We need to get this 9600 cooling issue clarified so people don't burn their computers up.
The principle of computer cooling is that (1) air must be drawn in somewhere near the bottom of the case, (2) air must be blown over the parts that need cooling, and (3) heated air must be exhausted out somewhere near the top of the case because (A) Heated air wants to rise and the easiest and most efficient way to move it is up and (B) Crucial parts in a computer that run hot, ie hard drives, processor, PCI cards, must have air flow over them to carry away excess heat.
In the case of the 9600 the large (120mm) side door fan is placed down low on the side door and (in later models) a plastic shroud is used to assure that air drawn in does not go back out of the door vents (which are little round holes all the way along the bottom edge of the door) but goes upward into the upper box as it should . The fan itself is placed so as to blow the incoming air over the parts most in need of cooling. In a stock machine this is the PCI cards and the processor. And, if you add two hard drives to the black plastic drive mount plate, these two hard drives will be directly in front of the fan so that they also are cooled by the incoming air flow. If you look inside the 9600 case you will see that it was designed so that this incoming air flow would be directed to these areas that need cooling.
When upper box portion of the 9600 case is locked down there is space behind it to accommodate the motherboard and there are holes in it, both on the bottom and back, on the motherboard side, to allow air to move upward and into it. Yes, these slots and holes can get crowded with cables, and that is why I put a larger fan on the outside of the case, directly over the power supply fan, to increase the flow of air up into the upper box portion, draw more air out through the power supply, and exhaust heated air with more force out the back of the computer.
If you set up a 9600 with both fans blowing air out of the case you simply do not have the needed incoming air flow. Incoming air will have to seep in around the cracks in the front faceplates and the PCI slots, which are too small to allow the volume of air needed and do not direct the incoming air onto the crucial parts that need cooling.
The Avid system came with a new side door for the 9600 which has a more powerful 120mm fan in it and which blows incoming air directly over the PCI slots to cool the Avid PCI card.
If someone has a 9600 with the 120mm door fan mounted backwards so that it is exhausting air through the side door vents, that is certainly their privilege. And if it works for them, great. But I cannot emphasize enough that the 9600 was engineered and designed to draw air INTO the case through the side door vents, move it upwards into the upper box and exhaust it out the rear through the power supply. There are upgrade variations one can add to this principle, but the principle of drawing air in low and exhausting it high must guide any modifications for proper cooling.
More principles: It does little good to move heated air around inside a computer case. If you want to improve cooling you must bring air in from outside, move it over the parts that need cooling, and exhaust it somewhere. And cooling fans have to be cleaned periodically because they lose efficiency as dirt builds up on them. In the 9600 I take the power supply out and use high pressure air spray and Q-Tips to clean the fan and inside the power supply.
I have 8 highly upgraded 9600's and I have studied 9600 cooling issues extensively. I plan for at least some of my 9600's to be around for another twenty years, so that people who want to access my graphic archives can fire up a 9600 and print them out. I have made an extensive study of the inside of the 9600 case.
If you don't have the money to replace your stock fan, take your old 120mm side door fan out, clean it, and put it back in so that it draws air INTO the case. After you start up your computer, place a piece of paper over the side door intake vents. The intake airflow should be strong enough to suck the paper firmly against the door. If the old fan doesn't hold the paper tightly to the side of the case or if you have added devices to your 9600, buy a more powerful (6 Amp) 120mm fan and replace the stock fan. Be sure to plug it into one of the power supply connectors. The stock fans in existing 9600's are getting old now and newer, more powerful fans are readily available. Replace your stock fan before you burn up a hard drive, not after.
You certainly make a good argument for orienting the side fan to blow air into the case. It does indeed make more sense to move the warm air out the top and have cool air enter from the bottom due to the laws of convection.But Apple didn't seem to design it this way.
Here's one test I conducted:
System specs:
9600/350 upgraded with xlr8 ZIF Carrier (G4/450 processor.) Cooled with a Tennmax Lasagna Thin heatsink fan, with Arctic Silver III applied.
768 MB RAM (6x128 DIMMs interleaved)
30 GB 7200rpm Maxtor IDE hard drive mounted on the bottom platter.
Stock internal 24x SCSI CD-ROM
Internal 8x4x32x SCSI CD-RW
Internal ZIP drive
Floppy drive
PCI Cards:
Sonnet Tempo ATA66 card
Voodoo5 5500 graphics card (very hot card)
Soundblaster Live! card
Belkin 2 port USB card
Generic 10/100 NIC
(Usually there is also a Radeon 7000 graphics card installed but it is temporarily in my DA G4 frankenmac until I buy an AGP card for it. The idle temperature of the processor is the same with or without it installed.)
I used Gauge Pro's memory tester to work the system out. Though the G4 isn't known for giving accurate temperature readings, the difference is what I was most interested in.
Side fan blowing air out of the case:
Idle temp: 38C Running temp: 46C Average time to return to idle temp: 79.0 seconds
Side fan blowing air into the case:
Idle temp: 38C Running temp: 46C Average time to return to idle temp: 90.3 seconds
This indicates that the processor reaches idle temperature faster with the fan blowing air into the case, but overall the temperatures are the same. I don't have any temperature sensors installed in the 9600, so there isn't much else to test.
Problems I see with having the fan oriented to blow air into the case:
*Why aren't there venting holes between the lower and upper sections? If all of the air is supposed to move from the lower area to the upper section, why are there only a few small cutouts for cables and the odd hole here and there?
*Why is the power supply exhaust fan smaller than the side door case fan? They should at least be of equal size, or better yet the power supply fan larger since there are multiple intake vents. It seems like there would be an overpressure, and air would end up escaping out other areas.
*One noticeable difference when I switched the case fan to blow air into the case is that there is very little air being drawn into the opposite side and bottom intakes. When the case fan is mounted to blow air out, there's a significant amount of air flowing into these intakes. Now if the power supply fan was larger and drew more air than the case fan, there would probably be more air moving through these intakes.
*There didn't seem to be any more air blowing from the power supply than when the case fan was mounted to blow air out the case. If it is starved for air when the case fan is blowing air out, why isn't there a noticeable difference?
I'm not saying that having the side case fan blow air is any better or worse, it's just that I received both the 9600 and the 8600 case I transplanted a G4 logic board into, the case fan was oriented to blow air *out* of the case. In both machines the IDE hard drives are mounted on the bottom platters, and in both the drives are barely warm to the touch. I've never had any problems in either.
Everyone on the List who has an 8600/9600, please chime in what model it is and whether the side case fan is blowing air in or out.
-RPM
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