iMac G5 CPU Fan

Overview

This is a brief guide for how to replace the very loud CPU fan on some of the iMac models with a very quiet larger fan. This has actually been a very well trafficked post, but I'm guessing it will start to die off as the old models go away.

Modification Steps

Pretty simple, but definitely not for the faint of heart:

1. Take off the back cover of the iMac case
2. Remove the CPU heatsink cover(It has a big G5 emblazoned on the front). You should be greated with a big set of copper fins. There are some small tricky tabs that hold it in place. Also mine came completely off, but apparently some versions have to be cut off
3. Find the CPU fan connector on the motherboard and unplug it, plug in your new fan and test it. But my version didn't have a CPU fan plugin(Trust me I checked and unplugged everything several times), so I forcefully removed the CPU fan(it's towards the bottom) turned on the computer really quickly, used a multimeter to check which leads were positive and negative(It had 3 wires, one is for speed sensing I think), and then cut the wires on my fan and spliced them in.
4. Next I marked on the back where to cut for the fan(Directly over the heatsink) and cut it out with a Dremel
5. Finally mounted the fan to the back over the hole and put everything together again

Pictures

    

Conclusion

The computer has been running over 3 years now with no problems. It is cooler than it was with the stock CPU fan, so the modification should prolong the life. It is going at about 60C(140F) after being in use for a while. The maximum temperature a PowerPC G5 processor can run looks to be about 75-80C(~170F).