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How to Replace Your Desktop PC’s Power Supply

You can’t repair your desktop PC’s power supply, you can only replace it. Don’t ever open your computer’s power supply or try to fix it yourself. Remember — replace, don’t try to repair. The power supply stores powerful jolts of electricity, even when the computer is turned off and unplugged. Power supplies are safe until you start poking around inside them.

1

Turn off your PC, unplug it, and remove your computer’s case.

Locate your PC’s old power supply sitting in a corner of your PC’s case. The power supply’s back end fits snugly against the back of your PC so that its built-in fan can blow out the hot air. On its other side, dozens of colorful cables flow from a small hole.

2

Make sure the new power supply’s cables will plug into the correct spots by putting a strip of masking tape on the end of each plug and writing down its destination.

Each cable ends with one of several types of plugs. The plugs are shaped differently to mesh with their particular connector.

3

Unplug the power cables from the motherboard (the large, flat, circuitry-and-slot-filled board).

Two power supply cables plug into the motherboard: one pushes into a large, 20- or 24-pin connector (left), the other pushes into a smaller, 4-, 6-, or 8-pin connector (right). On motherboards set up to run two video cards, you’ll also remove a four-pin connector that looks just like the ones plugging into older CD/DVD drives (see Step 4).

4

Unplug the power cables from the hard drives and the CD/DVD burners (new on left, old on right), as well as any other places on the motherboard.

Motherboards usually include small four-pin connectors for controlling switches and fans. Your old power supply will probably have some dangling cables that don’t plug into anything. (Those cables are thoughtfully supplied to power any future upgrades.)

5

Remove the four screws that hold the power supply to the computer’s case.

Be careful not to remove the screws holding the power supply’s internal fan. To see which screws are which, try loosening the screws slightly and wiggling the power supply from inside the case. Also, the screws that hold the power supply in place are generally closer to the outside edge of the computer’s rear. The screws that hold the fan are generally closer to the fan’s edge.

6

Lift out the power supply.

If the power supply is cramped, you may need to loosen the screws holding some drives in place and pull them forward a bit. If the power supply still won’t come out, make sure that you’ve removed all the screws. Some power supplies have extra screws around their base to hold them down.

7

Buy a replacement power supply.

If you can’t purchase a replacement power supply online, take the old one to the store and look for a replacement. If you’re planning on adding more computer gear — a powerful graphics card, more hard drives, or more DVD burners — buy a power supply that has a higher wattage.

8

Plug your new power supply into the wall before installing it, just to listen for the fan.

If the fan doesn’t work, return the power supply for one that works. If you do hear the fan, though, unplug the power supply before beginning to install it.

9

Make sure that the power supply’s voltage is set correctly, if necessary.

On the back of some power supplies, near the fan, a red switch toggles the power to either 120 volts or 220 volts. If you’re in the United States, make sure that the switch is set to 120 volts. If your country uses 220 volts, flip the switch to the 220-volt setting.

10

Place the new power supply in the old one’s place, and tighten the screws, then reconnect the cables to the motherboard, the drives, the fans, and the power switch.

Look at the masking tape labels you put on the old power supply’s cables. Remember, some cables won’t connect to anything; they’re for future add-ons.

11

Reconnect the power cord and plug your computer back in.

Its power cord should push into the socket near the fan.

12

Turn on the power and see whether it works.

Do you hear the fan whirring? Does the computer leap to life? If so, then all is well.

13

If the fan is not spinning, try plugging a lamp into the power outlet to make sure that the outlet works.

If the outlet works, exchange the power supply for a new, working one.

14

Turn off the computer and put the case back on, then turn the computer back on.

Is everything still working right? If it is, put a cool glass of iced tea in your hands. Congratulations!

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