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Performance personal computer(PC) depends not least on the quality of the power supply (PSU). If it fails, the device will not be able to turn on, which means that the computer’s power supply will have to be replaced or repaired. Whether it's a modern gaming computer or a weak office computer, all power supplies work on a similar principle, and the troubleshooting technique is the same for them.

Operating principle and main components

Before you begin repairing a power supply, you need to understand how it works and know its main components. Repair of power supplies should be carried out extremely carefully and remember about electrical safety while working. The main components of the power supply include:

  • input (network) filter;
  • additional stabilized signal driver 5 volts;
  • main driver +3.3 V, +5 V, +12 V, as well as -5 V and -12V;
  • line voltage stabilizer +3.3 volts;
  • high frequency rectifier;
  • voltage generation line filters;
  • control and protection unit;
  • block for presence of PS_ON signal from the computer;
  • voltage driver PW_OK.

The filter located at the inlet is used for interference suppression, generated by BP in ​ electrical circuit. At the same time, it performs a protective function during abnormal operating modes of the power supply: protection against overcurrent, protection against voltage surges.

When the power supply is connected to a 220-volt network, a stabilized signal with a value of 5 volts is supplied to the motherboard through an additional driver. The operation of the main driver at this moment is blocked by the PS_ON signal generated motherboard and equal to 3 volts.

After pressing the power button on the PC, the PS_ON value becomes zero and starting the main converter. The power supply begins to produce the main signals that go to the computer board and protection circuits. If the voltage level is significantly exceeded, the protection circuit interrupts the operation of the main driver.

For start motherboard simultaneously, from the power supply, a voltage of +3.3 volts and +5 volts is supplied to it to form the PW_OK level, which means nutrition is normal. Each wire color in the power supply corresponds to a different voltage level:

  • black, common wire;
  • white, -5 volts;
  • blue, -12 volts;
  • yellow, +12 volts;
  • red, +5 volts;
  • orange, +3.3 volts;
  • green, PS_ON signal;
  • gray, signal PW_OK;
  • purple, standby food.

The power supply is based on the principle of pulse width modulation(PWM). The mains voltage converted by the diode bridge is supplied to the power unit. Its value is 300 volts. The operation of transistors in the power unit is controlled by a specialized PWM controller chip. When a signal arrives at the transistor, it opens and primary winding pulse transformer current arises. As a result of electromagnetic induction, voltage also appears on the secondary winding. By changing the pulse duration, the opening time of the key transistor, and therefore the magnitude of the signal, is regulated.

The controller included in the main converter starts from the enabling signal motherboard. The voltage enters the power transformer, and from its secondary windings it goes to the remaining nodes of the power source, which form a number of necessary voltages.

The PWM controller provides output voltage stabilization by using it in a circuit feedback. As the signal level on the secondary winding increases, the feedback circuit reduces the voltage at the control pin of the microcircuit. In this case, the microcircuit increases the duration of the signal sent to the transistor switch.

Before you proceed directly to diagnosing a computer power supply, you need to make sure that the problem lies with it. The easiest way to do this is by connecting known good block to the system block. Troubleshooting in the computer power supply can be done using the following method:

  1. If the power supply is damaged, you should try to find a manual for its repair, a circuit diagram, and data on typical faults.
  2. Analyze the conditions under which the power source worked, whether the electrical network is working properly.
  3. Using your senses, determine whether there is a smell of burning parts and elements, whether there was a spark or flash, listen to whether you can hear any extraneous sounds.
  4. Assume one fault and highlight the faulty element. This is usually the most time-consuming and painstaking process. This process is even more labor-intensive if there is no electrical diagram, which is simply necessary when searching for “floating” faults. Using measuring instruments, trace the path of the fault signal to the element on which there is a working signal. As a result, we can conclude that the signal disappears on the previous element, which is non-working and requires replacement.
  5. After repair, it is necessary to test the power supply with its maximum possible load.

If you decide to repair the power supply yourself, first of all it is removed from the system unit case. Afterwards, the fastening screws are unscrewed and the protective casing is removed. After blowing it off and cleaning it from dust, they begin to study it. Practical repair The computer power supply can be presented step by step as follows:

  1. Visual inspection. With him Special attention is given to blackened areas on the board and elements, appearance capacitors. The top of the capacitors should be flat, the bulge indicates its unusability, and there should be no leaks at the bottom at the base. If there is a power button, it would be a good idea to check it.
  2. If the inspection does not raise suspicions, then the next step is to test the input and output circuits for the presence of a short circuit (SC). In the presence of a short circuit, a broken semiconductor element in the circuit with the short circuit is detected.
  3. The mains voltage is measured on the capacitor of the rectifier unit and the fuse is checked. If there is a voltage of 300 V, proceed to the next step.
  4. If there is no voltage, the fuse burns, the diode bridge and key transistors are checked for a short circuit. Resistors and protective thermistor for open circuit.
  5. The presence of standby voltage, stabilized five volts, is checked. Statistics show that when a power supply device does not turn on, one of the most common reasons is a malfunction of the standby power supply circuit, even though the power elements are working.
  6. If stabilized five volts are present, the presence of PS_ON is checked. When the value is less than four volts, the reason for the low signal level is sought. Typically, PS_ON is formed from the standby voltage through a pull-up resistor with a nominal value of 1 kOhm. The supervisor circuit is checked, first of all, for compliance in the circuit with the capacitance values ​​of the capacitors and resistor values.

