The PSU, which converts standard AC current into multiple, different low-voltage DC power feeds and supplies them to various internal PC components, is the most fundamental—and overlooked—component of the PC. Without it, you can do nothing—not even run boot diagnostics.

While the scenario described above almost certainly indicates a dead PSU, other, less-easily-pinpointed symptoms can crop up days, if not months, before the PSU goes kaput.

Many symptoms of a failing PSU have other causes, as well, but you can eliminate some possibilities and then test it to determine if it is outputting properly. If you find problems, even if the PSU hasn’t hit “brick” stage yet, you should replace it. To learn more about evaluating possible PSU failure, refer to the “Identifying Problem PSUs” sidebar in this article. For tips on purchasing a new PSU—an important task not to be undertaken lightly—refer to “How To Spot A Winner.” If you’re ready to dig right in, read on.

Replacing a PSU and dealing with electrical current may seem like a scary operation. In reality, it is no more dangerous than other internal PC work, provided you are careful. The greatest danger when you replace any PC component is to the delicate transistors and circuits on the PC, not to you.

Safety First

Before you begin, taking several precautions will avoid frying your PC for good. Our bodies can discharge huge amounts of static electricity. Don’t stand on a thick rug or wear fuzzy or polyester clothing.

Consider purchasing an antistatic wristband from your computer store or online from companies such as Belkin (www.belkin.com) for under $10. Optionally, keeping your hand in contact with an unpainted metal surface during operation will help.

1. Get ready. Grab a Phillips-head and a flat-head screwdriver, a bowl to hold screws, and a pad and paper—or a digital camera if you have one. Shut down your PC and all peripherals. Unplug all power cords and disconnect all devices from the PC. As you do this, make a note or take pictures of what attaches where for later.

2. Take your position. Place the PC on a well-lit, clean, low-static surface such as a wooden kitchen table. Locate the screws that hold the computer cover or panels in place—there may also be tabs you press to release them. Remove the cover or access panels. Ensure the interior isn’t filled with dust or pet hair, which could be overheating your PC. If it is and the system has been acting erratically, a good cleaning might resolve your problems. (Make sure you’re properly grounded and use appropriate cleaning methods, such as gently blowing off the dust with canned air. Brushes and other cleaning tools can generate damaging static.)

3. Identify the PSU. It will be a large metal box with a fan grille on one side that connects to the motherboard, the hard drive, and other powered components inside the PC. Making sure you are grounded as described earlier, trace the bundles of wires that lead from the power supply to the PC’s internal connectors. Note what goes where.

4. Disconnect internal cables. Grasp these connectors by their plastic ends and gently pull them loose (you may have to depress clips). Do not pull directly on the wires. Note that in some cases, you may find it is easier to pull the PSU out first (Step Five) if the connector wires are long enough.

5. Extract the PSU. Remove the mounting screws that hold the PSU in place, but not the ones that attach the fan grille to the PSU. Look for a mounting bracket and remove it if necessary. Carefully remove the PSU from the case. If you need to test the old unit to make sure it is bad, do so now.

6. Install the new PSU. Unpack the new PSU. If you haven’t previously done so, check to make sure the new PSU is an appropriate replacement for the old one. If the PSU is cold, let it come to room temperature. Place the PSU in the same position as the old one, making sure it fits comfortably. (If you removed the PSU before you disconnected cables in Step Four, reconnect them as described in Step Seven before you place the PSU.) Use the mounting screws (and bracket, if present) to fasten it down.

7. Connect the PSU. Keeping yourself grounded, reconnect the PSU cables by holding only the plastic ends. You will need to push firmly, but if you feel like you have to force one into place, you may need to rotate it 180 degrees. Pay special attention to placement of the motherboard cable if it has a 20-pin connector.

8. Perform a cable check. Make sure that no cables or unused connectors are touching the processor fan or any other moving part. Bundle loose cables and place them so that they will not become tangled up in the fans when you return the PC to its upright position.

9. Replace and restart. Replace the case or access panels and resecure them with the clips or screws you set aside. Return the PC to its original position and reconnect all external devices as they were. Restart your PC. If everything starts normally, you’re done!

Final Thoughts

Power supplies and other PC components are rated for years of use, but overheating from dust and hair, overloading from high-power devices, and fluctuations from dirty power or power surges can shorten that life. If you discovered any of these issues while troubleshooting, promise yourself now that you will change your ways. And if you don’t have a top-notch surge suppressor, consider purchasing one.

by Jennifer Farwell