessary to check this power supply, and connect it to the computer for this. So this is absolutely not the correct idea. At best, your computer will not start, or it will malfunction, at worst, if your standby voltage is too high (hereinafter referred to as the duty officer), you run the risk of burning the motherboard, and possibly something else, from the fact that connected to it. How can we not do it? ATX power supplies provide the ability to start the power supply without the computer's motherboard. To do this, we need to close two contacts called PS-ON and GND.Green (PS-ON) wires are suitable for them, sometimes the Chinese confuse it, and let it be gray, while according to the correct marking, the output of the Power-good connector, (P.G.) or otherwise Power-good, is indicated in gray. We will return to it later. You can close them with any paper clip or wire, the wire, if it is stranded, and you are going to use it regularly, it is better to tin it. Especially original people close these contacts with a piece of millimeter tubular solder)), everything is just for your taste, any conductive object with low resistance will do. What if you took the power supply in your hands, and you doubt whether the Chinese, gray and green colors have been confused in your case? Remember a simple rule, the PS-ON pin is always next to the three GND pins that are together.So, you have found a paperclip, and are ready to short-circuit the PS-ON and GND contacts with it. But there is no need to rush, there is one caveat, first you need to check if we have +5 Volts on the purple wire relative to the black GND. This contact is called + 5VSB, or the standby voltage output (watchdog). If we have 5 volts, we can close the PS-ON and GND contacts. If the power supply makes a little noise, the cooler starts to rotate, then the preliminary test of the power supply has passed.What are our actions now? And now we need to make sure if we have a voltage of 5 volts relative to ground, black wire, relative to ground, black wire, (GND), on the gray Power-good wire, (P.G.) called power good.If 5 volts are present, it is very likely that the power supply is working properly and will work stably as part of a computer. This means that all its output voltage is normal. What we need to be convinced of now. There are three main supply voltages in the power supply, on the lines giving out high current, these are +3.3, +5, +12 volts. Accordingly, these are orange, red and yellow colors of the wires. But in the power supply there is also an output of -5, -12 volts, these are the white and blue colors of the wires. They give out little power.The tolerance for the main supply voltages of +3.3, +5, +12 volts is 5%, for the rest -5, -12 volts, 10%. So, if the voltage measured with a multimeter relative to the ground on these wires is within the tolerances, this power supply can be considered conditionally good and connected for testing to the assembly or the system unit. For regular testing, it is better to get a separate assembly, for this purpose I use assembly 478 socket, with built-in video, and indication of the LED lighting up, the presence of a standby voltage installed on the motherboard. If the assembly starts when you press the PC power button, then you need to leave it for some time to drive, test, and make sure that our power supply is stable. To turn on the assembly, I use a special device made from an old mouse and connectors that are connected to the motherboard.So, how to test the power supply that came into our hands for the first time, we learned, but what if the power supply does not start with us? But we will analyze this in the following articles devoted to the repair of ATX power supplies.Especially for the site Schemes and Radio Engineering - AKV.Self-repairing a computer power supply is a rather complicated matter. Having taken up this, you should clearly understand which of the components needs repair. Also, it should be understood that if the device is under warranty, then after any intervention, the warranty card will immediately expire.If the user has little skills in working with an electrical appliance and is sure that he will not make mistakes, then you can safely take on such work. Remember to be careful when working with an electrical appliance.The power supply is the most important and required component of any system unit. He is responsible for the formation of voltage, which allows you to provide power for all PC units. Also, its important function is to eliminate current leakage and parasitic currents when pairing devices.To create a galvanic isolation, a transformer with a large amount of winding is required. Based on this, a computer requires a very high power and it is natural that such a transformer for a PC should be large and heavy.But due to the frequency of the current that is required to create the magnetic field, much fewer turns are required on the transformer. Thanks to this, when using the converter, small and light power supplies are created.Power Supply - at first glance, a rather complicated device, but if a not particularly serious breakdown occurs, then it is quite possible to repair it yourself.Below is a typical power supply circuit. As you can see, there is nothing complicated, the main thing is to do everything one by one so that there is no confusion:In order to start self-repairing a power supply unit, you should have the necessary tools at hand. First, you need to arm yourself with devices for computer diagnostics:

working power supply unit;

post card;

memory bar in working order;

compatible type of video card;

CPU;

multimeter;

For the very same repair, you will need more:

soldering iron and everything for soldering;

screwdrivers;

the computer is in working order;

oscilloscope;

tweezers;

insulating tape;

pliers;

knife;

Naturally, this is not so much for a perfect repair, but this is enough for home repairs.

swollen capacitors

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

To eliminate this breakdown you will need:

Extract broken capacitor.
In its place a new serviceable part similar to the broken one is installed.
Cooler is removed, its blades are cleaned from dust and other particles.

