How to replace a desktop PC power supply unit (PSU)

**Larry ward** · 26-03-2009

Hello .. i need to change my power supply of cpu because there is no power going to your computer. I guess or may be sure that its the problem of power supply . could any one of you please let me know how to change the same ?

**Twitter** · 26-03-2009

Its a very difficult task. I recommend you to do the same if you are aware of what are going to do. Follow this steps carefully;-

Turn off your computer (if the PSU hasn’t failed completely, and it happens to be powered up) and unplug the power lead from the mains.
Remove the cover or access panel – this will depend on your computer case. With my PC, I was able to remove a side access panel, but you may need to remove screws and take off the whole cover. You might find it easier to work on your computer if it’s laying on its side.
The power supply is usually located at the top, back of the case. It’ll usually be secured by four or so screws. The mains power lead plugs into back of the power supply (the side that backs onto the rear of the computer case). On the front of the power supply (the side that faces the inside of the computer) you’ll see a number of cables leading to the motherboard and DVD drives, hard disks etc.

Gently pull out these leads from their sockets. You might need to use your thumb to release the catch that secures the connectors to the motherboard. Take note of which lead goes where. While it’s hard to plug connections into the wrong sockets, you’ll find it easier to put your computer back together if you note what goes where.

One colleague suggested taking a digital photo of where the cables go (while everything is still in place), while another uses sticky labels on both the sockets and cables to help him remember what went where. He puts one label on the socket from which he is removing a cable and marks it ‘A’, and then wraps a label around the cable he is removing and marks that ‘A’ as well. And another colleague suggested drawing a diagram of which lead goes where. Obvious, use whatever system will work best for you.
Now we need to remove the power supply. In my case this was down by removing the four screws that secured the power supply to the chassis of the computer, and then sliding it out of its position.
Take the new power supply, put it in place, and tighten the screws that keep it in place.
Attach the two motherboard cables to the motherboard. If you have an older computer, and you’ve bought an ATX 2 power supply, you may find that the main motherboard connector has four extra pins (see picture, above). You should be able to detach these extra pins so that the plug fits, or if this is not the case, hope that there is enough clearance to right of the socket on the motherboard to accommodate the extra pins.
Reattach the power leads for the hard disks and optical drives, and any other component that draws power.
Replace the cover.
Plug in the power lead to the back of the machine, and switch on your computer.

All going well, your PC should come to life. if it doesn’t, disconnect the power lead from the mains, and open up your computer. Check all the connections, especially the leads running to the motherboard, and try again.

**Kraker999** · 26-03-2009

Make sure you’ve got the right replacement power supply. These can be readily purchased from computer parts shops.To check what kind of power supply you need to get, look at the sticker on the existing power supply (you’ll need to open your computer to do this). In my case it read “A350w ATX P4 power supply” - this meant I needed an ATX power supply unit.

If there’s no sticker visible on the power supply, find out what kind of motherboard you’ve got, and use Google to find out what kind of power supply it works with.

Alternatively, remove the power supply from the machine (following the instructions below) and take it with you when you go to buy a replacement power supply.

Make sure that the new power supply has at least the same number of watts as the old power supply.