fyi I can share my experience with this machine and this same problem.

until recently I had this model iMac 24" 2.33GHz with nVidia GeForce 7600GT graphics card. it had intermittent heat-caused graphics problems, specifically:

a) occasionally, random horizontal lines on the display or within a window would become corrupted, or

b) when running 3D intensive apps, there would be massive graphics corruption over the whole screen, eventually leading to a severe random crash and lockup of the machine.

the problems would only occur when the machine was running hot. Problem a) could occur no matter what application was running, even just within the Finder. usually just single horizontal line would be corrupted.

since I had a month left in my 3 yr AppleCare warranty I brought it into the AppleStore. they confirmed it was a hardware problem and replaced the logic board and CPU fan which seemed to be running a bit slow. we reproduced the problem in-store by running a lot of graphic-intensive apps, a bunch of flash-heavy websites, and even partially blocking some of the airflow vents on the machine.

after replacing the logic board and fan, they still said they weren't satisfied the problem was solved and ordered a replacement graphics card. (this matches what I have read on various internet forums - that this problem is due to the graphics card in this model iMac)

Unfortunately they had problems sourcing a replacement graphics card and after many weeks of waiting they offered to either continue waiting for the replacement (unknown ETA), or replace my 3yr old 24" iMac with a brand new 27" 3.06GHz C2D machine. you can guess which option I chose :) AppleCare FTW

anyhow just fyi, this model does appear to suffer graphics card problems under heat. if your warranty has already expired, then yes smcFanControl seems to be one way you can at least mask the problem. Otherwise, perhaps try replacing the graphics card. I've not looked at the graphics card myself, but apparently they have a MXM (Mobile PCI express Module) interface. good luck.

So will replacing the logic board/graphics card permanently fix this issue? Did they redesign the LB? Or if I have the GB replace, will I run into the same issues as before?

thanks

Phil

There are issues with the gpu in that model. It will overheat and burn off or cause other parts to decay fast like capacitors. The caps go as soon as you start seeing noise in the screen (ghosting, static in picture, hissing sound from the system that changes with picture movements like a window or mouse cursor) A replacement card is the only option if you do not know how to repair smd devices (surface mount devices on the board) The caps are the silver aluminum things. My guess is a design flaw in the heat sink or thermal compound.

I also used smcFanControl and it fixed my same problem with the heat-caused graphics problems. I also placed smcFanControl on my Mac Mini that's in a little shed that the sun beats on in the summer, It fixed my lockup problem on the Mini

You might want to do a little cleaning, just recently, my ATI Radeon X1900 XTX in my pc was overheating, and acting up. I dissasembled the heatsink for the card, and cleaned the dust out of it (and there was quite alot of it, since i've had it for 2 years) and after that, removed the heatsink entireley to re-apply the thermal paste(i used artcic silver 5, the best stuff around) and not the card runs like new, the graphics card heatsink should be removable, and if your warrenty is expired, apple can't really help, so if you want to take apart your iMac, try cleaning out the dust, from all of the heatsinks (even the cpu) and then remove them and re-apply a thin layer of artic silver 5 (a tube costs about $10 at radioshack) and then put it back together.

Good Luck,

Chris

I had multiple problems with the iMac (late 2006 Intel Core 2 Duo 24")after a few years of use. The computer was running extremely slow even after all manner of fixes including bigger HD, resets of everything, Drive Genius fixes, etc. Then it started freezing in mid opening of applications with a distorted image of a half opened application plus lines through the screen. It became unusable with no fixes from Apple Store recommended other than possible logic board.

I opened it up again and thoroughly cleaned with compressed duster - fan blades, ducts, conductor and cooling fins. In addition the GPU was blown out as well as possible. Finally the gap in the duct between the CPU cooling fan outlet and the copper heat conductor was sealed with aluminum tape and a bit of tape was used around the openings in GPU to keep air flowing through it. (Note the iMac 24 MA 456LL/A that I have is quite easy to open. You do not have to use the credit car to pry back the levers found on some of the other iMacs.)

The unit was reassembled and smcFanControl was downloaded and installed. Before installation the GPU was running over 105˚F with no heavy use. After smcFancontrol even with heavy use the GPU rarely went over 98˚. The problems have disappeared and all seems well. The cost of repairs was $4.50 for a roll of tape of which I used about 6".

You do know that when you delete that file desktop composition is disabled. (quartz) It is probably the cause anyway though.

I've been having the same problems with my Imac 2006 with the NVIDIA GeForce 7300 GT card. I installed SMC Fan Control and it helped, I cleaned the fans 6 months ago.

Anyway I took the computer apart again and cleaned it throughly. When I took apart the fan on the left side, unsnapping the duct cover, there was a large amount of dust on the radiator fins of the graphics cooling heat sink. I estimate it was plugged about to 50%. I vacuumed it out and cleaned the fans, it seems to run cooler now as more air flow gets across the heat sink....

There was also a bit of dust on the air intake on the bottom of the computer.

It's worth a try.

Ed

Hello everyone.

Same story --- my 2.16GHz 2006 white iMac started to show all kinds of ill behavior (graphics noise and strips, completely garbled graphics, and system-hangs) all related to heating.

Following the tip I found here -- I installed smcFanControl, and it improved things for a while. However, it deteriorates over time, and now I can't use the machine unless the air conditioning is turned on in the room.

It starts to show signs of malfunction as soon as smcFanControl reports anything over 31celsius (round 90F).

Our area is very dusty, and I'm quite sure some cleaning can improve things again. However, I'm quite sure it can't SOLVE things.

In addition --- the internal superDrive stopped being able to eject discs, which again is something reported here. Up until now, I couldn't find reasonably priced internal replacement drive -- but now I saw some ~$90 used drives here.

I guess it is time to open the machine... My questions are:

1. Are there any detailed tutorials for replacing the GPU card?

2. Did anyone actually replaced his GPU, and (the iMac) lives to tell the story?

3. Where and How can one purchase the right GPU card for this rather old machine?

4. Are there any specific recommendations here for replacing the internal HardDrive (upgrade for bigger storage) to something which also RUNS COOLER ?

I never took apart this iMac, and the tutorials for replacing the optical drive don't exactly encourage me to try. Prying open the case seems a little dangerous - I could break some of the levers, or something).

I dealt with lot's of electronics in the past, but I remember macs to be a delight to dismantle (orignal Macs, Mac II series, Quadras, PowerMacs, PowerBooks G3 G4 and G5 Towers, Intel Mac Pro's and many others --- however, this seems to be very different, and very risky ---

I need some encouraging here :)

Thanks!

Hi. Finally I found the solution.

During last year my imac24" worked so hot. It was so noisy.

Now it's over.

Here is what I've done: one more fix