Which contacts should be made in the power supply? Why and how to run a power supply without a motherboard

When working with a stationary PC, a situation may arise in which the computer simply refuses to turn on. Using the “Power” button does nothing, and what could cause such dysfunction is also unknown. Most often, suspicion falls on the computer's power supply; if it fails, the voltage supply to the motherboard stops. How to turn on the power supply without a computer and using the “Power” button on the case? Let's figure it out.

As you know, the computer is turned on using the “Power” button, which, in turn, is connected to the motherboard. To run the power supply without a computer, we need to exclude the motherboard from this circuit using a method that I will describe below.

When performing this operation, remember that:

• It is necessary to turn off the PC and completely disconnect the power supply from the computer;
• You need to connect some kind of load to one of the external connectors of the power supply (any old hard drive or CD (DVD) player will do). Without such a load, various negative consequences are possible, in the form of the power supply refusing to start, its failure, and other undesirable dysfunctions;
• Be extremely careful when performing the following operations. Accidentally closing the wrong contacts can damage the device.

We start the power supply without a computer

To bypass the circuit using the motherboard, we need some kind of metal clip or small wire with stripped ends. Even ordinary technical tweezers may come in handy.

The green contact in the diagram is usually depicted as “PS-ON” (“Power Supply ON” - turning on the power supply), and the black one as “COM” (“Common” - common) or GND (“Ground” - grounding);

Connector diagram

• The power supply should turn on and its cooler should work.

Some craftsmen connect a full-fledged switch instead of such wiring.

Other ways to check the power supply

There are also a number of alternative ways to check the performance of the power supply.

Output voltage measurement

To check the performance of the power supply, we can measure its output voltage using a voltmeter. To do this, it is recommended to turn on the power supply as indicated above (if it turns on). And measure the indicators of a number of wires of the black and pink wires of the main 24-pin connector. In the case of black and pink wires, the indicator should be 3.3, black and yellow - 12, and black and red - 5 V. The permissible deviation should not exceed 5% in the lower or upper direction.

Checking for swelling of capacitors

The second way is to check the hardware of your power supply for the presence of swollen capacitors on the board. To do this, you need to disconnect the power supply from the PC, remove the cover from it and visually inspect all existing capacitors.

If you notice swollen capacitors, then there is a high probability that they have already exhausted their service life and need to be replaced. You need to unsolder them from your power supply and replace them with new ones of the same value.

Conclusion

To turn on the power supply without a computer, you need to use a piece of wire stripped at both ends, which is used to close pins 4 and 5 of the main connector of the power supply, as described just above. Usually this method is universal and makes it possible to understand the overall performance of a given device. If the unit does not turn on, then it is quite possible that it needs a thorough repair.

In contact with

There are times in life when it is necessary turn on the power supply without connecting it to the motherboard. There are several reasons for this inclusion. For example, check the functionality of the power supply or find out the noise level of its cooler.

Now all power supplies are of the ATX standard. Such units have several “pigtails” with SATA and Molex connectors for connecting drives, several connectors for supplying power to the video card, 4-pin or 8-pin power supply to the processor, as well as 24-pin (possibly 20-pin) power supply to the motherboard.

In addition, there is a latch key on the connector for connecting to the motherboard. So next to it there is a black wire with a hexagonal contact. If you turn the cable with the locking key down and count the fifth contact from right to left (can be labeled COM or GND), then this will be exactly it. Near this COM pin there is a green wire, in the same row. This is the only wire and can be called on the cable as PS-ON. If in doubt, turn the cable again with the locking key down and count the fourth contact from right to left.

This method of finding the desired contact is universal and does not depend on the number of contacts on the cable. Whether it's 24-pin or 20-pin. By the way, there are power cables with detachable 4-pin connectors. They are also labeled 20+4-pin.

It may be that you have a Chinese power supply from an unknown manufacturer and the green wire is missing. Don't worry. The order of the wires does not change from this.

Now you need to take a small piece of wire or paperclip, expose its edges. One end is connected to the fourth pin contact, and the other to the fifth pin contact. Although you can connect another contact to any of those that have a black wire. For example, to the third pin contact.

Now you can turn on the power supply by connecting it to the network. The power supply will work immediately. You will know this by the rotation of its cooler. If the power supply has a controlled cooling system, in which the cooler does not rotate at low loads, then try connecting a cooler from the system unit or an optical drive. This will also help ensure that the power supply is in working order.

