Reassembling the iMac

Now fasten the board on the side back in, install the Bondi Blue cover and the faceplate. Turn the iMac over so that it's resting on the monitor. Roll up a hand towel and put it under the bottom of the monitor, about where the case says "iMac". Set the bottom part of the case in place, but don't fasten it down yet. The trick to getting the chassis back in with a tall heatsink & fan is to pull the bottom part of the case out while sliding the chassis in; it creates an extra couple of inches of clearance.

Note that you will get more effective cooling from your heatsink & fan combination if you leave off the blue plate which covers the side with all of the ports. I'm talking about the whole side, not just the little expansion port blanking plate. There are just two screws holding it on; undo those, and then pull the top out & down (the bottom almost acts like it's hinged). The only two precautions I can think of after leaving this cover off are 1) you may get more RF interference, and 2) you need to be gentle when plugging a phone cord into the modem, as it's not as solid as it was before. All of the other ports are still solid. Plus, you can get to the reset button very easily now!

If you close the expansion bay door, you can barely see that the blue plate has been removed.

Be careful, take your time, and get somebody to help you out while you slide the chassis back in. Once you have the chassis in place, go ahead and fasten down the bottom part of the case. It may be a little tough to get the two screws at the back in, as the chassis interferes with them slightly, but with a small pair of needlenose pliers and a small phillips screwdriver, you can do it. Take care not to drop them into the case.

You should be at the point now where you can put your iMac proper-side up, plug in your keyboard, mouse & power, and turn it on to take it for a spin.

Powering it up

After disassembling your iMac and mucking with the innards, it may take a lot longer to startup the first time than it did in the past. You should hear the familiar startup chime right after you press the power button, but then it may take the better part of a minute for the gray screen with the happy Mac to appear.

Use a utility like PowerLogix' SpeedMeter to keep an eye on your processor temperature for several hours; mine holds steady at 51 C / 123 F if I leave the expansion bay door open, and will go up to 55C / 131 F if I close the expansion bay door. This is still running cooler than my factory-original iMac was.

You can try changing the backside cache ratio with a piece of software like PowerLogix' G3 Cache Control; prior to clock-chipping, I had mine running at a 3:2 ratio, or 155 MHz. After clock-chipping, my iMac would hang when it got to the G3 cache Control during startup, so I knew my backside cache chips couldn't handle a 3:2 ratio at 300 MHz (meaning the cache was at 200 MHz). I bumped the ratio down to 2:1, which is the stock ratio, and a speed of 150 MHz, and everything was fine. Your cache chips might not be able to go this fast, and if you try bumping your iMac up beyond 300 MHz, you may have to settle for a slower cache ratio like 5:2 or 3:1. This won't have a huge impact on performance, though -- the increased processor speed will more than make up for it.

PowerLogix still has a beta posted of AutoCache, an extension which will -- according to the documentation -- analyze your cache chips at startup and automatically select the highest possible ratio for your machine. Note that this is beta software, i.e. you take your chances using it, and it will expire. That having been said, it worked well in my iMac for several hours and a few restarts, and each time selected the highest ratio I was able to get using other utilities. It's still in beta testing after many months, though, so I would have to recommend using a different utility.

Some people have reported trouble with G3 Cache Control causing freezes during startup only intermittently; one of these users reports that these problems went away after he switched to a different piece of software to control his cache, the G3Strip. This is shareware where PowerLogix' software is free, but gives you a nifty, customizable readout in your control strip. If anybody else has success where there was failure before, please tell me.

If you try a ratio that is too high, and your iMac hangs when it gets to the cache control software icon during startup, restart it with the reset button and startup with extensions off (hold down the sihft key). Open your cache control software and select a slower ratio, then restart.

Now for some information on what kind of results you may see.