If the reason is not found, the PWM controller is checked. To do this you will need a stabilized 12 volt power supply. On board the leg of the microcircuit is turned off, responsible for the delay (DTC), and the source power is supplied to the VCC leg. An oscilloscope looks for the presence of signal generation at the terminals connected to the collectors of the transistors, and the presence reference voltage. If there are no pulses, an intermediate stage is checked, most often assembled on low-power bipolar transistors.

Typical faults and checking elements

When restoring the PC power supply, you will need to use various kinds of devices First of all, this is a multimeter and preferably an oscilloscope. Using the tester, it is possible to measure short circuits or open circuits of both passive and active radio elements. The performance of the microcircuit, if there are no visual signs of its failure, is checked using an oscilloscope. Except, measuring technology To repair a PC power supply, you will need: a soldering iron, a solder vacuum, cleaning alcohol, cotton wool, tin and rosin.

If your computer's power supply does not start, possible malfunctions can be presented in the form of typical cases:

  1. The fuse in the primary circuit blows. The diodes in the rectifier bridge are broken. The separating filter elements ring for a short circuit: B1-B4, C1, C2, R1, R2. Breakage of varistors and thermistor TR1, short-circuited transitions power transistors and auxiliary Q1-Q4.
  2. Constant voltage five volts or three volts is too low or too high. There are malfunctions in the operation of the stabilizing circuit; microcircuits U1 and U2 are checked. If it is not possible to check the PWM controller, then the microcircuit is replaced with an identical one or an analogue.
  3. The output signal level differs from the operating level. Malfunction in the feedback circuit. The PWM chip and the radio elements in its wiring are to blame; special attention is paid to capacitors C and low-power resistors R.
  4. There is no PW_OK signal. The presence of the main voltages and the PS_ON signal is checked. The supervisor responsible for monitoring the output signal is being replaced.
  5. There is no PS_ON signal. The supervisor microcircuit and the wiring elements of its circuit burned out. Check by replacing the microcircuit.
  6. The fan does not spin. Measure the voltage supplied to it, it is 12 volts. Ring the thermistor THR2. Measure the resistance of the fan leads for a short circuit. Carry out mechanical cleaning and lubricate the seat under the fan blades.

Principles of measuring radioelements

The power supply housing is connected to a common wire printed circuit board. The power part of the power supply is measured relative to the common wire. The limit on the multimeter is set to more than 300 volts. In the secondary part there is only a constant voltage not exceeding 25 volts.

Checking resistors is carried out by comparing the readings of the tester and the markings applied to the resistance body or indicated on the diagram. The diodes are checked with a tester; if it shows zero resistance in both directions, then a conclusion is made that it is faulty. If it is possible to check the voltage drop across the diode in the device, then you don’t have to solder it, the value is 0.5-0.7 volts.

Capacitors are checked by measuring their capacitance and internal resistance, which requires a specialized ESR meter. When replacing, be aware that capacitors with low internal resistance (ESR) are used. Transistors call on p-n performance transitions or in the case of field ones, the ability to open and close.

Checking a repaired power supply

After the ATX unit has been repaired, it is important to properly turn it on for the first time. At the same time, if not all problems have been resolved, the repaired and new components of the device may fail.

The power supply can be started autonomously, without using computer unit. To do this, the PS_ON contact is bridged with the common wire. Before switching on, a 60 W light bulb is soldered in place of the fuse, and the fuse is removed. If the light bulb starts to shine brightly when turned on, then there is a short circuit in the unit. If the lamp flashes and goes out, the lamp can be unsoldered and a fuse installed.

The next stage of checking the power supply occurs under load. First, the presence of standby voltage is checked; for this, the output is loaded with a load of about two amperes. If the duty station is in order, the power supply is turned on by closing PS_ON, after which measurements of the output signal levels are made. If you have an oscilloscope, you can see the ripple.

Cases of failure of power supplies in a computer are not uncommon. The reasons for this are:

1. Voltage surges in the electrical network;

2. Poor workmanship, especially for cheap power supplies and system units;

3. Unsuccessful design and circuit solutions;

4. Use of low-quality components in manufacturing;

5. Overheating of elements due to poor placement of the system unit, contamination of the power supply, or stopping of the cooling fan.

What are the “symptoms” of a faulty power supply in a computer?

Most often this complete absence signs of life of the system unit, that is, nothing buzzes, the indication LEDs do not light up, there are no sound signals.

In some cases, the motherboard does not start. At the same time, fans may spin, indicators may light up, drives may make sounds, and HDD, but nothing appears on the monitor screen.

Sometimes, when turned on, the system unit begins to show signs of life for a few seconds and immediately turns off due to the overload protection of the power supply.