To avoid exposing your computer to overheating, it should be purged regularly.

In order to check the fuse in another way, it is not necessary to unsolder it, but rather connect the copper core to the contacts. If the power supply unit starts to work, then it is enough just to solder the fuse, perhaps it just moved away from the contacts.

To check the fuse is working, 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 details.

The next breakdown option may depend on the varistor. It is used to pass current and equalize it. Signs of its malfunction are traces of carbon deposits or black spots. If such were found, the part must be replaced with a new one.

varistor

It should be noted that checking and replacing diodes is not an easy task. To check them, each diode should be evaporated separately or the entire part at once. They should be replaced with similar parts with the stated 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 hard enough to find and buy. In such situations, experienced craftsmen recommend buying a new PSU. Fortunately, such a breakdown is rare.

Another reason for the breakdown of the power supply unit may be associated with annular cracks that break the contacts. This can also be detected visually by carefully examining the printed strip. You can eliminate such a defect with a soldering iron, after performing a thorough soldering, but you must be good at soldering. With the slightest mistake, you can break the integrity of the contacts and then you will have to change the entire part as a whole.

ring cracks

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

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

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

The most elementary 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 unit, 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 the drive LED on the working power supply will immediately turn on. And naturally, the reverse reaction of the power supply unit (if nothing started working), then the cause has not been eliminated.

After the serviceability of the device is confirmed, you can start assembling the system unit.

Before undertaking an independent repair of the power supply, you need to be confident enough in your knowledge of electrical appliances:

To start you can read the literature, which can be easily found on the Internet, where the causes and symptoms of a power supply breakdown are described in detail.
We need to study the scheme.
Beforethan to start disassembling the system unit, make sure that it is disconnected from the network. It will be better if it is completely chilled.
Dust and any dirt must be blown out with a vacuum cleaner or hair dryer. It is not recommended to use a damp cloth.
Study all the details should be carried out in turn. It is advisable to check the power supply every time.
If you don't have the skills to work with a soldering iron, but soldering is indispensable, it is better to contact a specialist, it will be cheaper.
When, 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.
Before, how to start repairing the power supply, you need to make sure that the power cable and switch are in good working order.

A power supply malfunction will not occur from scratch. If there are signs that indicate its malfunction, then before starting the repair, you must first eliminate the causes that led to its failure.

Poor quality supply voltage (voltage drops).
Not very high quality components Components.
Defects, which were approved at the factory.
Bad installation.
Location of parts on the plate of the power supply unit is located in such a way that it leads to contamination and overheating.

The computer may not turn on, and if you open the system unit, you can find that the motherboard is not working.
PSU can and work, but the operating system does not start.
When turning on the PC everything seems to start working, but after a while everything turns off. The protection of the power supply may be triggered.
The appearance of an unpleasant odor.

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

Major problems:

The most common momentthat can affect the operation of the power supply is the swelling of the capacitor. A similar problem can be determined only after opening the power supply unit and completely inspecting the capacitor.
If at least 1 diode fails, then the entire diode bridge also fails.
Burning resistors, which are located near capacitors, transistors. If such a problem occurs, then it will be necessary to look for the problem in the entire electrical circuit.
Problems with the PWM controller. It is quite difficult to check it, for this you need to use an oscilloscope.
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, it should be remembered that when the power supply is connected to the network, you do not need to touch the stove or radiator.

If you carry out an independent repair of the power supply and do not have the necessary tools at hand, then first of all you will have to spend money on their purchase. This amount can reach from 1000 rubles to 5000 rubles.

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

Video (click to play).

In a service center, a similar procedure can cost about the same amount. But at the same time, it should be remembered that a specialist always gives a guarantee for his work.