A power supply is a hardware component of a PC that supplies power to internal devices. He receives it from the home electrical network and converts alternating current into direct current, which is necessary for the elements of the computer. And also it regulates the voltage inside the computer network to the working level, which allows the machine to work stably and not overheat. It is an integral part of any PC and must work properly so that other components function reliably. Therefore, if the power supply does not start, the user needs to check it, and if necessary, repair or replace.
All about power supplies
AC network current cannot be directly supplied to the PC, because its components use direct current energy and you need to perform the rectification process first. This transition determines the main task of the power supply unit (PSU) as an AC rectifier.
The source is designed in such a way that ensures regulatory voltage to all nodes of the PC. To do this, it distributes power over different cables with an operating voltage. For example, a DVD hard drive connector provides 5 volts for electronic components and 12 volts for its drive motor.
PC components have different connections, but each source has all the necessary connectors for standard assembly. Especially important: the unit must have so many plugs for hard disks and CD / DVD drives so that additional drives can be easily installed.
Most office PCs have a small 300W model. An adapter for a PC with gaming support should provide at least 400 watts of power because powerful processors and fast graphics cards require a lot of power. In this case, a malfunction may occur when the power supply starts up and shuts down immediately.
If several video cards work in a PC, then a model with a power of 500 or 650 watts may be required. 1,000 watts devices are currently sold. But they are rarely applicable. If you purchase a low-power unit, the computer may fail, for example, during games or watching videos. This is because the corresponding PC components consume a lot of energy. Overheating is the main reason why the power supply does not start.
ATX DC Source Description
The ATX unit is an energy converter. It converts the alternating current (AC) supplied by the energy supply company to direct current (DC) with the required voltage level sufficient for the components of the PC, which corresponds to 110-115 or 220-230 volts.
This conversion is performed using processes:
- switching;
- straightening;
- filtering.
Many PCs have a unit called SMPS or pulse. When the switching power supply does not start and it is necessary to test its operation, users need to strictly comply with safety measures and measures to protect against electric shock. The PSU contains hazardous voltages and currents. Inside there are capacitors that accumulate energy and can hit a person with an electric current, so the unit must be repaired only by qualified personnel.
Recommendations and protective measures in case the ATX power supply does not start:
- The user can easily find the source on the system unit by seeing the input to which the cord is connected without opening the computer.
- If you turn off and remove the PSU, it will look like a metal box with a fan inside and several cables attached to it.
- The average user is not recommended to disconnect the power supply, it is better to leave it in the case.
PSU: computer hardware component
PS, P / S or PSU are abbreviations for power supply. Below is a list of the items that come with the PSU:
- Power cord to the computer.
- Housing to prevent dust from entering the PSU.
- A fan for cooling and venting.
- Switch for changing voltage.
- Cable packages located on the front internal panel of the PSU. They connect to the computer motherboard and internal components. Therefore, if the power supply does not start, the motherboard is the first device that will stop working.
- Connectors for disks.
- The motherboard connector is a 24-pin ATX, which, when connected, provides power to it.
- Input voltage selector
The ATX function block provides standby current of +5 V, 720 mA through the purple wire to the motor contact. This current is also supplied to the PCI slots, even when the computer is turned off and damaged. Therefore, when the power supply does not start, there is a duty room. Therefore, it is recommended that when the PSU is turned off, wait 30 seconds before starting work inside the system unit in order to take appropriate precautions against electrostatic discharge.
Diagnosing Power Problems
Power problems can be difficult to diagnose, especially if the user does not know what to look for. Here are some tips on how to quickly identify a malfunction if the power supply does not start and how to fix this malfunction.
A bad source can be a prerequisite for many PC problems. Experience can help a technician diagnose problems caused by a faulty source, which beginners usually ignore.
Any intermittent problem may be caused by a faulty source. Common symptoms when a computer power supply does not start:
- Power failure.
- Spontaneous reboot or intermittent blocking during stable operation.
- Memory errors.
- HDD and fan do not spin.
- Overheating due to a disabled fan.
- Frequent shutdowns that cause a system restart.
- Electric shocks that are felt when touching the chassis.
