Starting the procedure

Set the iMac monitor-down on a soft towel. Remove the processor and hard drive chassis from the bottom of the iMac, and set it on your workspace. See iMac2Day's visual guide to RAM upgrades for some photos of chassis removal.
You can dissipate static electricity in your fingertips by touching the metal sides of the chassis; this is probably a good thing to do before you begin touching the boards, and after you get up and move around every time. Be sure to follow anti-static procedures; you may want to invest in a grounding strap from your local computer supply store for a few dollars.

• Remove the RF cage from over the processor card.
• Remove any extra memory card you may have installed in the upper memory slot.
• Remove the heatsink from the processor card by prying out and up on the retaining bar. You may need to bend the side of the metal cage in a little bit with your other hand to get it to pop off.
• Remove the processor card from the chassis; the best way to do this is to pry gently and repeatedly with a small flathead screwdriver along the edge that is farthest away from the processor (toward the back of the iMac); don't worry; it will pop up eventually.
• Remove the memory module from the lower RAM slot.

	This is the iMac chassis immediately after being removed. The sliver metal grid is the RF shielding; you'll need to remove it in order to get at the heatsink & processor card. It will pull right off. If you install a larger heatsink & fan, you won't be able to re-install it, so you may get some interference with radios, TVs, or other electronic devices.
	Not the best photograph, but you can see the heatsink and the metal retaining clip. Use a set of small needlenose pliers to pry off the clip. The heatsink will simply lift off after that.
	This is after removing the retaining clip, heatsink, and my extra memory module. Note the screwdriver; this is where you need to pry (gently, in small increments, and along the whole edge) to get the processor card to come out.

You now have the processor card out; flip over to the side opposite the processor (the same side that the stock memory module was in). Look in the corner for a set of resistors labeled "R117" through "R124". They're very small, and the white text labeling them is off to their left. These are the ones you're going to have to move around to reconfigure the iMac to operate at a higher speed. Below you'll find a link to a chart of which arrangement of resistors will result in what processor speed. I am not aware of a technique to increase bus speed on the iMac, and at any rate that is probably not a stable modification to make nor one which will result in a large performance increase. A faster processor speed will make a much more significant difference.

Fasten the processor card down to your desk with tape, or some similar method, to keep it from moving around while you're trying to work. Pictured below is the underside of the card, where the resistors are. They are in the lower left corner as you look at this picture. The checkbook was about the right thickness to keep the card from rocking.

I received an e-mail from a reader who warned about a ptifall with this procedure that I was unaware of: using adhesive tape can generate static electricity! It is apparently generated when you unroll the tape, and could zap components if you do what I did in the picture below. I was lucky. The reader suggested using conductive foam or a similar material between the processor card and the tape if you choose to hold it down with a method like this, or using a "Pana-vise" (I must confess I don't know what that is). Thanks, Rob.

See this page for a photo of the stock resistor layout, as well as charts that illustrate which layout will result in what processor speed.

Probably the best way to lift off those resistors is to have two people, a pair of tiny needlenose pliers, and two soldering irons, or better yet, soldering pencils. One person heats up both sides of the resistor simultaneously, the 2nd lifts with the pliers and sets it into the new position, then the soldering iron person fixes it back into place. This is obviously not possible for everyone.

What I did was this: I positioned my pliers so that I would basically be levering the resistor out of the way when I pushed on it, then I quickly touched my soldering iron to each side before pushing (gently) on the pliers.

Then set the soldering iron off to the side while you nudge the resistor into its new position. Hold it down by pushing on it with the pliers, and touch the soldering iron to each side to make the connection again.

Be patient, be careful, and take your time preparing. Be sure not to spend too much time heating up the resistors, as what can happen (and did happen to me) was that part of the trace (the actual path that's etched into the silicon board) will lift out of the board when you apply heat for too long. If that happens, it's not irreparable, but it's not easy to fix. The trace on my board stayed intact, and I was able to fasten the other side of the resistor back down; how long this will last I don't know. If and when it breaks, of if yours does, it can be repaired (generally) by connecting a length of tiny wire from the resistor to wherever the other end of the trace is. This probably takes even more skill then moving the resistors around, so this might be a repair where you would need a skilled electronics person.

The value of the surface mount resistors is 1K, should you damage or lose any of them. Thanks to Jörg for that piece of information!

Note that it should not be necessary to add more solder to the connections. If you think this is necessary in your case, only do it if you really know what you're doing. With parts & connections this small, it would be very easy to create a short among the resistors, rendering your processor card useless.

Don't forget to put your lower memory module back in before re-installing your CPU card!

Now that the first hard part is out of the way, it's time to discuss the second: cooling.