When a PC will not power on, the first question is whether the power supply is even alive. The paperclip test, more properly called a jumper test, forces the PSU to turn on outside the system so you can confirm the fan spins and voltages appear. It is a five-minute check that separates a dead PSU from a dead motherboard, and it needs nothing more than a paperclip and, ideally, a cheap multimeter.
What the test proves and what it does not
A passing paperclip test tells you the PSU powers on and its fan runs. It does not confirm the unit delivers clean, stable voltage under load, because there is almost no load during the test. Treat it as a quick “is it dead?” screen, not a full health certificate. A unit that spins its fan here can still fail the moment a graphics card demands real current.
Safety first
- Unplug the PSU and disconnect it from all components before starting.
- Never open the PSU casing; capacitors can hold a charge.
- Work on a non-conductive surface and keep the unit away from liquids.
Step by step
- Disconnect the 24-pin cable from the motherboard and everything else from the PSU.
- Straighten a metal paperclip into a U shape, or use a dedicated jumper.
- On the 24-pin connector, find the single green wire (PS_ON) and any black wire (ground).
- Insert one end of the clip into the green pin and the other into an adjacent black pin.
- Plug the PSU into the wall and flip its switch on.
- The fan should spin. If it does, the basic power-on circuit works.
Pin reference
| Wire color | Rail | Role in test |
|---|---|---|
| Green | PS_ON# | Jump to ground to start |
| Black | Ground | Return path |
| Yellow | +12 V | Measure with multimeter |
| Red | +5 V | Measure with multimeter |
| Orange | +3.3 V | Measure with multimeter |
Going further with a multimeter
A spinning fan is a good sign, but to check voltages, set a multimeter to DC volts and probe a yellow-to-black pair, then red-to-black. Healthy readings sit within about 5% of nominal: 12 V rails should read roughly 11.4–12.6 V, 5 V rails 4.75–5.25 V, and 3.3 V rails 3.14–3.47 V. Readings far outside those windows point to a failing unit even if the fan spins. Note that these are no-load figures; the real test of stability is how the rails behave with a full system drawing power.
Why some fans do not spin during the test
Many modern power supplies include a semi-passive or “zero RPM” mode, where the fan stays off until the unit gets warm or loaded. On such a PSU, a still fan during a no-load jumper test is not proof of failure. Feel for a faint hum, or better, rely on multimeter readings rather than the fan alone. This is one more reason the paperclip test is a screen, not a verdict, and why a multimeter turns it from a guess into a measurement.
When the fan does not spin
If nothing happens and the unit is not a zero-RPM design, double-check the wall outlet and the PSU’s own switch, then confirm you jumped the correct pins. A modern PSU that still refuses to start after a correct jumper is almost certainly the fault, and if it is under warranty, this test is enough evidence to request a replacement.
FAQ
Will the paperclip test damage my power supply?
No, when done correctly. You are simply doing what the motherboard does when you press the power button. The risk comes from touching the wrong pins or shorting across the connector, so seat the clip carefully in the green and a black pin only.
Can a PSU pass this test and still be bad?
Yes. The test runs with almost no load, so a unit with weak capacitors can spin its fan yet collapse under a gaming load. Use the paperclip test to rule a PSU dead, and swap-testing with a known-good unit to confirm one that behaves oddly under load.
Bottom line
The paperclip test is the fastest way to answer “is my power supply completely dead?” Jump the green pin to a black pin, power on, and watch the fan or, better, measure the 12 V, 5 V, and 3.3 V rails within about 5%. Remember zero-RPM designs may keep the fan off, and that no-load results cannot certify stability. It is a screening tool, not a stress test, but it turns a mysterious no-boot into a clear next step.
