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Old Dec 31, 2010, 06:10 AM   #1
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Join Date: Dec 2010
New project... getting real on imac g5's cooling

Good day Gentlemen,

First, I'm Ricardo, a mac user in the science/engineering field since 2001. I've gone through almost all the models after my first Performa 630CD that my father gave me back when I was at high school. I've suffered what most of you have with those unexplainable lousy decisions from apple on the construction of their computers, but also I'm faithful to the brand.

I've got one of those ****** iMac G5 with bad capacitors and high temperature issues. I'm a good engineer and work at a top notch research facility with every equipment you could ever dream of...

This computers was on my parent's place since 2004 and only a year ago it started failing, which turned out to be bad caps... I just bought them a new intel mac mini with a 24" dell display... good for them!

Last week though, I decided to do something about that iMac, first thinking about giving it away to my maid's son.

1- I ordered new ECR new caps, the entire set for the motherboard (didn't touch the PSU as the symptoms had nothing to do with power, only graphic glitches).
2- I replaced the 25 caps and the computer started fine, I did a fresh install of Tiger...


3- The fans began to spin like crazy and lines began appearing on the screen, and lately, Kernel Panics after 5 minutes on the desktop... as bad as that!
4- The problem is definitely temperature, the CPU is running very cool (never above 50 deg C), I replaced the grease for non-conductive Cooler Master TF400 (I work with cryogenic equipment and high level cooling, and after reading its specs, I preferred it over Arctic Silver 5). However, I couldn't do anything about the thermal pad on the ATI chip, which is the one that gets hotter, even if I touch the heatsink, right on top of the ati chip, the pattern of lines changes...
5- I saw some rust on the G5 heatpipes' welding, which led me to believe that they might have broken and there's no liquid inside anymore

Since I couldn't give away a computer in such conditions, and the hours I spend replacing the caps... and of course the hurt pride... I decided to roll up my sleeves and get serious about this.

This is my plan:

Get a new fan/heatsinks for both the VGA chip, and the CPU, while improving the air flow. The steps to do this would be:

1- Open 2 holes on the back of the imac, one for each fan's intake.
2- Divide the ductwork between the cpu and the ati chip, so the hot air from the ati chip is discharged through the upper hole on the mac mini, and the cpu's hot air through the bottom existing grid. If necessary, I'd build new aluminum ducts and remove all the existing elements that add unnecessary resistance to the air flow.
3- Although I will use low profiles fans (CPU's is only 36mm tall), it is more than likely that I'll have to drill a hole the size of the fan on the imac's back, to finish it properly, I'd manufacture an aluminum grid on our CNC machines, and then finish it with fine sandblasting.

But, as usual, a lot of questions are popping up in my mind, and I was hoping to get some advice from you guys. Just be open, if this doesn't get fixed, it's OK, also this is not for apple's tech service... it's this or nothing...


1- What are the thermal specs for the G5 CPU? I'm planning to get a Thermaltake SlimX3 fan, which is the lowest profile fan for Core 2 Duo and i5 processors in the market. It works on heatpipes and a solid block of aluminum, that I could drill to match the G5's logic board holes. It's only 36 mm tall.

Thermaltake SlimX3

2- I'm really disappointed at the ATI chip, it's performance is really bad compared to the temperature it reaches... anyhow, I'm installing a fan/heatsink here too. I thought this Zalman would work great, and it has lot of holes to fit the holes on the logic board.

Zalman VF-900

I really believe these components, designed for last generation chips surpass the thermal requirements of the imac... just need to hear some encouraging comments to go ahead with the project.



P.S.: By mistake, I posted this as a reply on another thread... sorry about that....
ricardoph is offline   0 Reply With Quote
Old Dec 31, 2010, 07:03 AM   #2
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Join Date: Feb 2010
Location: Where Judas lost it's boots.
Sounds like an overkill to me. Most likely the ati chip needs a reflow since those imacs are very hot machines and they had problems with the ati chip overheating. And the heat will ruin those brand new caps.

Since it looks like the heat pipes are ruined. you will have to be very creative with the heat-sink placement. The zalman one is really low profile (I have one) the thermaltake I don't really know.
Now the real pain will be mounting the new heat-sinks it should be a good project to do.

Some people already made holes for extra fans. but it looks ugly as hell

If you go forward good luck with your project
Lenovo ThinkPad + Nexus 7 (2nd Gen)
blackburn is offline   0 Reply With Quote
Old Dec 31, 2010, 11:35 AM   #3
macrumors 6502
Join Date: Aug 2006
Location: Boondocks
Try this link here:

Spend some time on this page below. Helped me a lot with my G4 project in the past:


and here are some issues you may already know regarding the cheap caps, Apple has used in your model. Its a good read anyways..


some on fans..


good luck for your project and a happy new year 2011 !!
MacBook Pro 17' i7 2010, Samsung Evo 1TB,
27' ACD; TC, iPad 3, iPhone 6, iPod touch 1.gen, NAS: 214play (2x4TB),
AlexMaximus is offline   0 Reply With Quote

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