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This article was co-written by Luigi Oppido. Luigi Oppido is the owner and operator of Pleasure Point Computers in Santa Cruz, CA. He has over 25 years of experience in general computer repair, data recovery, antivirus and upgrade.
This article has been viewed 5,010 times.
In the process of diagnosing problems on a computer, the power supply is often forgotten. However, testing the power supply first can save you a lot of trouble in troubleshooting. If your computer shows a blue screen of death (BSOD: Blue Screen of Death), a failing hard drive, or simply won’t boot, you probably have a power supply problem. Do the quick checks below before buying any expensive new hardware.
Steps
Check if the power is on
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Turn off the computer. After the computer powers off (or fails to turn on), slide the switch behind the power supply and unplug the computer.
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Open the case. Disconnect the power cable from the components inside the case. Trace each cable leading from the power supply to the other components to ensure that all are properly disconnected.
- Make a note of which cables are plugged in so you can connect them when you reassemble the case.
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Check with a paper clip. Use a paper clip to “trick” the power supply into thinking that a connection has been established. Before proceeding, break the paperclip into a “U” shape.
- The paperclip will act as the pins that plug into the power supply and provide an on signal.
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Look for the 20/24 pin connector that normally plugs into your computer’s motherboard. This is usually the largest connector on the power supply.
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Find the green and black pins (pins 15 & 16). Proceed to plug one end of the paper clip into the green pin, the other end into the black pin. Before proceeding, you need to check that the power supply switch is turned off and that the power supply is completely disconnected from the power source and other components in the computer.
- The green pin is usually in the 15th position in the pin diagram.
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Insert the paper clip. After plugging the paper clip into pins 15 & 16, set this cable aside. Plug in the power supply and turn on the switch on the back.
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Check the blower. After the power supply is energized, you will hear or see the blower spinning. This shows at least that the power supply is still working. If the power supply doesn’t turn on, check the pins again (after unplugging) and try again. If still nothing happens, the power supply is most likely damaged. [1] X Research Source
- This method cannot test the normal operation of the power supply, but only shows that it is working. To know if the power supply has a stable output, you will need to proceed to the next method.
Check Output
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Check output through software. If the computer is operating normally and the operating system is bootable, try checking the output of the power supply with the software. SpeedFan is a free program that can read diagnostics and report back on your computer’s temperature and voltage. Please check the information to make sure everything is within acceptable range.
- If the computer does not work, proceed to the next step.
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Shutdown. Unplug and then turn off the switch located on the back of the power supply. Then, open the case and disconnect the power supply from all internal components. Trace each power supply cable to make sure everything is properly disconnected.
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Test the power supply with specialized equipment. You can buy a power supply tester at computer stores or online for a relatively inexpensive price. First, look for the 20/24-pin connector on the power supply. This is usually the largest size cable.
- Connect the power supply tester to the 20/24-pin connector.
- Plug in the power supply and turn on the switch. The power supply will automatically turn on and the light on the tester will light up.
- Some power supply testers need to be turned on via a switch or button. The rest will automatically turn on.
- Check voltage. The 20/24 pin connector has many outputs, but here are 4 important indicators that you need to watch:
- +3.3 VDC
- +5 VDC
- +12 VDC
- -12 VDC
- Check that the voltage readings are within acceptable tolerances. +3.3, +5, +12 have tolerances of +/- 5%. The index -12 can fluctuate in the range of +/- 10%. If any readings are out of this range, the power supply is unstable and needs to be replaced.
- Check other connectors. After determining that the main connector provides stable power, test each remaining connector. Remember to unplug and turn off the power supply between each test.
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Check the power supply with a multimeter (electrical measuring instrument). Straighten the paper clip into a “U” shape. Find the green pin on the 20/24 pin connector. Plug one end of the paper clip into the green pin (number 15), the other end into the black pin next to it. As such, the plug will receive a false signal that the cable is connected to the motherboard.
- Plug in the power supply and turn on the switch.
- Find the pinout of the power supply to determine which pins provide the voltage.
- Set the multimeter to VBDC mode. If the multimeter does not automatically adjust the range, you need to set it to 10V.
- Connect the negative terminal of the multimeter to the ground (black) pin on the .
- Connect the anode probe to the first pin to be tested. Remember to make a note of the voltage displayed.
- Check to make sure that the voltages of the pins are within tolerance. If any readings are out of tolerance, the power supply is faulty.
- Repeat this process with the other connectors of the power supply. You should refer to the specific pinout of each plug to know where the pins need to be checked.
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Reassemble the computer. After checking all the power connectors, you can reassemble the computer. Look in the notes to make sure the devices are properly connected and that all motherboard connectors are in place. Once assembled, turn on the machine.
- If the error persists or the computer won’t start, move on to the troubleshooting steps. At this point, the first part that you need to check is the motherboard.
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This article was co-written by Luigi Oppido. Luigi Oppido is the owner and operator of Pleasure Point Computers in Santa Cruz, CA. He has over 25 years of experience in general computer repair, data recovery, antivirus and upgrade.
This article has been viewed 5,010 times.
In the process of diagnosing problems on a computer, the power supply is often forgotten. However, testing the power supply first can save you a lot of trouble in troubleshooting. If your computer shows a blue screen of death (BSOD: Blue Screen of Death), a failing hard drive, or simply won’t boot, you probably have a power supply problem. Do the quick checks below before buying any expensive new hardware.
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