Would you like to avoid the cost of buying a new PC because your computer power supply is dying, and instead extend the life of your current computer?

This post provides you with guidance steps and pictures on how to replace a computer power supply, after the PC power supply unit (PSU) failed. Here at School for Engineering, we are big fans of repairing and replacing parts where possible (here a new power supply unit), and we want to be able to help you get more life out of your current computer.

First, the very boring disclaimer:

And first, the very boring disclaimer. We do not accept any responsibility for any injury or damage to anyone or their property as a result of following these instructions; you are replacing your PC power supply at your own risk.

Always consult any manual you receive with your new power supply for instructions for safely removing or reinstalling the power supply unit, and do not proceed unless you are comfortable with attempting this removal and installation yourself.

Do you suspect your computer power supply is failing?

We have listed some indications here that your computer power supply unit may be failing. This list isn’t exhaustive, and there are better sites out there which help you diagnose whether your PC power supply unit is faulty, for example here. Our tutorial’s focus is to show you how the computer power supply can be replaced once you a reasonably sure it’s the problem.

Symptom type #1: PC is intermittently crashing or freezing

For some weeks before PC power supply failure, your computer might be behaving oddly; for example it crashes randomly or freezes at strange times. Additionally there may be more noise than usual coming from the PC case. If you see intermittent events like this, make extra sure that you are backing your PC up regularly, even if you aren’t changing your power supply unit.

Symptom type #2: PC failing to turn on at all

Your PC may not turn on at all. If you have eliminated the obvious causes for this: power cord not plugged in at the back of the PC or at the wall socket, or the wall switch or PSU switch is off, then it is possible that your PSU has completely failed.

Here’s how to replace a PC power supply when it is faulty

Having decided that you need to replace a PC power supply, here are the steps (with tips) on how to remove the existing PC power supply unit, and then install a new computer power supply.

Step 1: Unplug the PC from the mains electricity supply and switch it off

Make sure that the power cord to the PC is disconnected and the switch to the power supply unit (PSU) is turned off – you need to make absolutely sure that there is no electricity supply to your PC while you are fiddling around inside the computer case.

Step 2. Remove the two long sides of the PC case to get access to the PC power supply

To help with the removal of the power supply unit, take both long sides off the PC case. The screws for the sides of the PC are often designed to be unscrewed by hand. Remove these screws and put these to one side in a safe place. Here is one of the long sides of my PC case; note that the power supply unit is attached to the case at the top (shown in the top left of the photo):

The other side of the PC with the side removed is shown in Figure 2.

From Figure 2, it will be noted that the existing cables are routed from the top right of the photo (the PSU), down across the outside of the case and into the square gap at the bottom left of the photo. The cables have also been fastened together with cable ties in a number of places. This is in order to keep the power cables tidy and avoid them making contact with the internal PC components as much as possible.

Standard Power Supply Connections Available from a PSU

HDD = hard drive, SSD = solid state drive (storage), ODD = Optical Disc Drive or Optical Digital Disc

Step 3. Check your existing PC power supply model (and buy a PSU replacement)

Having removed the sides from the PC, I can at this point see that my existing (and now very dead) power supply, to be removed in my PC, is the Aerocool Integrator 500W. At the time of writing, this power supply model is still readily available, but if yours isn’t, it is worth finding a similarly specified power supply.

If this PSU were not available, I would try to find another similarly specified power supply unit, with the same range of connectors. You will know what connectors you need when you remove your existing computer power supply (and take a note of these connectors as you disassemble).

Depending on what power supply unit you need to replace, you can find great options for new PC power supply units at Ebay (US)*, Ebay (Canada)*

At this point, the existing PSU is still fully attached, via screws into the PC casing, and each power cable from the PSU is connected to each PC component which requires power.

Note that the following Step 4 (unscrewing the existing power supply from the casing) and Step 5 (removing the PSU connections) are interchangeable. You have the option of:-

• unscrewing the PSU (Step 4) before detaching the PSU from the other PC components it supplies power to (Step 5), or
• you can remove the existing power supply connections first (Step 5) whilst keeping the PSU attached to the case. I carried out Step 4 first.

Step 4. Unscrew the existing power supply from the casing

There are four screws attaching the power supply to the case, and also (in this particular instance) a small ledge in the corner of the case which the power supply can rest on to help keep it in place. 

When you unscrew the screws, bear in mind that you may not get another set of screws with the new power supply (depending on which one you buy) so it is a good idea to keep your existing screws safe.

Once the power supply has been removed, your PC will look something like in Figure 6:

Step 5.   Remove the existing Power Supply Unit Connections with PC Components one at a time

The existing power supply unit (PSU) will have a number of different connections to the PC components, all of which will have to be disconnected.  When a new power supply is installed, these connections will have to be reconnected in the same manner as before, so to help out here’s tip #1: 

Tip #1!  – note each connector and its location in the PC as you remove it

As you remove each connection from the old power supply, note each PC part you are removing a power connection from, and its position in the PC casing.  This is so you can find that connection point again for every part of the PC which requires a power supply connection. 