In order to finally verify that the power supply is faulty, you need to open the right cover of the system unit, viewed from the rear. Pull out the main plug of the main power supply connector, which has 20 or 24 pins, from the motherboard socket, and connect the contacts with the green (sometimes gray) and the nearest black wire. If the power supply starts up, then most likely the motherboard is to blame.

The startup of the power supply can be determined by the rotation of the power supply fan, if it is working properly, and the clicking of the drives, but for reliability it is better to check the voltage at the connector. Between contacts with black and red wires - 5V, between black and yellow - 12V, between black and pink - 3.3V; between black and purple - 5V standby voltage. Minus on black, plus on colored ones. In order to make sure that the power supply is running, it is enough to measure one of the voltages, except for the “standby” 5V on the purple wire.

Sometimes users start looking for a fuse. Don't look, there aren't any outside. There is one inside, but changing it in most cases is not only useless, but dangerous and harmful, as this can lead to even bigger problems.

If it turns out that the power supply is faulty, then in most cases it is better to replace it, but it is also possible if it is economically feasible.

When purchasing a new power supply, you must first of all take into account the power, which should not be less than the previous one. It is also necessary to pay attention to the output connectors so that it is possible to connect all devices of the system unit, although necessary cases Connection problems can be solved using adapters. You can read about how to choose a power supply of the right quality.

Do I need to repair the power supply myself? If you do not have at least basic knowledge and skills in the field of electronics, definitely not. Firstly, you most likely will not be able to do this, and secondly, it is dangerous to life and health if you do not follow the safety rules.

For those who have decided to start repairing the power supply, there is an opportunity to familiarize yourself with my personal experience and thoughts on this matter.

A breakdown in the power supply is indicated not only by the inability to turn it on. The smell of burnt insulation or other foreign odors from the system unit, a sudden shutdown of the computer and extraneous noise indicate a breakdown of the power supply.

The simplest option for diagnosing failures of this type is to turn on the device with a known good component. The remaining methods require the ability to use a multimeter, and for repairs, also possession of a soldering iron and the ability to read circuit diagrams.

That is, do-it-yourself repair PSU is the lot of radio amateurs who are familiar with capacitors, diode bridges and transformers firsthand. But even in this case, repairs are not always justified. The cost of some components is higher than the price of the unit itself. Naturally, when doing repairs in a workshop, you will also have to pay for the work of the master.

The most common causes of breakdowns

The design of a power supply unit from an electrical engineering point of view is quite simple, and not many factors can damage it. Let's look at the most common of them:

  1. Voltage fluctuations in the electrical network damage the primary power circuits. Without periodic maintenance, the operating parameters of components change and they are less able to withstand even minor voltage fluctuations.
  2. Low quality of components and production. Relatively simple design The power supply is easy to manufacture. This opens up opportunities for manufacturers of junk power supplies at minimal prices. Such products use uncalibrated transistors, and the designers neglect protection components. Therefore, it is better to buy more expensive products from well-known manufacturers.
  3. Power overloads often happen when computer hardware upgrades are made by non-professionals. The total power of all system components exceeds the operating parameter of the power supply unit, and it fails.
  4. An abundance of dirt and dust in the power supply housing. Along with preventive maintenance of the cooling system, the power supply should also be cleaned of dust. Its excess can lead to short circuits and overheating. And the radio components used in the power supply, in case of violation temperature regime change their characteristics.

Moreover, as the operating temperature increases, the rated power of the power supply drops and it becomes more vulnerable to both incoming voltage transfers and overload by the sum of the powers of consumer devices.

Therefore, along with regular maintenance, you should leave a small reserve of power in the power supply.

DIY repair

Some power supply failures can still be eliminated without special knowledge and skills. But for this you will still need at least a soldering iron, a tester, electrical tape and a utility knife. When repairing and diagnosing, extreme care should be taken to avoid accidental electric shock.

Situation one

When the power supply does not turn on, and there is no output voltage (measured between any black and green wire), then you should check the capacitors (1) and transistors of the primary circuit (2). The former may be swollen, and the latter may be punctured. You should also check the fuses (3).

Situation two

If it is difficult to determine the malfunction, you should check the voltage on the capacitors of the rectifier assembly. In working condition it is 310 V, and if it is not, then you need to check all the components of the rectifier.

Situation three

The fan does not spin. If its axis is not clogged with dirt and is lubricated, then you should check the supply voltage, which should be 12 V. The absence of voltage most likely indicates a breakdown in the diode assembly of the rectifier. You should check the serviceability of components only by removing them from the board.

→ Thanks for the tip, I soldered everything, everything works. I have one last question left. I will put this discharge indicator on a regular gas lighter for the kitchen. And I have this question. There's absolutely simple circuit, power from the 18650 battery is supplied to a high-voltage transformer, the output is an arc, which will actually ignite the gas. Everything is like everyone else who made such lighters. And my question is this. At the moment of formation of a high-voltage arc, the current consumed by this transformer is approximately 3A. I want to put a button without a latch in the gap of the positive power wire to close the power supply. In this case, do I need to install a button rated for 3A or, taking into account the fact that the voltage from the battery is only 4 volts, I can get by with a button less power? At 0.5 or 1A. The power contact closures will be short-term, no longer than 3 seconds. Thank you. I'd appreciate any advice.