Fan Modifications(iMac G5 and a random case) -- /dev/random

Fan Modifications(iMac G5 and a random case)

Overview

Two very different fan modifications. One to replace the incredibly loud stock CPU fan on an older version of the iMac G5 with a very large lower speed fan, and another to add extra cooling to a small cube computer I have.

iMac G5 Modification

Pretty simple, but definitely not for the faint of heart. I followed the basic premise found here.
Here's the entire process in a nutshell:

Take off the back cover of the iMac case
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
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.
Next I marked on the back where to cut for the fan(Directly over the heatsink) and cut it out with a Dremel
Finally mounted the fan to the back over the hole and put everything together again

Pictures below(Click for bigger size):

I used one of the new(At the time) liquid bearing fans, but got a higher RPM one. I think if I had to do it over I'd get 2 quieter lower RPM fans.
Also, a quick note against the design, the entire problem stemmed from the thin case, since they didn't want a CPU fan directly over the CPU they put it underneath and made it blow through. The issue is the fan was incredibly small for a CPU fan and thus had to go at incredibly high RPMs to get the proper air flow. My understanding is that newer versions of the iMac don't have this problem(Not sure if the design was changed, or just used a better fan), but I don't know how it ever got out of QA testing when it was so horribly loud.

Update

Someone wrote in asking about lifespan and temperatures. The computer has been running over a year 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).

Cube Computer Fan Modification

Really the main reason I'm putting this up here is to say use a hole saw if you don't have good tools to make a circle. I've seen people cutting them with Dremels, or doing several holes with a drill. I tried these on a scrap computer case with absolutely horrible results. The easiest solution I found was to use a hole saw, which makes a perfect circle with nothing more than a handheld drill. Pictured below:

I did have to cut some metal with a Dremel on a drive holder to get the fan to fit inside. Pictured Below:

And then I secured it on the inside using hot glue and duct tape :( Obviously not the proper way to do it, but it works, and I was being lazy. A better way would have been to put the fan's grill on the outside, buy longer screws that fit, and then drill holes and secure it all together. Finished product pictures:

Comments(1) 2008-12-16 14:16:31

(2008-12-07 13:53:54) Steve said:

Hi Gavin,
Thank you for the fan mod info.  Could you give some suggestion how to get the
original cpu fan out?  I pull up on the metal tab, it\'s loose, but I\'m
afraid of breaking something.  If the midplane needs to come out, any good
directions out there?  Thank you so much.
Steve
ssobiech at yahoo dot com

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