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Replacing a Computer Power Supply Unit

Easy step by step instructions showing you how to replace your own PC computer PSU, or power supply unit, presented by Crafty Corner

For any questions contact us via email

replacing pc psu power supply

What you need:

  • Star screwdriver
  • Replacement PSU (power supply unit)
  • Cable ties

It's going to happen sooner or later, after a storm or power failure you switch your PC on, and nothing happens... your computer stays off! This is usually because the power supply unit (PSU) within the computer has been damaged.

In my experience as a computer technician, I have found that damage through a power surge very rarely goes beyond the power supply. This easy, step by step project will show you how to remove and replace the power supply inside your PC so that you can avoid the expense of a computer repairs workshop.

If you are new to working on computers, it is a good idea to read through all the steps first to familiarise yourself and make sure you know what you are doing. Don't panic! As long as you work slowly and pay attention to each step, replacing your PSU should be relatively easy and hassle free.

Step 1

Unplug your PC, and then unplug all the cables that come out the back of your computer. If you are nervous about doing this, you can make a diagram or label all the cables to make sure you return them to the right place.

Place the case on a desk and turn it so that you can see the back of the computer where all the cables plug into.

front of pc computer back of pc computer

Step 2

Locate the screws on the right that hold the side panel in place. Often these will be screws that look like they can be opened with a small spanner, or they can be thumb screws.

The latter are easy to identify as they tend to stick out of the back of the PC and have a grip on them so that you can use your fingers on them. In this case we have standard screws which we will remove with a star screwdriver.

computer thumb screw computer standard screw

Step 3

Now lie the PC on its side and slip the panel towards the back and then lift it off, exposing the insides of your computer.

pc computer on side lift computer side panel internals pc computer

Step 4

Now we need to remove all the power cables. We recommend that you draw a small diagram of the insides of the computer showing where all the cables go, or to use little stickers so you can label the cables before you remove each one.

Because each plug on a computer has a different shape, you cannot accidentally plug the wrong plug back in later, so do not be too scared. First you identify your PCU, optical drive (CD or DVD drive), and then your hard drive. It will be hard to see the cable that leads to the motherboard until these are out the way.

psu computer power supply harddrive computer cables motherboard cables

Step 5

Most PC technicians and computer shops have anti static cables that they use to prevent static damage to the computer. As a home user, make sure you are standing on the floor with rubber soled shoes, and hold the side of the case to "short" out your body safely.

We recommend you do this each time you bring your hands near the computer before touching anything inside. If you have a friend or family member who does not mind being shocked, you can touch them first before the PC to get rid of the static charge.

computer static charge

Step 6

Then, starting at the hard disk drive or the bottom, remove the SATA data cable (picture on left) and then the power cable (picture on right). Gently pull the data cable off by the connector right against the hard drive (try not to pull the cable itself).

hard drive data cable hard drive power cable

Step 7

Repeat step 6 with your optical (CD / DVD) drive, first removing the date cable (picture on left), and then the power cable (pictured on right).

dvd data cable dvd power cables

Step 8

Once you have pulled the cables to one side, you will see there is a power cable attached to the mother board. It is easy to identify as it has about 24 cables attached to it. If you look closely you will see that there is a clip that holds it in place.

Using your index finger press the top of the clip and pull the jack off the mother board. Sometimes you will see you have a 4 pin jack left behind, simply remove this in the same manner.

pc motherboard cable press clip on motherboard cable

Step 9

Finally, remove the additional 4 pin plug that you see connected near your processor fan. Note that this jack also has a clip that you need to press and remove as with the main power cable.

4 pin power cable

Step 10

Now move all the power cables and hang them outside of the computer box to ensure that you have removed everything and the PSU is free to be removed.

If you find you still have power cables attached to devices in your computer, especially if you have a second hard disk drive (HDD) or auxiliary power to a graphics card, remove these too, making note of the cables that were attached.

remove pc computer cables

Step 11

Now turn the computer case so that the back is facing you and you are looking at the point where you would insert the power cable from your wall plug.

You will see that there is a fan, and near the fan are two "case" screws. Evenly spaced away you will see two other screws, a total of 4 screws hold all standard PSUs inside the computer. Using your star or Phillips screwdriver, remove all the screws.

computer power supply screws remove computer psu screws

Step 12

Now that the PSU is loose, slide it forward and tilt it away from the top of the computer so that you can slide it out the machine.

slide psu power supply unit forward tilt pc psu computer power supply unit

Step 13

Now that you have removed the power supply you can take it with you to your local computer shop and ask them for a replacement one. This should normally only cost about R180.00 R300.00 depending on the size or strength of the power supply.

Before you purchase your new power supply, ensure that you have the correct plugs that match the ones on your old power supply. Also check that you have enough SATA power points, if not get as many adapters as you would need, and if you are unsure, ask the store assistant.

motherboard molex plug computer auxillary power plug computer stat power plug pc computer power adaptor plug

Step 14

Now insert your new PSU or one you have taken from another computer, as in this case, and position it so that you can see the 4 screw holes. Holding the power supply in position, screw at least two screws in with your fingers to hold it in place. Remember to earth your hands on the case before working inside the computer.

position pc computer power supply insert computer psu screw tighten psu computer screw with fingers

Step 15

Using your Phillips screwdriver tighten the power supply unit into place, making sure not too over-tighten the screw as the cases are only made of thin tin.

tighten pc computer psu screws

Step 16

Finally you can start re-attaching the power cables. Starting with the motherboard, insert the cable.

Note that the plug can only fit one way, if you look closely at your plug you will see one side has a few square pins and the clip on the one side, match these square pins and the lip orientation so that it is the same as the mother board. Then insert the aux power to the mother board, the 4 pin plug.

computer motherboard power computer auxillary power plug

Step 17

Now fit the power cables to your optical drive, the hard drive and any additional cables you found when you first removed the power supply. Remember to always install the power cable first and then the data cable.

fit computer power cables attach pc computer sata cable

Step 18

Before you test your computer, ensure that you tie up all loose cables so that nothing is obstructing any of the cooling fans inside the computer. This is VERY important as you can damage your CPU by overheating it if the fan is jammed by a power cable. Tie up the cables with a cable twist or a standard cable tie.

computer cable ties computer cables free psu

Step 19

Before you close up the PC tower, plug it into the mains from the wall and press the power button. If, as we predicted, it was only a power supply that was faulty the fans should now turn on and you should hear the computer beep.

In the event that nothing happens, the damage could be more extensive or you have not plugged in all the cables. Check that all the cables are properly plugged in and try again.

restore pc computer power test pc computer power

Step 20

If all is working, restore the side panel and then restore your computer to your desk or its normal place. Insert all cables and turn on. If all goes well the computer will now function as it did before the burn out.

Step 21

In the event that nothing happens and you have rechecked that all your cables are plugged in correctly, you may have a more serious problem. In this case, take the PC to your local computer shop for more extensive testing.