There are also some obvious tips that should answer the question of why the power supply does not start. These include:
- A system that is completely dead, nothing happens in it when the PC is turned on.
- Smoke that appears when you turn on the PC.
Another way to check the power supply is to use special software. It allows you to detect changes in temperature or performance, it will show how much energy is supplied to which components, which will help solve the problem faster.
PSU electrical check
First make sure that the computer is connected to the mains via an outlet. If necessary, you can use a lamp or hairdryer to make sure that the electrical outlet is working. In some cases, there is a switch on the PSU, make sure that it is turned on. Sometimes a smaller red switch may be installed on the unit to select the type of voltage.
The power supplies of the latest releases sometimes have an electric filter that prevents the computer from restarting after a short circuit. To fix this malfunction, simply unplug the power cord from the computer, then press and hold the power button for several seconds to discharge the stored energy and reset the protection.
The power supply works correctly if the voltage in the wires matches the parameters:
- blue + 11.20 V;
- yellow + 11.20 V;
- purple + 5.20 V;
- orange + 3.33 V;
- red + 5.20 V;
- white + 5.20 V;
- gray + 5.20 V.
The power sources are not designed to operate in standby mode, so the voltages may vary slightly from the table below, and for this reason, the source should only work this way for a short time. Voltage by pin numbers:
- No. 1 - 3.3 V;
- No. 2 - 12 V;
- No. 3, 5, 6, 7 - GND;
- No. 4 - nutrition;
- No. 8 - 5 V;
- No. 9, 10 - 5 V;
- No. 11, 12 - 3.3 V;
- No. 13, 15, 17 - GND;
- No. 14, 16 - 5 V;
- No. 18 - PW-OK;
- No. 19 - 5 V;
- No. 20 - 12 V.
For current power supplies, the Power / On control line is usually green.
Simplified ATX Verification Method
If the ATX power supply does not start, then check the correct operation for compliance with its voltage specifications of the manufacturer. To perform these tests, use a screwdriver to open the box, a cable to bypass the power. In this case, use a simple paper clip and one multimeter to perform the necessary measurements. First of all, you need to take certain precautions before opening the PSU case. The source must be disconnected from the mains and the power button on the rear panel is off.
First you need to open the box with a screwdriver and find the PSU connector, consisting of 24 (20 + 4) contacts. After finding it, disconnect it from the motherboard. The next step is to find the green wire, called PS_ON (PowerSupply ON), which is connected to the common black PSU cable. Using a jumper with a clip, the green wire is connected to any black wire of the connector, after which the source will be artificially switched on without the need to connect the base board. After that, connect the power cable to the mains and press the button on the rear panel to put it on. In order to make sure that the bridge is made correctly, turn on the power source, and if the fan rotates and drives air, then everything is done correctly.
Now you need to take measurements, for which they use a multimeter. The red and black connectors are located in the position of the tension measurement: black connector for COM and red for V Hz.
The rotary switch is located in the DC voltage measuring area at position 20, as it will measure 3.3 V, 5 V and 12 V.
Polarity Brief Note
If the power supply does not start the first time, during the test it is necessary to ensure the polarity of the measurements with the multimeter. They place the black measuring wire of the multimer in any common cable, and the red one in sequence in the cable of different colors that are in the PSU connector. Measure the voltage for compliance with the passport values specified by the manufacturer. All voltages to be determined are constant. PSU wires are color coded.
The test leads are also color coded: red for positive (+) and black for negative (-). To check the output voltage on the motherboard, place the black test lead on the black pin, and the red one on the Power_Good (P8-1) terminal of the AT, Baby AT and LPX power supplies, as well as pin 3 on the 20-pin ATX connectors. It should show from +3 to +6 volts DC. If the user does not see this voltage, then the unit is faulty.
Any voltage within 10 percent of the specified is acceptable for testing purposes. Some problems cannot be detected by direct measurement, so stock availability for replacement is crucial.
Audit with Advanced Tester
The following instructions apply only to a specialized tester for ATX Coolmax PS-228 power supplies, or for any other similar tester with an LCD screen.
Important: this process is considered complex, the user must carefully follow the instructions below.
Necessary time: testing a PSU with a test device for a power supply usually takes about 30 minutes or a little more for beginners.
