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How To Install or Replace an ATX Power Supply

Tech-Tip# 317 By Ryan Morse - May 29, 2011

“…ATX stands for Advanced Technology Extended and is the most common form factor that desktop PCs use today.”

The power supply of your PC is perhaps the most overlooked component of your system. When it’s behaving as it should, you don’t notice it’s even there, but when it starts to fail, your desktop PC can exhibit any number of strange behaviors. If your PC is suffering from seemingly random reboots or doesn’t start at all, the power supply unit (PSU) might be the culprit. In this Tech Tip, I’ll tell you how you can install or replace an ATX power supply in your PC.

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First things first, the power supply unit is a metal (usually aluminum) box that sits in the rear of your PC’s case. It is designed to take the alternating current (AC) from your power outlet and converts it into a stable direct current (DC) that the components inside can safely use. The type of power supply we’re dealing with is known as an ATX power supply. ATX stands for Advanced Technology Extended and is the most common form factor that desktop PCs use today. It comes from a standard developed by Intel back in 1995 that was designed to provide the basic sizing and configuration guidelines for cases, computer motherboards and power supplies. The standard has been modified over time to meet the continued needs of components where, thanks to various modifications, allows the design to be applied to different types of cases and increasing power requirements.

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When purchasing a new power supply, it is important to take in to account the minimum requirements for all of your system’s components. Check with the manufacturer of your motherboard, CPU, and video card (if applicable) to determine what the highest minimum is required.

TIP: I recommend buying slightly over the minimum requirements when you can afford it, generally a power supply unit will perform more efficiently when it’s not being pushed to its maximum capacity, and you may want to leave some headroom for future expansion.

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To install your power supply you will need a Phillips-head screwdriver and a flat workspace. You will also need four screws, but those will either be provided along with your power supply or you can reuse the ones that are in your current power supply. Disconnect all of your peripherals and unplug your system. Start with it laying on its side with its side panel removed, and the motherboard facing up. Disperse any static charge that may have built up on your body by touching your skin to the metal portion of your case.

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If you’re replacing a power supply, your first step is to unplug your current unit from all the components inside. All the wires coming out of your power supply need to be disconnected before you continue. Many power supply connectors are a snug fit and may feel like they are stuck, so don’t be afraid to use a little bit of force. Pay attention when disconnecting the main connector (and optional ATX12V connector) from the motherboard as there is a small plastic latch securing it in place. The only connectors you need to unplug are the ones that lead directly back to the power supply unit, so if you’re unsure if something needs to be unplugged, that’s how you’ll know.

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Once you have all the connectors free, you’re ready to remove the screws. On the back of the case there are four screws holding the power supply. Unscrew them one by one. I recommend using one hand to hold the power supply unit in place as it loosens so it doesn’t clank around inside your case if it slips. Once it’s unscrewed, gently remove the unit, being careful not to bump anything on the motherboard. Depending on the size of your CPU heat sink fan unit, you may need to remove that as well, but that should be a rare instance for most users.

You may just want to just take your PSU out to clean it up. Blasting it with a few shots of compressed air (take it outdoors first!) can alleviate some noise issues that can occur as dust builds up over time.

With your old unit out of the picture, you should be ready to install your new PSU. Gently place the new unit inside the case so that its screw holes line up with the holes in the case. The connection for the AC power cord should be facing to the outside of the case. Plug in each of the required connectors.

Here is a checklist of connections:

    how-to-replace-a-power-supply
  1. One (1) 20/24-pin main connector
  2. One (1) 4/8-pin ATX12V connector
  3. Any required hard drives or optical drive connector(s)
  4. 6/8-pin PCI Express video card power connector(s)

Each connector type is designed to prevent it from being improperly inserted, so it’s really hard to go wrong here. For hard drives and optical drives, use the larger 4-pin auxiliary connectors for IDE drives and Serial ATA power connectors for Serial ATA drives, but do not plug both types into one device.

Following these steps, you should be able to install and remove a power supply from most standard cases, a handy skill for anyone to have.

If you have any question or would like to add any additional feedback be sure to leave us a comment or question!

Happy Computing Folks!

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