Copyright 2010 by Morris Rosenthal -All Rights Reserved
Illustrated How to Replace an ATX Power Supply ( PSU )
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. The PC power supply or PSU 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
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 this 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.
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.
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.
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. You can pick
up an inexpensive Thermaltake 430 Watt for $40 or a 500 Watt Antec for less
than $70. I'd stay away from the $20 power supplies that claim to be putting
out 400 watts or more, but you don't need to upgrade to a 600W or 700W monster
unless you're running dual video cards that are sucking down over 100 Watts
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.
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.
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.