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Water Cooled Digital Audio G4 Tower
by Ron Gazaway
Posted: 3/5/2003

Macintosh - It just works.
(Just add water.)

"It just works." That's the slogan. Here's my saga of where it just didn't work. Of course, once you get into the upgrading game rather than just happily paying the cost of a new system, all bets are off and you must be comfortable resolving problems, whatever problems, on your own. Or give up and accept the performance level of your stock system. But what fun is that?

And so it begins. (As documented by excerpts from some emails and project notes.)

Today I received a processor upgrade that I had been waiting a few months to become available. (It had actually dropped a third in price between product announcement and product availability.) The original system is a PowerMac Digital Audio 533mhz dual processor. And the upgrade was supposed to be a 1.2ghzDP. Well imagine my glee when I powered it up and it is 1.33ghz clock rate. Ran a few benchmarks and all looked great. Then it crashed. Bummer. It is overheating. So, do I do the sensible thing and call for an RMA for this defective product? No, not me. I decide that I really like having an upgrade that makes this machine almost as fast as the fastest of the new ones, if I can make it work reliably. [Note: At this point in the saga I didn't know that all these CPU upgrade modules were shipping at the 1.33ghz speed. I assumed a ‘fluke' had landed on my doorstep and I had better keep it.] So, since it can't stay cool enough with the case closed up, I take the approach of moving the bastard off the floor onto the desktop where I can leave it open all the time, with an assortment of extra fans. It's that big heat sink which isn't getting cooled adequately for this 'factory overclocked' job. The other fans are just there since the PCI cards no longer benefit from case flow cooling. [picture 1]

picture 1

The configuration evolved from that in the picture using the single fan supplied in the upgrade kit to having two three inch fans 'pancaked' on top of the heat sink and that is keeping it going. With a full max heat producing number crunching load the thermocouple on the sink measures 17F above ambient. System crashes at 102F. Just the one fan, the one in the picture - the one it shipped with, can only keep it to about 24F above ambient. And the case tolerances are such that that depth fan is the largest which can be installed and close up the case. (I tried <g>.) The extra quarter inch of a full versus half depth fan is just exactly too much for the case to hinge shut. I doubt if the case interior is keeping below an ambient of 80F anyway.

Anyhow, keeping it below 100F it has run for hours under full load and is 2.5 times faster than before. (Actually somewhat more for most usage because of the newer generation PowerPC chip and more cache.) A nice upgrade. At less than half the cost of a comparable performance new machine. (Of course, you can run the new ones with the case closed <GRIN>.)

So at that point I had it running. What was running? OK, here are a few pictures of the PowerLogix Series 133 1.2ghz dual processor upgrade module which you see installed in the Digital Audio PowerMac in picture 1.

picture 2

picture 3

picture 4

picture 5

picture 6

However, I didn't stay a happy camper for long with that solution. While the ganged up three inch fans running at full speed did keep it operational, barely, there were several significant problems with this approach.

  • Marginal thermal conditions — The room the PowerMac is in ranges about eight to fifteen degrees F warmer during the Summer. Air conditioning is more expensive than gas heat. And I like the low to mid eighties.
  • Noise — Move enough air and you get more cooling. And more noise. Much more noise.
  • Open case on desktop — This just ain't right.

So now on to stage two. ‘The Great Air-Cooling Effort'.

picture 7 (Right side view)

picture 8 (Front view - looking down over monitor)

Picture 7 shows three things (of interest) visible here.
1) The original 3in fan removed. 'Custom' duct fabricated from cardboard and shipping tape to mate a 5in fan to a 3in receptacle on top of the heat sink. The foam square squeezes around the fan which is press fitted into the top of the duct and creates an air tight seal. Bottom of the duct is taped around the heat sink to create an air tight seal. All air is forced into heat sink fins. Fan is powered full speed at 12vdc.
2) 3in fan powered at 7vdc blowing over PCI cards for their cooling.
3) Sheet of cardboard (back in chassis) is redirecting air from internal chassis 5in fan (12vdc, but thermal controlled - runs slow/quiet with case open) over the four internal disk drives.

In picture 8 the main thing visible is the 5in fan (at 7vdc) sitting on top of the PCI cards blowing away from the big heat sink. Without this fan there was a substantial re-induction of hot air back into the main heat sink fan.

picture 9 (Right side view)

picture 10 (Front view)

And here in pictures 9 and 10 you see the new 'case annex' fabricated from stacked up old shelving boards. This substantially contains the remaining sound. And the shades closed (as they normally are) also contribute to sound reduction. Zoom in and you can see a sub 90 degree F reading from the thermocouple on the heat sink. (BTW, those digital indoor/outdoor thermometers are great for playing this kind of game and cost about $10.)