For example, you could take a note of existing connection by putting a bit of brightly coloured electrician’s tape on the spot where you have just removed a connector from, or taking a photograph of each relevant connector and the immediate area around it inside your PC casing. 

In my particular PC’s set up (yours may differ), I had the following connectors from the PSU to remove:

Step 5a): Remove 20+4 Connector from the motherboard

The 20+4 connector powers the motherboard on this PC, as shown in Figure 7:

Step 5b): Remove ATX 12V 8-pin connector from the motherboard

The ATX 12V 8 pin connector from the PSU should be removed from the motherboard; shown below is the connection point on the PC motherboard where the ATX 12V 8-pin connects:

The ATX 12V connector which also powers the motherboard, has a pin profile shown in Figure 10:

Step 5c): Remove a SATA connector from the HDD

Next, remove the power connection from the hard disc drive (HDD) – this is a SATA style connector pin (shown in Figure 11 below):

The SATA connector is connected to the hard disc drive in the slot shown in Figure 12:

Another view of the hard disk drive shows the hard disc drive with an unfilled SATA connector slot on the left, and an unfilled FDD slot on the right is shown in Figure 13. The SATA slot is empty as SATA cable has been removed but the FDD slot remains empty as it is not used at all:

Step 5d): Remove a SATA connector from the ODD

The optical disc drive (ODD) also has a SATA connection from the power supply unit (Figure 14). When you replace a PC power supply, the SATA connection for things like an ODD must also be removed and subsequently replaced.

Step 5e): Remove the PATA Molex 4-pin connector from the PC Fan

The PATA Molex 4 pin connector is used to supply power to the PC fan in this particular PC setup.  The connection from the PSU to the PC fan is comprised of a female PATA connector (which comes from the power supply unit and is black in colour) and a male PATA connector (which is coloured white) which goes to the PC case fan. This is illustrated in Figures 16 and 17

The PATA Molex 4 pin which comes from the PSU looks like Figure 18:

Step 5f): Remove the APCIe 6-pin connector from the GPU

As was seen in the tutorial post here on how to install an Nvidia GPU which enables you to train a deep learning model faster, if you have a GPU, it often requires its own dedicated power supply. 

For this PC set up configuration, the plug powering the GPU is a APCIe 6-pin connector and is shown in Figure 19:

When you replace the PC power supply , the PCIe 6-pin connector for the existing is removed from the GPU as shown in Figure 20:

Step 6: Install a new Computer Power Supply

Step 6a): Screw the new PSU into the PC casing

Just as you unscrewed the old power supply unit, installation of the new PC power supply unit should be carried out by laying the PC flat on its side (or upside down) and slotting the PSU into the top corner of the case, and screwing the screws in to fix it into place.

Step 6b): Re-attach each individual connector to the relevant component when you install a new PC power supply

The old power supply unit connectors removed one by one from your PC components, set out in step 5(a) to step 5(f) should now be connected with the new power supply unit in the same way as they were initially removed in order to install a new PC power supply. For example the figures below (Figures 21 – 23) show examples of the new connections made again when you install a PC power supply:

In the course of reconnecting the PC power supply unit cables, bear in mind Tip #2:

Tip #2: Route as much cabling as possible around the PC casing

In Step 2, there was a photo showing the existing power supply unit’s cabling set up before the connections and the PSU itself is removed from the PC case. Note that in that picture, the cables have been routed between the outside of the casing and the side of the PC (removed), in order to keep the cables away from the internal components as effectively as possible.

When you are installing the new PC power supply unit and connecting up each new PSU connector to the existing PC components, where possible, route the cabling along the outside of the PC casing and back in, in the same manner shown in Step 2.

Step 7: Try the new Power Supply Unit

You may wish to try the new power supply unit once all the power connections have been reconnected, but before you have tided up the PC cabling and reattached the PC sides. In doing so, ensure that you do not touch anything live in the PC, but instead plug the PSU plug in at the back of case and plug in at the mains. Switch the PSU on using the PSU switch on the back of the case, and switch the computer at the on switch at the front, to check whether the PC boots up. Everything inside the PC is potentially live, so do not touch anything inside the computer.

If you are feeling confident following this that the PSU is now working, plug in a monitor to see what the booted up PC is doing. Turn off the PC again, before continuing to tidy the cables and put the sides back on. Once the PC is off and you are tidying up the cables, be sure to follow Tip #3:

Tip #3: Use cable ties to tidy the new cables inside the PC casing 

When you are finished routing all the cables into their new connections, use new cable ties to tidy up the newly routed cables and secure them together on the outside of the PC case.

Step 8: Re-attach the PC sides

Re-attach the long PC sides by slotting them back on and screwing them in place – you should still have the PC case screws from Step 2.

Conclusion

This tutorial has illustrated how you can replace a PC power supply unit when it has failed or is in the process of failing. If you liked this tutorial on how to install a new computer power supply, you may also find the tutorial here useful – it covers installing a GPU optimized for faster deep learning on your PC.

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