DIY repair of a power supply for a computer

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

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, triggered by the 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 alternating current from the mains to direct current 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.

Video (click to play).

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. This primarily concerns the switching transistors T2 and T4, which are installed on aluminum radiators. 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.

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):

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 the 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.

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, perhaps, such 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.

Read also: DIY brick oven repair

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 that 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.

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.

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 for diagnostics or, as some "craftsmen" advise, an HDD and a 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:

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

Before you start repairing a power supply unit, you need to understand how it works, know its main components. Repair of power supplies should be carried out extremely careful and remember about electrical safety during work. The main units of the power supply unit include:

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

The inlet filter is used for interference suppressiongenerated by the power supply in electrical circuit. At the same time, it performs a protective function during abnormal operating modes of the power supply unit: protection against excess current value, protection against voltage surges.

When the power supply unit 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 by the motherboard and equal to 3 volts.

After pressing the power button on the PC, the PS_ON value becomes zero and the starting the main converter... The power supply begins to generate basic signals to the computer board and protection circuits. In the event of a significant excess of the voltage level, the protection circuit interrupts the operation of the main driver.

To start the motherboard, a voltage of +3.3 volts and +5 volts are applied to it simultaneously, from the power device, to form the PW_OK level, which means food is normal... Each wire color in the power device corresponds to its voltage level:

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

The power supply device basically works on the principle 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 the transistors in the power unit is controlled by a specialized microcircuit PWM controller. When a signal arrives at the transistor, it opens, and a current arises on the primary winding of the pulse transformer. As a result of electromagnetic induction, voltage appears on the secondary winding. By changing the pulse duration, the opening time of the key transistor is regulated, and hence the signal magnitude.

The controller included in the main inverter starts up from the enabling signal motherboard. The voltage goes to the power transformer, and from its secondary windings goes to the other nodes of the power source, which form a number of required voltages.

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

A filter is placed at the end of each power supply line. Its purpose is to remove parasitic pulsations formed by transient processes of transistors. It consists, like any mains filter, of an electrolytic capacitor and inductance.

Before proceeding directly to diagnostics of the computer power supply device, you need to make sure that the problem is in it. The easiest way to do this is to connect knowingly good block to the system unit.Troubleshooting a computer power supply can be carried out according to the following method:

In case of damage to the power supply unit, you must try to find a manual for its repair, a circuit diagram, data on typical malfunctions.
Analyze the conditions under what conditions the power source worked, whether the electrical network is working properly.
Using your senses to determine if there is a smell of burning parts and elements, whether there was sparking or flash, listen to whether extraneous sounds are heard.
Assume one malfunction, highlight the defective item. This is usually the most time consuming and painstaking process. This process is even more time consuming if there is no electrical circuit, which is simply necessary when searching for "floating" faults. Using measuring devices, trace the path of the fault signal to the element on which there is a working signal. As a result, to conclude that the signal disappears at the previous element, which is inoperative and requires replacement.
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 case of the system unit. After that, the fastening screws are unscrewed and the protective cover is removed. Having blown and cleaned from dust, they begin to study it. Practical repair DIY computer power supply can be presented step by step as follows:

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

When restoring the PC power supply, you will need to use various kinds of devices first of all, it is a multimeter and preferably an oscilloscope. With the help of the tester, it is possible to carry out measurements for a short circuit or an open circuit of both passive and active radioelements. The performance of the microcircuit, if there are no visual signs of its failure, is checked using an oscilloscope. In addition to measuring equipment for repairing a PC power supply, you will need: a soldering iron, a suction for solder, washing alcohol, cotton wool, tin and rosin.

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

The PSU case is connected to the common wire of the printed circuit board. The measurement of the power section of the power supply is carried out with respect 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.

The resistors are checked by comparing the readings of the tester and the markings applied to the resistance case or indicated on the diagram. The diodes are checked by a tester, if it shows zero resistance in both directions, then a conclusion is made about its malfunction. If it is possible to check the voltage drop across the diode in the device, then you can not solder it, the value is 0.5-0.7 volts.

Capacitors are checked by measuring their capacity and internal resistance, which requires a specialized ESR meter. When replacing, note that low internal resistance (ESR) capacitors are used. Transistors ring up the performance of p-n junctions or, in the case of outfield, the ability to open and close.

The next stage of checking the power supply occurs under load. First, the presence of a standby voltage is checked for this, the output is loaded with a load of the order of two amperes. If the duty officer is in order, the power supply is turned on by shorting PS_ON, after which the output signal levels are measured. If there is an oscilloscope, it looks like a ripple.