The Original Setup
This is what the insides of my Mac looked like before any of this started. If you look closely you can probably see that there have been a few modifications before this one, mainly as a result of adding the seriously toasty ATI 9800 Pro.
There's one particular oddity in there that you might not first realise. The PCI slot cooling thingy was designed to suck hot air out of the case by pointing the little fans towards hot components. In my G4 it does the exact opposite - it pulls in cool air and dumps it at the front of the case; easily achieved by unscrewing the fans and spinning them around. I tried a standard PCI slot blower fan, but I found that it caused more harm than good.
What would happen is that the air would be rapidly removed from the top of the case, creating a slightly lower pressure and starving the power supply of much needed air for cooling. After a couple of days with a standard blower I found that the grille on the end of the power supply (you can feel it if you stick your finger through the plastic outer casing on the back of your machine) was so hot that you couldn't touch it for more than 10 seconds or so. I classed that as "Not Good", and so I came up with this little solution of reversing the fans on an 'Ultra PC Vent II'. The two 45x45x10mm fans are silent, supposedly shift 15CFM a piece and work wonders at keeping the power supply and the top of the case cool. On this machine they are powered by the unused J3901 pins, which provide a constant 12V output from the motherboard.
Here's a shot of the big copper heatsink, with a couple of additions hiding behind it. This is a very popular modification, which can make a big difference to the temperature of a standard MDD / FW800 machine. In mine I had to add these after case temperatures skyrocketed with the ATI 9800 Pro. As there are no replacement GPU heatsinks that I know of that will fit inside an MDD / FW800 G4 tower (everything hits the optical drive caddy), this really is the best option to deal with extra heat.
This setup was a little Heath Robinson, but had worked very well for over a year. These rear fans were powered from the unused J53 pins, which are not present on all logic boards. If you have them, you're in luck - they provide an OS X controlled variable output, meaning that the speed of the fans is controlled automatically by the kernel extension AppleFan.kext. If you do decide to use these, please be aware that you should keep any load on motherboard pins to an absolute minimum. I have found no documentation on these pins anywhere (a multimeter gave me the first hint at what they did), so what load they can take - if indeed they are supposed to take any at all - must be estimated very conservatively. Having said that, I have run the stock 120mm Papst 440mA fan off them before.
The only other change to the original setup was the replacement of the aforementioned stock Papst 4212H beast with the much more peaceful Panaflo FBA12G12H. If you've got a FW800 or late MDD (the 1.25GHz version Apple still sold for dual-booting to while OS 9 when the G5 came out) then you'll already have quiet PSU fans, so this is the fella to change if you need a dip in volume. That and the optical drive fan - if you can find a decent replacement (which I couldn't at the time).
Time to move on, because it doesn't look like that in there any more.
Dismantle and Clean >>