Skip to main content

When a PC suddenly goes on the fritz for no apparent reason, checking the PC power supply first may save a lot of time troubleshooting the system. A faulty PC power supply belies many intermittent computer problems. This is why experienced PC technicians often look first at the PSU when diagnosing PC hardware issues.

  • System failures during the boot-up process.
  • The PC doesn’t power on at all
  • Spontaneous restarts or lockouts when trying to use the machine
  • Case fans and hard drives that do not spin
  • An overheating system due to heatsink and fan failure
  • Errors related to system memory
  • Recurring Blue Screen of Death (BSOD)

If the PC does not turn on at all

As with any troubleshooting situation, disconnect all but the necessary peripherals from the PC. Usually this means you’re left only with the mouse, keyboard and monitor connected.

Many power supplies have an external switch located at the rear of the unit. Check that it has not been accidentally been switched off. Plug the PSU power cable into a wall socket or surge protector, and turn on the computer. Most power supply models have a light on back of the unit that glows when it’s powered on. If it doesn’t light, try a different power cable and a different socket to eliminate those items as the source of the problem.

Normally you can observe a few things that indicate proper operation of the PSU.

  • Listen for case fans, and mechanical hard drives. You should hear these devices spinning.
  • Check the connection for each PSU cable running to the computer hardware component.
  • Look inside the case for the motherboard light. Usually flashing lights on a motherboard indicate a faulty or misconnected power supply.

As an aside, the color of the motherboard light can tip off other malfunctioning components. Lights and BIOS beep codes vary by manufacturer. Check your motherboard product manual for that information.

Using a paper clip to test a power supply

The paper clip test, alternatively called the jumper test, allows you to verify PSU functionality when it is disconnected from the components inside a PC. This test will identify some common issues:

  • Short circuits inside the power supply
  • Failed components
  • A live power connection

First you want to turn the power switch at the rear of the power supply to the off position. (O should be ‘down’)

Locate the 20+4P (24-pin) connector. Bend the paperclip and insert one end into the green pin (PS_ON) and the other into any of the black pins (Ground).

Flip the switch at the rear of the PSU, and listen for the internal fan. If you can hear the fan, this should verify the power supply is turned on.

The paper clip test is a crude but effective way to confirm if your PSU needs to be replaced. It will not tell you much else. If your power supply passes the paper clip test, you still may need to identify related issues:

  • Voltage fluctuations
  • Overheating
  • Power rail failure

Should you get out the multimeter?

To perform more nuanced testing of your power supply, you will need to use or buy a multimeter. A multimeter is an instrument that measures electrical current, principally voltage (volts), current (amps), and resistance (ohms). If you’re an electronics technician, you probably have one already, and are definitely familiar with this tool.

If you’re working as an internal IT, it probably isn’t worth your time to get overly intensive with power supply testing and repair. The cost of a new PSU is relatively low, and does not justify extensive personnel hours dedicated to a complex diagnosis. It is common practice for departments that manage multiple PCs is to keep spare power supply or two on hand for “swap” testing to identify when a PSU is the root cause of recurring computer problems.

If your computers are under warranty and you suspect the power supply may be to blame, that’s when you would take advantage of manufacturer support and warranty for desktop computers that you purchase. If you’re buying your business computers as finished systems, it’s a better use of company resources for the manufacturer to troubleshoot faulty computer power supplies and other components, while your team gets to work on a freshly replaced PC.

Adam Lovinus

Author Adam Lovinus

A tech writer and Raspberry Pi enthusiast from Orange County, California.

More posts by Adam Lovinus

Join the discussion 4 Comments

  • Ernest W. Buller says:

    I have a PSU tester, but all power supplies show a fault, regardless of actual condition. It sure would be nice to have one that gives accurate results. (I have attempted to contact the manufacturer whose PSUs I use exclusively – Antec – but I have not received any response from them.)

  • JAACK says:

    If the paper clip trick doesn’t work, WHAT’S NEXT??? Have 4 bad supplies 3 – 600 watt and 1 1000watt EVGA supplies. Did see anything obviously wrong. There were no burned or broken components. There were no swollen, leaking nor otherwise bad electrolytic capacitors. The PC boards are intact i.e. broken traces. It is Very difficult to troubleshoot without schematics aka wiring diagram. I don’t want to make these things land fill donations!!! From my limited PCB circuit tracing looks like it could be shorted bridge rectifier &/or filter caps before the fly back circuits and No +5 volt standby. What’s next???

  • shakil says:

    Like!! Really appreciate you sharing this blog post. Really thank you! Keep writing.

  • TheGreenLungo says:

    I can boot and mine ETH no problem, but games like Cyberpunk2077 crash to blue screen on load or shortly after. Under high load, Hardware Monitor shows 12V rail voltage sagging down as low as 11.6V. My voltmeter set to DC mode shows 11.9V in the same conditions when I measure at the cable leading to the video card. When set to AC mode, I read AC voltage pulses in excess of 20V then ramps down to zero before repeating this ever 2 seconds or so. I can’t be certain at this point, but if anyone else is experiencing something like this, I think we have to accept the possibility that the voltage regulators in the PSU are failing to keep up with the demand for current and throwing unstable DC voltages with intense ripple. That means at the peak of the wave, the voltage is double the target 12 volts, then dropping to zero. No wonder system is giving up. Hardware monitor shows you the DC voltage measured as an average value, but does not show the AC hum that blurs the voltage.

What's your take?