Replacing a CPU

Illustrated How to Replace a CPU - AMD Athlon

Despite the high clock speeds and high heat dissipation of modern CPU, out-and-out CPU failure is a fairly rare ocurrence. Replacing a CPU isn't particularly challenging if you've done it before, but it can be a little intimidating for the first timer. To avoid endless repetition opening the case, I'm replacing the CPU in the same system I used to demonstrate replacing a power supply and a sound card. It's a 1000 MHz (1 GHz) AMD Athlon in Socket A, a technology that is still be used for some lower cost PCs. Note that upgrading a laptop CPU is rarely possible or cost efficient.

The first step to replace a CPU is to remove the heatsink. All modern CPU's require an active heatsink, a chunk of finned heat-conductive metal with a cooling an mounted on top. The leading cause of CPU failure is probably fan failure, since the CPU can overheat and sustain damage if there's not enough cooling air flowing over the fins. The only rule of thumb for removing heatsinks is to study the latching mechanism then use your thumb to release it.

A standard Socket A heatsink is latched on both sides, but as soon as you release the main spring force by doing the easy side, the other side will fall off as you lift the heatsink away from the CPU. You can see the dried out (not so good) thermal compound on our old Athlon as we lift away the heatsink. You can just see the same dried out crud on the bottom of the heatsink at this angle.

All modern CPUs since the inception of Socket 7 back in the early 90's have used ZIF (Zero Insertion Force) sockets, where the CPU legs are locked in place by moving a locking lever. To remove the Athlon CPU, we first have to release the locking lever and lift it up to the vertical position. The Athlon CPU is then lifted straight out of the socket (below). Also below, to the right, we show the keying on two corners of the socket and the CPU that prevents you from installing it improperly.

The new Athlon CPU we are installing here isn't a new CPU at all, it's a "pull", a CPU that's been removed from a system. When you shop for a replacement CPU to install on an older motherboard, you'll see that the prices are super low and most are identified as "pulls. The Athlon is installed in the socket and locked into place with the locking lever, which is pulled a little away from the side of the socket to get past the locking nub.

Now comes the critical step. All modern CPUs require some sort of thermal material be added to the die to improve the thermal interface with the heatsink. The purpose of a thermal compound, like this Arctic Silver Ceramique, is to fill in the microscopic voids in both the CPU die and the metal bottom of the heatsink. You down't want to drown the CPU in thermal compound, just use enough (many manufacturers define the amount as a large grain of rice or a small pea) so when the heatsink presses down on it it will spread it over the die.

That's it, time to reinstall the heatsink by first latching the far side of the retaining spring over the center nub on the opposite side of the socket. You can see it latched on here between the capacitors, which makes this the "poor access" side and the reason we install the CPU heatsink retainer on this side first.

Next we do the hard side, which we've mad a lot easier by pulling the power supply first:-) With the active heatsink in place, the final step is reconnecting the power to the heatsink fan (below) to the CPU fan point on the motherboard. It's critical you connect it to the proper point which the BIOS manages for low power and sleep modes.

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Don't replace anything without troubleshooting first!