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Model A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, or 3.06 GHz Core 2 Duo processor

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Overheating , fans running high , shuts screen off after 15 mins

I have a mid 2007 imac 24" intel duo core

My problem is all of a sudden it started the fans running high, runs for about 15 minutes and then the screen shuts off. The fourth led goes out and that is it, everything stays on and the fans are still on high.

Also I took it apart and blew out the fans and dust ( it wasn't that bad, but I could not get at the fan behind the main board yet )

When it is running nothing feels hot on the back or front , but I did notice that the upper left back corner was extremely hot and now it is not. Could a faulty sensor be the problem?

Here is a read out of my settings


HD. 38 degrees Celsius

CPU. 30

Airport card. 55

Ambient. 22

GPU. 110

GPU diode. 126

GPU heatsink. 126

HD bay. 41


Optical drive 699 rpm

Hard drive 1291 rpm

CPU fan 3309 rpm

Also it does not need to be unplugged to restart.

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problem was never resolved


Hello Darren.

I'm having literally the exact same problem with my iMac. Did you ever remove the graphics card and see if there was any physical damage done to the circuit? I think it could be a blown up capacitor or something . . . .


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After it has cooled down:

Start up from your system installation disk or secondary disk while holding down the "D" key until the AHT (Apple Hardware Test) starts up. Run it and let us know of any codes it gives you.

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Tried a third test and another error code came up

1st. Error 4SNS/1/40000000:TGOH-102.500

2nd error 4SNS/1/40000000:TGOH-112.375

3rd error 4SNS/1/40000000:TGOH-120.625


LED #4

Indicates that the computer and the LCD display panel are communicating. This LED will be ON (turn on and remain on) when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.


First make sure you have a backup of your User folder on an external drive.

This sounds like a Hard Drive error. See if you can start up from your system installation disk and run Disk Utilities. Have you ever changed the hard drive?


Yes the hard drive was replaced with a 1 terrabyte one about 3 months ago. There were more errors showing up every time I ran the test, the display went out about 20 or so minutes so I could not do a I depth test like the choice I had when I first ran the test. Would you like the other error codes ?


The other codes that came up are 4th error code 4SNS/1/40000000:TGOP-108.000 5th error code 4SNS/1/40000000:TGOP-114.000 6th error code 4SNS/1/40000000:TGOP-121.000


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Darren - Did you jumper the HD SATA I/O speed down?

Newer drives are often SATA II or SATA III while your system's interface is SATA I or SATA II (depending on your firmware) which is likely the root problem here.

You see, your system is constantly trying to read/write to the drive but is having a very hard time accessing the HD which is why your CPU is over heating.

You could try accessing Activity Monitor to see what processes are running and what is using the most CPU. I would also run a temperature monitoring app like Temperature Gage from the App Store to see what is over heating. This app does logging so it can catch the temp just be for the system shuts down on you.

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Darren, the only way to permanently fix the symptom is replacing the video card. I can confirm this because I just replaced my video card. I do not have GPU overheating issue any more. I have been watching full HD online movies for several days (stress test for the card), the overheating issue is gone. The highest GPU die temperature is 61C, normally it is around 50C without online videos. Before replacing the card, my old card can easily reach 128C in completely idle. I have been trying many ways to fix the old one, however none of them worked. Ways I have tried:

- replacing GPU heat sink compound

- adding an extra heat sink to GPU

- removing air wall under GPU

- reflowing GPU (the GPU died after this, don't try)

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How did you replace the GPU card as in my iMac it is a single circuit board for CPU and GPU. Also, dod you replace the cooling pipes as well? or reapply the same using the heat sink compound?


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I am having the exact same issue that Darren has, and I just bought a new GPU, and it didn't solve the problem. It's almost indisputably a logic board problem, but the logic board looks beautiful under a microscope. Can't find anything wrong with it physically.

I'll keep looking. If anything comes up, I will post it here.

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I can confirm Tommyjames337. I have exactly the same problem. Had the GPU replaced and the problem is still there. The hard drive was replaced some time ago, and the problem didn't start then. So there must be another issue.

Unfortunately the imac doesn't run long enough to finish AHT.

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Did you replace the heat sink with the GPU? If not you could have a bad heat sink. Use a magnifier to look for a pin hole on the copper tube. The coolant may have leaked out.


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