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One way to fix an overheating graphics chip in an iMac
Authored by: bluescreen on Jun 04, '11 08:14:32AM

My iMac killed it's hard drive the first-and half year and then the entire screen/ graphics card and mobo had to be replaced at the three year mark. (luckily I had an extended warranty from Futureshop). It unfortunately began to misbehave again shortly thereafter.

I use mine to run my 54" Bravia HDTV as the extended desktop and use Eyetv and noticed numerous graphics errors lines, failure to refresh etc during overheating bouts. It occurred to me that the upper left hand corner of all iMacs has some sort of an air pocket that traps extreme heat from the graphics card there. (The rear-viewed "right" of the air slot)

To verify this, I inserted a temperature probe in the back top left hand (from the front) side of the back air exhaust slot (right side viewed from rear) around 20 cm (9") from edge. The peak-hold temperature reading there runs around 130F and often (always during malfunction or addressing error graphics lockup-freeze) exceeds 140F.

At first I mistakenly thought forcing cooler air into the bottom might reduce this but it does not. There is an air pocket there caused by the vacuum back-pressure of the internal fans, which are all trying to suck air in through limited air inlets, and blowing out the upper right side of the slot so heat just accumulates there and it just runs away

The correct and ideal simplest way to permanently fix your overheating 24" Imac (iMac6.1 iCore 2 Duo at least, and several other models) requires two fixes.

First download and install smcFanControl 2.2.2. Set it up to provide (still quiet) minimum fan speeds of 2200 rpm for HDD and 2800 rpm for CPU, leave the Optical Drive one at 600 rpm to minimize dust accumulation (or just tweak it up if/when you will be using it much)

Next obtain a 12 vdc enclosed squirrel cage fan like the San Ace B76 you need not buy a new one nor this particular (best) model, but any enclosed suction-blower fan of this type (rather than an open blade straight exhaust) is ideal. It shouldn't cost you more than $5 at a surplus shop. Get and hook it up to an old 9vdc AC adapter (around 10 vdc) to run it cooler and more quietly than full 12v speeds, since it is now sucking heat instead of blowing cold air...

TAPE (with clear boxing tape) It to the rear left corner of the back (3" from the side) so it sucks air out of the hottest point of the back slot and blows it away upwards. The fact that it is an enclosed unit makes it easy to just hold there over the slot with clear boxing tape so it sucks heat out and exhausts upwards

Your Imac will now be fixed - the air slot temps will never exceed 105F again (under heavy graphics use) and your graphics card will stop cooking.

Your iStatNano (degrees C) should read: (at 26C Ambient desktop temperature)

HDD 42
CPU 33
GPU 40
Amb 26
DVD 1 39


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One way to fix an overheating graphics chip in an iMac
Authored by: astonchan on Oct 28, '11 12:33:09PM

I wish I had read this before buying my early 2008 iMac. It failed recently. Pretty much same symptom as described here, boot up for about 5 mins and then keep rebooting. Genius quoted me $400+ replacement of LB. I'd rather throw it away! My 7 year old P4 Dell PC desktop still works fine! If I wanted to, I would be able to boot up even my 486 machine! The iMac is the worst investment I made...

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One way to fix an overheating graphics chip in an iMac
Authored by: rober648 on Oct 12, '12 07:30:24AM
Thanks so much for the great tip! Just installed an enclosed fan in hot pocket area, instantly fixes the problem. Brought my temp from 55 deg C to about 30-32 C even while gaming in windows 7 bootcamp! I've tried everything else to no avail but this works 100% . Thanks again!

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One way to fix an overheating graphics chip in an iMac
Authored by: JLG on Oct 10, '13 12:00:19PM
Outstanding, extremely helpful comment. I used one of these fans:

Slap a velcro ring around the inlet side (I put the "loop" on the fan, and the "hook" on the iMac), put a horizontal strip top & bottom on the iMac itself, and the USB power cord is just the perfect length, even on a 24" iMac.

If the overheating problem has already damaged your GPU (so you still get video artifacts and kernel panics), you can disable Quartz Extreme:

To test whether or not this will actually help you, try booting in safe mode. If it runs perfectly fine that way, then disabling QE will help.

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