In detail: do-it-yourself step-by-step repair of a computer power supply from a real wizard for the site my.housecope.com.
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 large 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:
Video (click to play).
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.
VIDEO So, armed with all the necessary tools, you can start repairing:
Primarily , you need to disconnect the system unit from the network and let it cool down a little.All 4 screws are unscrewed one by one, that secure the back of the computer.The same operation is carried out for the lateral surfaces. This work is done carefully so as not to touch the wires of the block. If there are screws that are hidden under the stickers, they also need to be unscrewed.After the case has been removed completely , The PSU will need to be blown out (you can use a vacuum cleaner). You don't need to wipe anything with a damp cloth.The next step there will be careful consideration and finding the cause of the problem.In some cases, the power supply unit fails due to the microcircuit. Therefore, you should carefully examine its details. Special attention should be paid to the fuse, transistor and capacitor.
Often, the cause of a breakdown of a power supply is swollen capacitors, which break down due to poor performance of the cooler. This whole situation is easily diagnosed at home. It is enough just to carefully examine the top of the capacitor.
swollen capacitors
A convex lid is an indicator of fracture. In ideal condition, the condenser 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 by 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.
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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. Before than 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 moment that 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 perform 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.
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.
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.
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.
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.
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.
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;
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;
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:
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 suppression generated by the power supply in
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.
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
The controller included in the main inverter starts up
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.
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, determine if there is a smell of burning parts and elements, if there was sparking or flash, listen to if 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.
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 disconnected which 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.
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.
VIDEO VIDEO
After the ATX unit is repaired, it is important to correctly turn it on for the first time. At the same time, if not all the problems have been eliminated, the failure of the repaired and new units of the device is possible.
The power supply device can be started autonomously, without using a computer unit. For this, contact PS_ON is bridged with common. Before switching on, a 60 W bulb is soldered in place of the fuse, and the fuse is removed. If, when turned on, the light starts to shine brightly, then there is a short circuit in the unit. In the event that the lamp flashes and goes out, the lamp can be desoldered and a fuse installed.
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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.
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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.
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.
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.
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.
VIDEO
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 regulator, 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 circuit 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
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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.
Video (click to play).
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):
