Complete Guide to Manually Check the Tower Desktops Power Supply Unit

Testing the Power Supply Unit is the first thing that we check when were troubleshooting a dead computer. I’m only saying this because, if you really having a dead computer on your side then there is 90% of chances that your PC’s Power Supply got faulty.

Not just the dead computer problem, because of a faulty PSU there are a lot more things can be happened to a computer; And it can be anything, like no display, or sudden shutdown/restart and etc.

To find it really is your PSU’s fault? The best thing what can you can do is to test its voltage output, just to confirm it’s working properly or not.

To check a PSU outside from a computer is actually an easy task to do and you really don’t need any technical or electrical knowledge too. And to perform all these testing steps, you’ll just need a screwdriver, PSU-tester and a paper clip, that’s it.

Note: The testing method what I showed in this tutorial to test a PSU will work on every type of SMPS either you have AT, ATX or eATX model.

#So, Lets See How to Test PSU;

Step 1 Cut the Power Supply: First you need to shut down your computer and then unplug it. You would also have to unplug all the peripherals device connected to the computer like keyboards, mouse, monitor & etc…

Step 2 Open the Computers Case: Next, you’ll need to lay down your computer’s tower towards right side to make the PSU accessible, after when you remove the side panel. For those who can loosen the screws a lot, then it is a good idea to use a Magnet screwdriver which comes in handy while you remove the side panel.

Step 3 Unplug PSU Connection: Now unplug all the connection coming from the PSU (SMPS) to all the internal hardware devices. Most of the connections contain clip attachment so make sure you lose the clip before removing any.

List of all the connections which you’ll need to remove:

  • 24/20 Pin ATX from Motherboard.
  • 4 Pin ATX from Processor.
  • SATA Power Connector from HDD/SSD & DVD-R/W.
  • 4/6/8 Pin ATX from Graphic Card (If Attached).

After when you completely unplug all the connections, then now it’s time to unscrews the PSU and put it outside the computer’s cabinet.

Step 4 Make a U-Shape Wire:  After when you completely unplug all the connections, now cut a piece of wire and turn it into a “U” shape (you can use a paper clip by bending it) and that will help you to short your PSU to test its working or not.

Step 5 Short & Test the PSU: Now find the 20 or 24 Pin ATX connector on your PSU (obviously the bigger one) and after that just locate the green and black wire on the connector. You can’t get confused because there is only one green wire available in that whole socket.

If your PSU’s Wire has a solid color, then you can try to put the notch downwards and starts to count the pin to 4th, from the right side.

After finding the green wire, then now it’s time to attach the power cord to the PSU and insert the metal wire into the green and black wire (right next one) socket. This will short the PSUs Circuit which can turn it ON, outside the CPU.

So now, if your PSU fan still doesn’t move or maybe move just for just a sec and then stops, then it means that you have a faulty SMPS by your side and your PSU needs replacement.

If your PSUs Fan is running perfectly without any of lags and stoppage, then it means that your PSU is working fine. But sometimes it’s also possible that the fan works properly but the actual problem is coming from a particular circuit section of your PSU which leads to the power supply related issues. In this condition, just move to the next sub-topic to troubleshoot the PSU by using an advance check-up.

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#Advance Testing

A power supply tester is very handy and is used by most of the computer technicians. The power supply tester is an easy way of finding out if there is a problem with the PSU. It helps you check if the PSU conforms to the current ATX specifications.

Safety Precautions: Before we begin discussing how to use the power supply tester, we suggest you take the following precautions:

  • Make sure that the power switch is off and remove the plug for extra precaution.
  • Remove all accessories on your hands.
  • Be vigilant and check for smoke or a burning smell.

Step 1: Make sure that you move to a working area where you have adequate space for the PSU along with all the wires.

Step 2: Plug the ATX 24-pin Motherboard Power Connector and the 4 pin Motherboard Power Connector.

Some PSUs may use a 6-pin or an 8-pin connector instead of the 4-pin connector. Depending on what you have, you may have to connect one of those. Make sure that you use only one connector along with the 24-pin connector at a time.

Step 3: Switch on the Power on the Power Supply Unit and Switch on the tester. The LCD screen of the tester will light up and it will show details related to the power voltages that the PSU can deliver. You may see the following:

  • +3.3 V
  • +5 V
  • +12 V
  • -12 V
  • PG

If any of the voltage is flashing because it is outside the range or if the voltage shows “LL or “HH” then your power supply is not functioning properly. The PG value should be in-between 100 to 500ms. If it is not within this range then it will flash to inform you that there is a problem. This means that there is a problem with the PSU.

If you power supply unit tester indicates that all voltages are correct then you can proceed to test the peripheral power connectors one at a time.

Step 4: Check Peripheral Power Connectors – The PSU tester may not be able to distinguish the different connectors if you connect all at the same time. So, remember to use one connector at a time to check the power supply for peripheral devices. The two motherboard power connectors should be connected at all times when you check for power supply for the peripherals.

The lights on the tester next to the LCD screen will light up when you connect the peripheral device power connectors. Each connector will light up the corresponding lights. The SATA cable should light up all the three lights:

  • +12V
  • +3.3V
  • +5V

The 4 pin Molex and 4 pin Floppy Drive power connector should light up the +12V and +5V lights.

If any of the corresponding lights do not light up appropriately then there is a problem with the power supply. If things work fine then you know that your PSU is good and you can return it to the computer.

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“And that’s all for now, thanks for sticking with the article, and you know it will always good to let me know about the tutorial, in the comments down below.” 🙂


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    you simply shared this useful information with us. Please keep us
    up to date like this. Thanks for sharing.


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