Algorithm of actions:
- Read important safety tips for PC repair. Checking the power supply includes working with high voltage electricity, a potentially hazardous activity. Safety should be a major concern during block inspection.
- Open the case by turning off the computer, disconnecting the power cord and everything connected to the outside of the computer.
- Move the disconnected unit to a place where you can easily work, for example, on a table. The user does not need a keyboard, mouse, monitor or other external peripheral devices.
- Disconnect the power connectors of each internal device on the side panel. An easy way to make sure that each power connector is disconnected is to remove the set of power cord that comes from the PSU. Each group of cables must end with one or more power connectors. There is no need to disconnect disconnect data cables or other cables that are not connected to the PSU.
- Group all power cables and connectors for easy testing. When organizing power cables, it is recommended to disconnect them and remove them from the computer case as far as possible. This will allow you to easily connect the power connectors to the advanced tester.
- Ensure that the power supply voltage switch located on the rear panel is correctly configured for the country of residence. In the USA, this switch should be set to 110 V / 115 V, and in Russia to 220/230.
- Connect the 24-pin ATX power connector and the 4-pin ATX power connector on the motherboard in the tester for PC power supplies. Depending on the source, there may not be a 4-pin connector on the motherboard, but there may be 6 or 8 pins. If there is more than one type, simply connect alternately with the 24-pin main power connector.
- Connect the power supply to an electrical outlet and turn on the switch. Some units do not have a switch on the rear panel. If the source that is being tested does not work, just connect the device to supply power. Press and hold the tester on / off button for PC power supplies. The user should hear that the fan inside the source starts to work.
Some versions of the advanced Coolmax PS-228 PSU tester do not require a constant press of the power button. The fact that the fan is running does not mean that the power source is correctly supplying power to other devices. If the power supply fan does not start during testing, even if the source is in good condition, it may be burned out and must be checked separately.
The LCD of the extended tester for sources should be turned on, and the user will see the test numbers for all indicators. If the voltage indicates “LL” or “HH” or if the LCD does not light up, the PSU is not functional, so you will have to replace it.
Peripheral Power Connector Monitoring
If you need to check individual connectors, continue testing the PSU. Verification Algorithm:
- Turn off the switch on the power supply panel and disconnect it from the outlet.
- Connect the socket of the tester socket to the corresponding SATA connector with the 15-pin modification of Molex. You cannot connect more than one of these peripheral connectors at the same time, otherwise the tester may be damaged.
- The two connectors on the motherboard should remain connected for these tests with the other connectors.
- Connect the source, and then turn on the button on the panel.
- The indicators marked +12 V, + 3.3 V, and +5 V correspond to the voltage supplied through the connected peripheral power connector and must be lit properly. Otherwise, a replacement power supply is required.
- The SATA connector provides +3.3 V DC. You can see the voltage supplied by the various connectors by looking at the output pin tables of the ATX connectors.
- Repeat this process for other power connectors one at a time, except for the connector on the motherboard, which remain connected to the tester all the time.
- After the tests are completed, turn off the power supply, disconnect the tester cables, and then connect the internal devices of the PC to the source.
- After the PSU has been tested or replaced with a new one, you can turn on the PC again.
Replacing a failed device
If the computer’s power supply does not start, the fan does not work, and testing shows that the source does not provide the correct output voltage, it should be repaired or replaced. Since the PSU does not contain many user serviceable parts, for most people this means replacing. Before starting, make sure that the new source has the correct form factor and rated power. Power in watts should be the same as the old model. It is better to choose one size larger in power when replacing.
BP replacement is quite simple:
- Disconnect all cables from the back of the device.
- Open the case and disconnect all drive cables and cables that power the motherboard.
- Check the wire to the processor fan. This is usually a small pair that can break if pulled too much. On some computers, it is also necessary to turn off the switch.
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After the user has successfully completed all the tests and determined that the power supply is working, and the computer does not start, then most likely the power supply goes into defense. In this case, it is recommended to disconnect all devices (CD-ROM, FDD, HDD, sound, video, memory) from the unit and the motherboard in turn, thereby establishing the source of the breakdown.