Boot your PSU without a Motherboard


Please note: Follow this guide at your own risk.


Often in power supply tests at Tech- Reviews, we sometimes need to power up power supplies without a PC e.g. When recording voltages of units without any devices attached. Furthermore, many water cooling enthusiasts also need to do this when carrying out leak tests. You maybe thinking that this is very difficult, but fortunately, it’s simple procedure which I’ll explain below.


The connector we’ll be using for the guide is the 20 /24-pin ATX connector. On this connector there is an assortment of different coloured cables which provide different voltages to different parts of your motherboard. One important cable attached to this connector is the black wire, otherwise known as ground.

The ground wire is like the name suggests, it’s a connection between your PC and the ground. This wire helps in discharging static electricity so you can work safely inside your computer without causing any damage to any of the components. You can read more about the ground wire here.

Another important cable (which we’ll be using for this guide) is the green wire. There is only one green wire on the PSU and it’s found on the ATX connector. So what’s the green wire? In simple terms, the green wire is ‘Power On’. So when you switch on your PC at the front, the circuit to the green wire is completed, hence, switching on your computer.

Therefore, one way to power on your PSU would be to create a closed circuit with the ‘Power On’ cable. We can do this very easily with one single cable.

The Stages

  • First off, turn the switch on your power supply to ‘off’
  • Cut a cable – three inches long – off of an old power supply or spare modular cable – making sure it’s the same thickness as the cables on your ATX connector
  • Strip the ends of the wires for easier connectivity
  • Bend the cable slightly in the middle
  • Now this is the main bit, connect the green cable’s terminal in the ATX connector with one of the black cables’ terminals in the ATX connector. It doesn’t matter which black cable you use, as all of them are ground, just make sure you have connected the green wire
  • Providing you’ve done everything correctly, just hit the switch and your PSU should start within a couple of seconds
  • If the power supply doesn’t turn on, there’s likely to be a problem with the PSU or that you’ve connected it to a wrong cable. If this is the case, your best bet would be to remove the wire and turn off the unit immediately.
Switch on your PSU without a Computer
Click to enlarge

The Voltages

If you check the voltages of the power supply at this state (without anything attached), you should notice that the unit isn’t as stable. Reasoning for this is because as more power is drawled from the PSU, it often becomes more stable.