After everything settled down I get 91.4F on the heat sink with ambient of 73.0F. Since this room is typically 80-82F in the Summer (which is my favorite temperature range) this would result in about a 102F heat sink reading, assuming linear scaling. Empirical tests have the computer starting to get flakey at 105F as measured at the current thermocouple position on the heat sink. "Walkin' on a thin line."

Noise level is about the same as it was for this system before all these shenanigans started. That is, about the same as the stock G4 Digital Audio.

So, again, I had improved my situation (if you can call it that), but I didn't stay content for long. I knew there was a better way.

A detour through PC land.

I'm quite familiar with the possibilities of, and tradeoffs of, air cooling a computer system. And with my Athlon system I had recently gotten fed up with the noise and hassles involved and made the decision to try a water cooling solution. Enter the "Koolance EXOS - Liquid Cooling System". Hit Google with the appropriate key words and you can find several extensive reviews of this kit on the sites that cater to the Intel/AMD overclocking crowd. Here in the States it can be had for about $300 delivered. A nice-to-have feature on the PC side of this kit makes it pretty much the only viable kit for the PowerMac. That is, it is a self contained kit residing external to the computer case with a PCI card bracket to bring power and water in/out of the case. On the PC side this is merely a convenience since there is usually plenty of room in tower cases to install almost anything. However, there is no spare space in a PowerMac to accommodate a water reservoir, pump and radiator.

picture 11

picture 12

Pictures 11 and 12 show this kit installed on an Athlon 2000+ system. (Which is, yes, overclocked <g>.)

As of today, these are good links for information about the unit. I'm not going to review it again, just show how I've used it.


Now those of you familiar with AMD (or pre-Pentium 4 Intel) systems know that there are a row of three tabs on each side of the CPU socket (socket-462). The most common method of mounting a heat sink on those systems is by a device which hooks over one of more of those tabs. Obviously, there are no such tabs in a Macintosh. Eureka! An adapter is needed.

drawing 1

Now no heat sink made for a single processor AMD/Intel system is going to fit properly on two PPC processors. But my theory was that a copper plate which spanned both PPC chips could be cooled by a water block style heat sink designed for AMD/Intel systems. Since the PowerPC microprocessors heat disspation pretty much tops out at about 25 watts per CPU, for an aggregate max of 50 watts to handle, and the AMD Palomino microprocessor dissipates 70 watts running at stock voltage and speed, I felt on pretty safe ground even if there was some cooling inefficiency due to the intermediary copper plate and an additional contact surface.

Here is what went into creating drawing 1.

I found an engineering drawing of the standard socket-462 socket with detailed dimensions. This was used for the portion of the adapter for the Koolance water block mounting. I measured the relevant portion of the PowerLogix heat sink for its overall dimensions and holes for both mounting the CPU module to the heat sink (in this case ‘water block adapter plate') and for fastening the CPU module + heat sink assembly to the Apple logic board. ‘Extra' (irrelevant to construction) information on the drawing shows the footprints of the Koolance 200G water block (orange) and the two PPC chips (red).

Once I had this drawing (plan, it helps to have a plan <g>) in hand I set out to find a 3.5 inch square by 1/8 inch thick piece of flat copper plate. Which I found locally for $7.03 + tax each. [picture 13] And after only about a half dozen hours of labor with the universal tool (Dremel), and some easy hole drilling, I had an adapter plate fabricated to my custom specifications. [picture 14] (NOTE: Use 1/8 inch drill bit on four ‘outside' holes and the screws supplied with the PowerLogix kit (or any of same spec) will be able to self tap the soft copper.)

picture 13

picture 14

An alternative.

Some Athlon motherboards provide an alternative mounting mechanism of four holes in the motherboard offset around the CPU socket. And some air cooled heat sinks, and more relevantly, some water blocks, are designed to use this form of mounting. Using this mounting technique, requiring only that four holes of proper diameter in the right locations be drilled, would be vastly easier than carving the copper plate to look like an outline of a socket-462. I highly recommend you look into this if you tackle such a project. I only went with this approach because I already had the Koolance kit in house and wanted to reuse it to test the validity of the approach.

For example, in just doing a quick search, this caught my eye:

picture 15: TC-4 Rev 2 Aluminum Topped Waterblock

This water block from D-TEK costs about the same as the Koolance 200G and, if it would work (I see no reason why it wouldn't, I would like to see a picture of the bottom) the different mounting method would make it trivial instead of grueling to make that adapter plate. BTW, the price I mentioned above of $300 for the Koolance EXOS delivered includes the cost of the water block, but the block is in addition to the price of the EXOS itself. In other words, there is no reason not to buy the EXOS unit alone and mix/match another vendor's water block. Caveat, if you do this you do have the responsibility to ensure that the connector tubing inner/outer diameter is compatible with all the pieces.

But that's not what I did. That's what I shoulda done. Now I'll get back to what I did do... (Continued on Page 2)

For other Mac Mods/Conversions and related articles, see the Systems page.

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