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You can start a compatible standard ATX power supply without a motherboard by briefly connecting its documented PS_ON pin to ground on the 20- or 24-pin main connector. Switch the PSU off and unplug AC before preparing the connection, and confirm the connector pinout and viewing orientation in the PSU documentation first. This is a basic startup check—not proof that the PSU can safely power a computer or deliver good-quality output.
Before you begin: confirm the PSU and connector are standard ATX
This procedure applies to a compatible desktop ATX PSU with a 20- or 24-pin main connector. Do not assume its pin positions match those described here if it is a proprietary, server, laptop, or otherwise non-standard supply. Check the model-specific PSU documentation for the pinout and any instructions about fan behavior.
In Intel’s ATX 3.0 design guide, PS_ON# is an active-low, TTL-compatible signal that lets the motherboard request that the PSU turn on. Connecting the documented signal contact to ground requests startup. A Supermicro 24-pin connector table identifies pin 16 as PS_ON and pin 17 as ground; those numbers are useful only when the PSU’s connector definition and viewing orientation match. Intel’s ATX 3.0 design guide and the Supermicro motherboard manual provide technical references.
How to start the PSU with a jumper
- Turn the PSU off and unplug its AC cord. Set its rear switch to off, then disconnect the AC cord from the PSU or outlet.
- Disconnect its DC leads from components. Remove the PSU’s connections to the motherboard, graphics card, drives, and other components before this isolated check. NZXT’s guide directs users to disconnect the unit from the system; follow the instructions for your model. NZXT’s PSU test instructions and Corsair’s PSU test instructions warn against bridging the wrong contacts, which can damage equipment or cause injury.
- Identify the correct contacts and orientation. Use the PSU documentation to find its
PS_ONand ground contacts. For the 24-pin view in Corsair’s illustrated instructions, hold the connector with the retention clip up and the pins facing you: the fourth contact from the left is pin 16 (PS_ON) and the fifth is pin 17 (ground). Do not count from a different view or rely on wire colors alone. - Bridge only those two contacts. A purpose-made ATX PSU jumper is convenient; a suitable paper clip or stiff wire is also described in the manufacturer instructions. Fit it so it connects only the documented signal and ground contacts, and avoid touching exposed metal while the PSU is powered.
- Restore AC and switch on. Reconnect the AC cord and set the PSU switch to on as directed by its manufacturer. Observe whether the unit responds. Follow the PSU manual for fan modes; some models have Zero RPM, Eco, or Quiet behavior that changes whether and how long the fan spins.
- Power down before removing the jumper. Switch the PSU off and unplug AC before taking out the jumper.
What the result tells you—and what it cannot
A fan that spins shows that the PSU received power and responded to the startup request. NZXT describes a fan response as a strong indicator that can help rule out the PSU as a failure point. It does not establish that the supply meets its rated output under load, has good voltage regulation or ripple, or that every protection circuit works correctly.
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A stationary fan does not automatically mean the PSU has failed. Zero RPM modes can keep a fan stopped, and Corsair notes that many of its units may spin only briefly when powered on. NZXT recommends disabling Zero RPM for its visual fan check. If the unit gives no response, check the outlet, AC cable, rear switch, jumper placement, and the model’s fan-mode instructions before drawing a conclusion.
When to use a PSU tester or multimeter
If you need electrical readings rather than a simple startup response, use a suitable PSU tester or multimeter only if you know how to use it safely and can follow the PSU manufacturer’s procedure. Corsair documents both approaches, while cautioning that tester readings for items such as -12 V and power-good timing can differ on newer ATX supplies. Consult current documentation for both the PSU and tester; a basic jumper test is not a substitute for those measurements.
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If the PSU still does not start
- Recheck that the AC outlet works, the cord is seated, and the PSU’s rear switch is on.
- With AC unplugged, verify that the jumper connects the documented
PS_ONand ground contacts—not neighboring pins—and that you counted them from the correct connector view. - Check whether a silent fan is expected under the PSU’s Zero RPM or other fan mode, using the manufacturer’s instructions.
- If there is still no response, stop rather than trying different pin combinations. Contact the PSU manufacturer or use an appropriate service or testing path.
These pin references and procedures concern standard ATX desktop supplies. For a different connector type or an uncertain pinout, use the exact model’s documentation instead of applying the 24-pin positions.
Quick Recap
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- The LCD power tester is a powerful power test device. This power tester only needs to be connected to the ATX connector of the power supply to easily and intuitively know whether the output of each power supply is normal. It can detect ATX, BTX, ITX, TFX computer power supply, and can display various voltage and PG values in liquid crystal to quickly detect the performance of computer power supply.
- The LCD displays various parameters such as output voltage and PG. When each parameter exceeds the normal value, the buzzer will sound a warning and the corresponding value will flash.
- It can measure the voltage of each group of power supply 3.3V/+5V/+12V/-12V/SB+5V/PG, and also measure the output wire P4/P6/P8/SATA/IDE, external DIE/SATA/P6/P8 is the light Displayed, there is no LCD voltage. Only the 24pin or 20pin will have the LCD voltage.
- It has LCD intuitive and accurate display voltage (+/-0.01V), automatic fault alarm, complete test interface, small and beautiful appearance, and many test functions. It is the best choice for quickly detecting PC power.
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- LCD DISPLAY: LCD liquid crystal display, the output voltage is clear at a . If there is any defect, the buzzer will automatically alarm.
- VOLTAGE DISPLAY: It can also measure the output wire P4/P6/P8/SATA/IDE, and the external DIE/SATA/P6/P8 is the light display, there is no LCD voltage. There is LCD voltage display only when connecting to the 24pin or 20pin.
- MINI and PRACTICAL: Now the number of power output groups is increasing. As long as one of them has problem, the hardware of the computer system may work abnormally or even burn out. To measure whether the output voltage output of the power supply is stable, the player usually uses a multimeter. But for the average user is still a little troublesome.
- ATX POWER SUPPLY TESTER: We have developed a portable computer power tester for the power supply market that cannot judge the quality of the power supply. It has LCD intuitive and accurate display voltage (+/-0.01V), automatic fault alarm, complete test interface, small and beautiful appearance, and more test functions. It is your best choice and helper to quickly detect PC power.
- WIDE APPLICATION: ATX Power Tester is a powerful power test device that can detect ATX, BTX, ITX, TFX computer power supplies, and can display various groups of voltage and PG values in the LCD screen, and quickly detect computer power supply to facilitate the instrument.
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