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Model A1225 / Early 2009 / 2.66, 2.93, or 3.06 GHz Core 2 Duo processor

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Fan at max speed, vertical lines, burning smell

My Early 2009 iMac (3.06 GHz Intel Core 2 Duo) has recently had an extremely loud fan. Using a fan utility I can see that its the CPU fan that is running at max. After a period of time, the screen will go to vertical lines and fan is off. I'm wondering what makes the fan run high in the first place- and why does it shutoff eventually?

How can I diagnose? I'm unable to boot into diagnostic mode, that appears to be something added in later models.

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try this, Unplug the power from the back of the computer wait a couple of minutes and then plug it back in and restart the computer

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My best guess wold be that the CPU is hitting its T-Junction and shutting off. Before it shuts off, can you see what temperature it registers at before it shuts down? It is also likely the Graphics Card is hitting its thermal limit, hence the vertical lines. Try using a program like AIDA64 to monitor theses temps. If its anything above 80C after startup, you have an issue. Good luck!

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Temperatures and fan speeds start out what I believe is normal and start ratcheting up over time, I'll try this tool and see if I can see what's going first. I wondering if dust build up could cause this heat build up?

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@bclingan Yes! Dust, old thermal compound, any number of things could cause this. What you just described was exactly what I suspected. Check GPU temps too and report back. Good luck again!

EDIT: Also, be very, very careful. That burning smell is bad, keep the device off whenever possible until you fix it. Prolonged extreme heat is very damaging to components.

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I blew a ton of dust out! Sadly I didn't note all the temps before I started, but I believe they are lower than what I recall. Does anyone know if these are in the correct range?

Ambient = 16

CPU Diode = 31

CPU Heatsink = 28

CPU Proximity = 34

GPU Diode = 90

GPU Heatsink = 84

GPU Proximity = 79

HDD Proximity = 29

LCD Proximity = 27

MCP Proximity = 49

MLB Proximity = 34

Northbridge Diode = 60

Northbridge Heatsink = 56

Optical Drive = 28

Power Supply Proximity = 35

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Fan climbs and maxes out still after being powered on for several minutes.. wondering what to check next.. heatsink? thermal paste?

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@bclingan From what you described, I'm willing to say all of those temps are fairly normal, except for the GPU. My R9 380x is known for being hot, it never passes 80C. I'd replace the thermal paste on the GPU, also the CPU while you were at it. There is bound to be a lot more dust hiding as well. I appreciate your response. Hope that helps!

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Bob Clingan will be eternally grateful.
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