Tuesday, August 08, 2006

4: Replacing the 120 mm Main Cooling Fan

Quite possibly the most important part of the entire MDD enclosure is the 120 mm fan that in the stock configuration is the single primary source of cooling for the internal components of the Power Mac. Given it's importance, you'd expect Apple to use the most powerful and most efficient type of fan that it could, and indeed it did. In the original version of the MDD released at the end of 2002, the 120 mm fan used by Apple was the infamous Delta AFB1212SHE. At 3700 rpm, it blew out a phenomenal 151.85 cfm, @ 53 dB, making it a screamer - quite literally. In fact, the Delta was quite likely the single most aggravating factor of the first MDD G4s that led to the measures that Apple took to remedy the situation.

Aside from the improved power supply fans, the centrepiece of Apple's solution was the 4212H, made by the European company Papst. Its specs: 3400 rpm, with 108 cfm @ 4 9dB. At this point I can only surmise that Apple came to the realization that the cooling envelope afforded by the Delta could be narrowed down comfortably by using a slower, quieter fan. It would seem then that Apple had apparently overengineered the cooling system on the first MDDs. Circumstantial evidence of Apple "overclocking" the G4 CPUs on these Macs (as originally alleged) perhaps?

The later model FW 400 MDDs released in June 2003 had the Papst fan, as did their OS X-only/FW 800-equipped sister models released earlier. Apple seemed to make a significant improvement to the noise situation (aided in no small part by the replacement power supply fans which accompanied them), but nevertheless, while 49 dB is lower than 53 dB, 49 dB is still 49 dB. Was a better solution out there?

Many 120 mm fan replacement projects that I'd read about on places like MacMod and xlr8yourmac involved the use of quieter fans running at slower speeds (i.e. less rpm's). But of course, with less rpm's comes a lower cfm rating. The prevailing logic behind the use of slower fans was that since the electricity on the 120 mm fan is directly regulated by the OS itself, it seldom, if ever runs at full speed. And yes, apparently my MDDs fans right now are not running at full speed - a lesson I was to learn later on. Anyway, since the fans don't run full blast (or rarely ever do), you can get away with running a slower fan, since at its maximum speed, it would be running at about the same level that the stock fan would when its "regulated". Correct me if I'm wrong, but that's the general impression I got.

I didn't feel good with that. I needed a fan which met if not exceeded the specs of the stock fan (in terms of airflow), but with a lower dB rating. Searches among the usual suspects (Thermaltake, Antec, Vantec, etc.) proved fruitless. But eventually, I found it.

Photobucket - Video and Image Hosting

I'd read in some places that a specific fan made by Panaflo (owned by Matsushita, aka Panasonic) was one favoured brand of fan that both ran quiet and ran well. Usually, the "Medium" type had been used, but its specs didn't match up to the Papst. But one type did. Panaflo's "Ultra" type is to my knowledge second only to the original Delta for cfm rating. I'm sure there are other fans out there with better specs, but the Panaflo Ultra was the best I could find in my research. And luckily, it was available at Bigfoot Computers. At 2750 rpm, it puts out 114.7 cfm @ 45.5 dB.

If you order from them (they're a GTA-based outfit, but they'll ship throughout Canada, I think) they'll ask if you want a 3-pin or a 4-pin Molex connector. Get the 3-pin connector. However, if you'll look at the original connector, you'll note it's a two-pin type. That's because standard case fans usually come with three wires: two for power, and one connected to a temperature sensor or an rpm sensor on board the fan. The third pin's connector leads to circuitry on the motherboard which uses the information on the sensors to regulate the power going to the fans. On the MDD, it's not done that way. Power regulation to the fans connected to the motherboard is done via the OS itself, through a .kext file that you can actually modify yourself. Therefore, the third pin isn't needed. Don't worry, though; the 3-pin socket on the fan (which I'll just refer to as the "connector" for convenience's sake) is physically compatible with the 2-pronged outlet on the motherboard (which I'll just call the "plug") - the two pronged outlet is just two wire prongs, and the securing tab is narrower than the fan connector (2-pin and 3-pin connectors and plugs are identical, just that the 2-pin variants are narrower).

In short: just plug it in. But before you do, look at the wiring on the Papst. You'll notice that the "Blue" and "Red" wires seem to be swapped compared to the "Black and Red" wires on the Panaflo. I don't know why this is, but you don't need to change it: here, "Blue" on the Papst is equal to "Red" on the Panaflo, and "Red" on the Papst is equal to "Black" on the Panaflo. This means that you don't need to swap the wires on the connector.

Installation is easy. Open up your Mac, and remove the optical drive assembly just as you would be if you were going to change or upgrade the Super/Combo drives that came with your Mac. Then, lift up the Papst from its socket. It's not even screwed in place; just pull. There are very small and shallow notches on the bottom end of the fan, which correspond to the metal tabs on the fan bracket. If you don't feel like making your own notches by using a Dremel tool or a file, you can just lightly bend the tabs outward to accommodate the fan with some needle-nose pliers. It'll be a very tight fit, but it'll go in. And that's that.

Just for kicks you can experience what this fan can do at maximum speed if you hook it up to an unregulated 4-pin Molex power connector (through an adaptor). I tried it myself and the noise was so loud that it was literally deafening - I could hear it all the way from my room to the kitchen. But I did notice that Temperature Monitor reported an almost 15 degree drop in my CPU temperature...


Post a Comment

<< Home