How to turn on a computer power supply without a computer?

It can work in this mode for no more than 5 minutes. After all, this mode of operation, without load, should be short. So before connecting to the network, still connect either a cooler or a disk drive, or a hard drive. Check what worries you and turn it off. Read more interesting tips in the section

Many computer enthusiasts have a question: “How to turn on the power supply without a computer?” This need is caused by various reasons, most often we are talking about checking the performance of cathode lamps or new coolers.

Why such difficulties?

It is simply necessary to turn on the power supply without the computer in case of repair, because if you constantly turn the computer off and on, this will negatively affect the PC components due to premature failure of the batteries. In addition, any experiments with the computer may result in unstable operation of the operating system.

First start

As computer wisdom says, if you can find a PC power supply, how to turn it on is even easier to understand. All modern computer units comply with ATX (a special international standard). Thus, the 20-pin connector has a contact that is responsible for the active state of any such unit. We are talking about the fourth contact from the left (you need to count from the fastening latch). Most often, the contact we need is green. You should try to connect this wire to ground (i.e. any black wire). It is most convenient to use the adjacent, 3rd contact. If everything is done correctly, the power supply will instantly come to life and the cooler will make noise.

How to turn on the power supply without a computer: details

ATX standard devices can output the following voltages: 3.3, 12 and 5 V. In addition, they have good power (from 250 to 350 W). But here’s the question: “How to turn on a computer power supply?” Above, we have already, so to speak, outlined the procedure in a nutshell, and now let’s try to understand it in more detail.

It was easier in the old days

Interestingly, older units that are AT standard could be run directly. With the ATX standard, everything is much more complicated. However, the solution to a huge problem comes down to a small wire that needs to be connected in a certain way. We have already described how to turn on the power supply without a computer, but we ask you to disconnect all the wires going to the motherboard, hard drives, drives and other components. Better yet, remove the element we need from the system unit and work away from it.

Another important point that should not be overlooked: do not let the power supply run idle. This way you can shorten his life. You definitely need to give it a workout. For this purpose, you can connect an old hard drive or fan. As already noted, you will need black and green contacts to start. However, remember that some manufacturers, for unknown reasons, refuse to follow the established color coding. In this case, it is advisable to first carefully study the pinout. If your knowledge allows, you can make a special button to turn on the power supply.

Strange computer power problems: PC stops turning on

First, let's check the presence of a primary power supply of ~220V at the input of the power supply. Among the reasons for the absence are a malfunction of the surge protector, socket, plug, or cable break. The problem may also lie at the source. On the back of many units there is a power switch - this may also be faulty or turned off.

When primary power is supplied, even if the computer is turned off, there is a voltage of +5V at the power supply output (if everything is working properly). This can be checked by testing the contacts of the power supply connector with a tester. We are interested in pin 9, which has a purple wire (+5VSB).

Often the motherboard has an LED indicating standby voltage. If it is active, both standby and primary nutrition are present.

If the computer still does not turn on, we look for other sources of the problem. We will look at the most common reasons below.

1. Open circuit in the power button. To check this, use tweezers to close the contacts responsible for turning on the power supply on your motherboard, or start the power supply outside the system unit (we described in detail above how to turn on the power supply without a computer).

2. Short circuit that occurs at the output of the power supply. Try disconnecting all devices from power and temporarily removing all adapters from their slots. In addition, you should disconnect all USB devices. You can also deactivate the 4-8-pin power connector for the processor Power Connector +12V.

3. Malfunction of the motherboard or power supply. If only the motherboard is connected to the power supply, but it does not turn on, it is likely that the unit itself is faulty. As for the malfunction of the motherboard, which makes it impossible to turn on the computer's power supply, we note that this is theoretically possible, but in practice it is extremely rare. To check this, turn on without connecting the connector to your motherboard. If the power supply turns on, it is the motherboard that is faulty.

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

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

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

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

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

The main elements in the composition voltage converter are:

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

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

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

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

Main causes of malfunctions

The causes of malfunctions in the power supply can be:

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

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

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

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

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

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

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

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

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

ATX computer power supply repair

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

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

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

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

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

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

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

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

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

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

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

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

conclusions:

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