Replacing a Power Supply

Illustrated How to Replace an ATX Power Supply

unscrewing power supply in standard case For people who have never worked on a PC before, the power supply is one of the toughest components to replace simply because of the large number of connections. Laptop power adapters supply power from outside the laptop, so replacement is trivial. The PC power supply I replaced on this page took about 15 minutes, including taking all of the pictures. The first step to replacing a power supply or any other component in a PC is to unplug the power cable from the back of the power supply. The socket for the power cord is above the screwdriver in the picture. The next step is to remove the cover from the case, which varies like crazy from brand to brand. On a standard midtower case like this one, you only need to remove a side cover, the one on the opposite side of the power supply fan grille than the cord socket and switch. The cover is already removed in this pictures (two screws and it slides right out). Finally, we get to removing the screws that hold the ATX power supply in place.

After removing the four mounting screws from the old PC power supply, I moved it out of the way on top of the drive cage. I'm leaving it connected to demonstrate the best method for beginners to replace a power supply. By leaving the old power supply connected, installing the new power supply, and then replacing the leads one at a time, it's nearly impossible to mess up. It's also a good way to replace the distributor cap on an old car if you don't know the firing order. The only thing you have to watch out for is that the old power supply doesn't fall into the case while you're working and damage the motherboard or CPU. Note that our Antec replacement power supply has an intake fan on the bottom, which puts it right next to the CPU heat sink in the standard ATX design. original ATX power supply removed and sitting on top of PC

Installing the replacement Antec PC power supply As soon as the Antec power supply is in place, install the four screws to secure it. The main reason for doing it at this point is you never want to procrastinate securing PC components you install when you're working on a PC or you may forget that they are hanging loose. Then you'll stand up the case and the power supply (or whatever) will drop out of place and bash the fan on the heatsink, or worse. In any case (double meaning) the four screws securing the PC power supply are just to the outside of the cut-out in the back of the case that the fan, switch and power cord socket protrude through. Screws that are further out in the painted areas are case screws.

Now we can begin actually replacing the old power supply connectors with connectors from the new power supply. The most important power connection(s) in any PC are the motherboard connections. The simplest version, as with this Athlon 1000 system, is the standard ATX connector, a single 20 pin (10x2) connector. To remove it, push in at the top of the latch with your thumb and pull upwards on the connector, shouldn't take any real force. If your PC is a newer Pentium 4 or Athlon 64 system, you'll have more than one connector running from the power supply to the motherboard. Both of the newer CPUs usually require an additional 12V header, a 4 pin connector arranged as a square 2x2. High end motherboards like the ASUS with PCI Express can also use the 4x1 drive connectors to supply additional power to video cards by way of the motherboard. Removing the old 20 pin ATX connector from the motherboard

Installing the new ATX power connector The new connector pushes down into place until the latch snaps over the nub. It's a keyed connector, you can't install it backwards, the connectors won't mate. Newer Pentium 4 motherboards, like the one we used for the Socket 775 Pentium 4 in the 4th edition of Build Your Own PC, may have a 24 pin eATX connector instead of the standard 20 pin connector. However, they are usually designed so you can still use a standard ATX power supply with a 20 pin connector and just leave 4 of the pins unmated, and the socket should still be keyed so the connector can only go in on the right side. However, the presence of a 24 pin connector is telling you that the motherboard has a high power requirement, and you'll probably have the option to attach another 4x1 drive connector to supplement power. Also, make sure you take advantage of any power connectors direct to video cards, which reduces the motherboard load.

CD, DVD, and standard IDE hard drives all use the 4x1 power supply connectors, of which the standard power supply will have at least four. Higher end power supplies may have six or eight, and the cables will be longer to allow for use in full tower cases. The connectors and the sockets are both keyed so you can't mate them backwards. However, it can take a bit of force to remove or insert a 4x1 power supply connector, so you want to make sure you are pulling or pushing straight in or out, which the drive designers will make the strong dimension. If you start pulling at an angle on a drive with an exposed circuit card, you could actually damage the drive. Here we're pulling the old (white) connector out of a CD drive. Plugging the power lead into the DVD drive

Plugging the ganged power connector into the CD drive You can see the wire key on the black replacement power supply connector that we're inserting to the CD drive. The 4X1 connector doesn't need to be pushed in with a hydraulic jack. If it stops moving before it looks like it's fully seated against the shoulder, that may be as far as it's going to go. If it doesn't pull out easily, it's probably OK as is.

The trickiest of the drive connections is usually the floppy drive, which uses the small format connector. The connectors are designed with a latching nub which frequently doesn't have anything to engage with, so they can often be pulled straight back by the wires using minimal force. If the connector doesn't want to budge at all, lifting it a little from the facing tab below the four connection pins may release the nub. You can just see it on the bottom of the white connector to the right, protruding a little between the guide edges on the power connector. Below you can see the exposed 4-pin connector and it's open receptacle, and to the lower right, we are jollying the new connector into place, holding it by the wires alone. It would be nice to be able to handle it by the plastic connectors, but in an assembled system, there's's often no room for your fingers when connecting the new power supply lead to the floppy. Disconnecting power from the floppy

Old fashioned power connector Attaching the PC power to the drive

To the right is yet another small format connection, or one more than you'll see in the average system,. In this case, it's a tape drive, and tapes drives often use the smaller format power connectors. Attching power to tape drive

Standard (pre-SATA_ hard drive power connector You've seen enough drive connection to get the point, so I'm showing this hard drive power connection just to point out a few things. You can clearly thee the keyed edge on the 4x1 connector in this picture, cut at a 45 degree angle to the otherwise rectangular drive connector. You can also see where the keyed section ends, which is the maximum depth the connector could be seated before the shoulder would hit the socket.

Our Antec power supply featured far more (and longer) leads than we use in this case, so it makes sense to tie them off with a wire tie to keep them from flopping all over the place, getting into the heatsink fan, etc. I also wanted to show the SATA drive connectors this replacement power supply features. The thin black connector right above my fingers in the picture is an SATA hard drive connector. Finally below, a picture of the installed Antec replacement power supply. Replacing the power supply required removing 6 screws in all, two to release the side of the case and four to remove the old power supply. We secured the new power supply with four screws as soon as we put it back in, which means there should be two screws rolling around on the bed somewhere to secure the case lid. SATA power connectors on Antec ATX supply

Finished ATX power supply transplant Don't replace anything without seeing the ATX power troubleshooting flowchart!
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