How To Replace Your Power Supply
By Gabriel Torres on August 8, 2006
O.k, so you are a complete layperson, has never open your computer case, is afraid of doing so, but want to replace your power supply unit with a better one. This tutorial was just made for you: a step-by-step guide on how to replace your power supply full of pictures, especially made for people who has never opened the PC case and/or is afraid of changing things inside the PC.
Why should you replace your power supply? If you don’t specify a power supply brand and model when buying your computer, the computer store will probably sell you a PC with a “generic” power supply, which is very low-end and isn’t enough for high-end applications. Telling them the power rating you want is not enough, since cheap power supplies simply cannot deliver their labeled power rating. For example, a 400 W “generic” power supply won’t be able to deliver its rated 400 W.
Your computer may be working just fine with a cheap “generic” power supply, however when you upgrade a computer part of your computer – specially the video card – you may face stability issues if your power supply can’t deliver enough power to your system. By “stability issues” we mean your computer reseting out of nowhere, the infamous Blue Screen of Death and your computer “freezing”. Also, if your current power supply is overheating – i.e., if you place your hand on top of your computer right above where the power supply is installed and it is very hot – it is time to replace it with a better power supply.
Luckily there are several terrific power supply manufacturers nowadays on the market. Buying a new power supply (or PSU for Power Supply Unit, as it is often called) has no mystery. Select your new power rating and buy one. Any power supply unit should fit your computer nicely, but just in case you should buy an ATX12V 2.x power supply. If your motherboard needs an EPS12V connector – which is very unlikely – you will need to buy a power supply that offers an EPS12V connector. We don’t think this is your case, as only a few very high-end motherboards requires this connector, and if your motherboard does, you are probably already using a high-end power supply anyway.
Power supplies up to 500 W will do the job for the majority of users. Above that only if you have several hard disk drives and/or are using two video cards under SLI or CrossFire modes. For an overall view on power supplies including their main specs, read our Power Supply Tutorial. This tutorial may be handy when buying a new unit.
So let’s roll up our sleeves and work! The first you should do is to disconnect all your computer external cables – especially the power cable – and put it on a table. Put the rear part of the computer facing you. Pay attention on the screws located there. You will play with six screws, two located on the right-hand side that fasten the case side panel (i.e., the case “door”) and four that fasten the power supply unit to the case, see Figures 1 and 2.
You will need a Phillips screwdriver. Remove the two screws located on the right-hand side that fasten the case side panel and slide this panel as shown in Figure 3.
In Figure 4 you case our case opened and the exact location of our power supply.
Before removing the power supply, you need to disconnect all power connectors that are installed on different devices inside the computer.
Remove all power connectors that are installed on different devices inside your computer. In our case our computer had a CD burner, a hard disk drive and a floppy disk drive, so we had to remove the power connector from these three devices, plus the motherboard. Depending on your configuration you will need to remove more cables.
As for the motherboard, usually two connectors are used: a main connector with 20 or 24 pins and an auxiliary 4-pin connector, called ATX12V. Some low-end motherboards don’t have this ATX12V connector. You need to look for it carefully as usually it isn’t located near the main power connector – even though on our motherboard they were located side-by-side, this setup isn’t the usual one.
Remove the motherboard power connectors is a two-step procedure, first press the latch located on the middle of the connector and then pull the connector up. In Figure 9 we illustrate the removal of the main motherboard connector and in Figure 10 the removal of the ATX12V auxiliary connector.
Now that all power cables are disconnected, it is time for you to remove your old power supply, by removing the four screws that fasten it to the case. You will need to hold the power supply with one of your hands while removing the last two screws, as shown in Figure 12.
After removing the four screws, slide your old power supply to the front of your computer case, as shown in Figure 13. After that, you will be able to remove your old power supply from your computer.
Installing your new power supply is the inverse process we’ve done to remove your old unit.
First place the power supply in its place, sliding it to the back of the computer case, as shown on Figures 16 and 17.
Next, screw it to the case. You will need to hold it with one of your hands.
The next step is to connect all power cables to all devices inside our computer.
Now you need to connect all devices to the power supply. In our case our computer had a CD burner, a hard disk drive and a floppy disk drive, so we had to connect these devices to the power supply, plus the motherboard. Depending on your configuration you will need to install more cables.
Notice that all power connectors have a correct way to be inserted, i.e., they have a “right” and a “wrong” side. If you can’t insert a power plug, just flip it and try it again, as it may be at the wrong position.
Now it is time to connect your power supply to your motherboard. As you know by now, two connectors are used: a main connector with 20 or 24 pins and an auxiliary 4-pin connector, called ATX12V. Some low-end motherboards don’t have this ATX12V connector.
Let’s first install the smaller connector (ATX12V), as shown in Figure 23.
Power supplies following ATX12V 2.x standard – i.e., the power supplies you will find on the market today – use a 24-pin connector. So if your motherboard uses the ATX12V 1.x standard – i.e., it uses a 20-pin power connector – you will need to transform the main power connector from your power supply from 24-pin to 20-pin. This can be done through the use of an adapter that comes with the power supply or by removing the four extra pins, which was the case of our power supply.
Since our motherboard was an old one using a 20-pin connector, we needed to transform the power supply 24-pin connector into a 20-pin one, as shown in Figure 24. The mechanism used on your power supply may be different.
Of course if your motherboard uses a 24-pin connector you don’t need to do this.
Now connect the main power supply connector to the motherboard, as shown in Figure 26.
Your new power supply is now completely installed, however you may have notice that several power cables are left over. Unless your power supply uses a modular system that allows you to physically remove these cables – what you should do –, you will need to fasten these cables to help the computer inner airflow.
You can use one of the cable holders that usually come with the power supply, holding all these extra cables together, as shown in Figure 29.
Just place the cables in an empty 5 ¼” bay and that’s it.
Now your new power supply is completely installed and you can screw your case side panel back in place and re-install your computer and enjoy your new power supply. Don't forget to check if the power supply 110 V/220 V switch is configured in the correct position according to the voltage used on your AC outlet.