Cooling Digital Audio Power Mac G4? CPU is roasting!

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Cooling Digital Audio Power Mac G4? CPU is roasting!

G4 7455B @ 1.467 GHz
OWC Mercury Extreme

I just got a Radeon 9700 Pro for my system. The system started locking during stress tests (Quake 3 timedemo loops). I first thought it was the video card. After all, the system *was* stable before putting it in.

I first questioned the 9700's timings, but underclocking the video card 10% didn't help.

I left the case open though, and the system was fine.

It seems the CPU is overheating. Inside the case, the CPU is blocked on all sides. PSU right above it, the case on around it, and the one location it was getting air now has a video card blocking it.
The problem started when I put the 9700 Pro in because of its *size* and not the functionality of the card.
With the side closed, the video card blocks the intake fan enough to seriously reduce case air-flow.

I had only used GeForce2 MX cards and a GeForce 6200 card. Both lower profile cards that allows cool air coming in to blow against the CPU. The 9700 Pro barely fits, and blocks most air.

So, how do I cool this thing?

I have one or two 40mm fans, a few 80mm fans, and one blower.

There are holes on the back of the case behind the CPU. Should I put a fan on the back of the CPU, pulling in air from the back?
Should I put a fan on the front of the CPU, blowing air out towards the holes?

Should I pull the two little 40mm CPU fans off, and put a bigger (80mm) fan on top of the CPU's heatsink?

Should I place some fans from where there is airflow (under the video card) and try to blow it to the front of the case, hoping to get some air moving to where the CPU is?

I saw one image on some other site showing a "blow hole" mod. I'm sure pulling out the hot air on top will help a lot, but I wanted something that didn't look so horrid.

I've been running the CPU at just 1.33 GHz to try and cool it down.

eeun's picture
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There's not too much room to

There's not too much room to play around the CPU. You've already got the Mercury's two fans blowing, so if it were my system, I'd be looking at getting air from outside the case to the CPU's fans.

The way the G4 circulation is supposed to work is the 120mm fan pulls air in from the bottom back of the case, and it flows to the front of the case, up, and across the CPU and out those holes behind the CPU. A lot of the air that comes into the case ends up going out the PSU instead. So a combination of the faster G4 and the larger video card ... well, you already know it's no good.

If you want to preserve the G4's outer appearance, I'd first look at replacing the 120mm fan with a quiet non-thermally controlled fan.

There's also the more extreme option of adding a bottom blowhole, cutting in under the front-most drive mounting plate.

I'd also check that the Mercury's heatsink is on properly, and maybe replace the thermal compound depending on the warranty. Well, I'd do it anyways, but that's just me.

Any fan you're going to be able to fit near the CPU might be too small or too loud to make much difference.

Keep us posted...and photos are always nice. Smile

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You might also consider some

You might also consider some ducting between the CPU heatsink and a fan, or between the mounted heatsink fans and the outside world. This will ensure that there is at least some airflow that is dedicated to cooling the CPU.

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H20?

Have you considered water cooling? It's a bit more expensive than adding fans and such, and you sorta need to know what your doing, but, it could be a lot more effective (and a lot quieter) than air cooling.

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Re: Cooling Digital Audio Power Mac G4? CPU is roasting!

G4 7455B @ 1.467 GHz
OWC Mercury Extreme

I pulled off the two little fans that were on the CPU.

I then screwed on a big 80mm fan to the heatsink. The heatsink seemed to be exactly 80mm wide!

The 80mm fan is just as quiet as the two little (40mm) fans, but moves a *LOT* more air. There is a noticeable breeze coming from the CPU area now.

I clocked the CPU back to 1.467 GHz, closed the case, and let it run Quake3 timedemos all night - an NO lockups!

Here is a picture of the fan on the heatsink/cpu:
http://xenomorph.net/images/mac/owc_14_80mm_med.jpg

This was actually a pretty simple fix. Those original fans are *weak*.

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Wow...I didn't realize the af

Wow...I didn't realize the aftermarket CPU was so tiny.
Good job on the fan swap. Always nice when it's a simple fix.

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