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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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24” iMac 2.8Ghz Intel Core 2 Duo CPU Fan Running At Full Speed

The fan on my 24” iMac starting running at full speed yesterday. I ran Apple Hardware Test and came up with the following error.

4SNS/1/40000001 : TGOD- 1.000

This appears to be an overheating graphics card. I opened the iMac up and blew out all the dust and reassembled. I turned on the computer and before it was fully booted up the fans came on full speed. The computer had been off all night. Is it possible for the graphics card to overheat before the computer is fully booted up from a cold condition?

This is an old computer I use to run two old programs that don’t run on my other system. I am running OSX 10.6. Other than the fans running at full speed the system appears to be running fine. Is this a problem that can be fixed? I read somewhere this is a heat sink problem where the cooling fluid has been lost and replacement parts are not available.

UPDATE: I just downloaded Macs Fan Control and the CPU is running at 3600 rpm. All the temps look fine except the GPU diode. It is at 1 degree centigrade. Is my diode the problem?

Answer this question I have this problem too

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Are you sure you wrote down the error correctly?? I think TGOD- 1.000 should be TGOH- 1.000

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I believe I did. I would have to run Apple Hardware Test again to confirm.

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Dan,

Thank you.

I did not take out the logic board. I just opened the iMac enough to blow out the dust. Except for the GPU diode, all the other temps look fine. The GPU heatsink sits around 42 degrees C when I lower the fan speed to 2,400 rpm from 3,600 rpm. What does the GPU diode do?

I use the computer infrequently so I am wondering if I can continue to use it is this condition if the heat sink is not getting too hot.

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I wanted to add. I just noticed that my screen is at full brightness when I turn on my computer. Once I boot it up I turn the brightness down all the way, but it always returns to full brightness when I reboot the computer. This does not seem like something related to a heatsink problem.

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For good measure why don't you replace the PRAM battery (CR2032 Lithium) As the PRAM holds the settings if the battery is dead that could explain things. Here's the IFIXIT guide: iMac Intel 24" EMC 2111 PRAM Battery Replacement

But that still doesn't explain the error message.

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If you took out the logic board then you might have snagged the sensor cable damaging it or forgetting to connect it. If your sure the connection is sound then it could have failed on the most part I find the GPU needs deeper service. It could be a bad heat sink or need new thermal paste and pads.

As for the software tool you're using I don't have much faith in SMCFanControl as I've seen to many problems with it. I find TG Pro is just a better tool to see whats happening.

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Here's a good IFIXIT guide to help you take out the logic board to gain access to the GPU as we don't have one for your exact model: iMac Intel 24" EMC 2267 Graphics Card Replacement

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Thank you. I could not find that guide when I searched.

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