|Water Cooled Digital Audio G4 Tower
by Ron Gazaway
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
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.
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
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
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
- 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
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.
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.
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
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
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
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.