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Mirror Drive Door HD Bay CPU Heatsink Cooler
By: Matt Vaughan
Posted: July 9th, 2004

MDD Noise Impressions
The MDD Power Mac is a formidable machine. I love the G5s and their quiet cooling systems, but I own a dual processor G4. The G4 is very fast for my needs, and besides, I really like the dual-CD bracket in the MDD. The downside to the MDD is its engineering. My issue is with the variable-speed CPU fan that blows over the heatsink. Unfortunately, Apple didn't line the fan up correctly with the heatsink, so a lot of air is wasted. This results in excess heat, which causes the fan to oscillate at higher speeds after a few minutes of use - especially in the summer months.

Solutions to Loud Fans
Most readers probably know that Apple sent out a replacement power supply and fan kit to the first generation MDD users. The fans in the kit are a terrific improvement over the original fans, but the kit doesn't completely solve the engineering problems of the case. I installed the replacement power supply but opted to replace the 120mm CPU fan with a Panaflo 120mm mid-speed fan, as found at 2CoolTek.com. The only problem I had is that the polarity needed to be reversed on the plug in order to work correctly. After installation, the Panaflo fan was quieter, but the oscillating speeds were still really annoying.

After reading another mod on xlr8yourmac.com (see related links below for many other MDD cooling mod articles), I decided to try to improve the cooling by adding a couple of 60mm fans. I happened to have a pair of Everflo fans that ran relatively quiet, but any 60mm 12V fans should work just fine at either 7V or 5V.

Fan Mod
My goal was to mount the two 60mm fans directly over the aluminum heatsink to provide constant airflow. I also didn't want to make any permanent modifications to the case - I wanted to be able to remove my fans without any hint of the modification. After some searching on the web, I found this hard drive cooler that had an aluminum bracket that fit my needs. It shipped with two 50mm fans in a plastic case, which I promptly thew away. The holes were a little smaller than my 60mm fans, but since I mounted them on raised standoff screws, the extra air around the sides would work fine. I mounted the pair of 60mm fans with 1-1/2" machine screws (8 screws, 6-32 size). Each screw had three nuts - one around the top of the fan, and one on each side of the aluminum bracket. I used a lock-washer on the last screw to keep things nice and tight.

Hard Drive Cooler as Purchased
Hard Drive Cooler as Purchased
60mm Fans Mounted on Bracket
60mm Fans Mounted on Bracket
Raised Standoffs and Spacing
Raised Standoff Mounts & Spacing

Drive Cage
After installing the fans, I wired them in parallel at 7V. This is pretty easy to do with a standard Molex hard drive connector - wire the fan's positive (red) wire to the yellow wire on the Molex connector and wire the fan's negative (black) wire to the red wire on the Molex connector (a Molex connector was included with the hard drive cooler that I dismantled). Effectively, this yields 7V as it is the difference in voltage between the yellow (12V) and red (5V) wires. If that is intimidating, you can wire the fans at 5V by connecting them to the red and black wires on any Molex connector.

Next, I mounted the bracket on to my MDD hard drive cage and eye-balled the necessary depth so that it would not touch the heatsink. Of course, this means that I can't add another hard drive on this drive cage. That's okay with me - I'm not sure I'd want to add another drive near the hot heatsink anyway. After mounting, I bench tested the fans before installing them into my computer.

Fan Bracket Mounted in Drive Cage
Fan Bracket Mounted in Drive Cage

I mounted the drive cage back into the computer and needed a way to discern the depth between my new heatsink fan assembly and the aluminum heatsink. Too much room would mean that the airflow from the fans would simply blow over the heatsink; too little room and the fans might actually touch the heatsink, which would create more noise and possible damage. So, I borrowed some of my son's play-doh and sandwiched some between two sheets of plastic wrap. I then carefully closed the computer and the play-doh accurately showed the clearance between the fans and the heatsink. Note that I did NOT power the computer on while doing this!

After adjusting the fan depths, I wanted to be sure that my new heatsink fans ran as efficiently as possible. I found some foam weatherstripping in the garage and carefully taped it around the fans so that as much air as possible might flow through the heatsink fins.
Play-Doh Clearance Tester
Play-Doh Clearance Tester
Foam Strip Around Fans
Foam Strip Around Fans

I am much happier now! There is a little more fan noise when the computer is first powered on, but the variable CPU fan runs at a more constant, slower speed after the computer is warmed up. I would recommend this modification to anybody who doesn't want to permanently damage their computer case. Ideally, another exhaust fan on the back of the case should be installed to remove more of the hot air around the heatsink, but that might involve a Dremel tool, and I'm not willing to go to that extreme on my expensive and dependable G4.

Other MDD Cooling/Mods and Systems Related Articles:

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