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Model A1418 / Late 2012 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor

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FAN is running at high speed when off or in sleep mode.

A problem with a 2012 21,5” iMac. If it’s off or in sleep mode the fan is spinning at high speed. iMac is working quite well, even the fan doesn't behave strange as along as the computer is running. But it becomes strange when I shut down (or sleep mode) the Mac, because when the machine is OFF, the fan runs riot.

The fan stops only in this two cases:

  1. I physically disconnect the power cable. After doing so, I can wait as long as I want (I tried 8 hours during night). In the very moment when I reconnect the power supply, the fan instantly starts running at top speed and won't stop again (I lost patience after 20 minutes and then I pulled out the plug again).
  2. I press the on/off-button on the back of the lower left corner of the Mac. In this case the fan stops on the spot and the startup-procedure beginns and everything is fine.

Tried all the SMC and NVRAM resets and disconnected the harddrive when it was open, but nothing helps.

Does anyone know what this problem is? Maybe a faulty sensor on the logicboard?


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Did you change the hard drive?

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Yes. I disconnected the SATA and turned it on. The fan blowed immediately 100% when the plug was attached.

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The systems fan appears to be working correctly. Can you clarify what you are trying to do here are when you suspect the problem is happening.

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Yes unplugged the hard drive and installed a new one, still same problem.

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I would install TG Pro and post a snapshot of it here. Who's drive did you install?

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Lets see if we can narrow down which sensor is causing the problem. Install TG Pro and post a snapshot of the main window showing all of the sensors so we can see whats up Adding images to an existing question

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Yes here it is.

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Hello

I have answered this question many times

First install SMC fan control of similar program. Check that the program control the fan speed. If it can not control the fan then the problem is with the fet driver in that it is connected by failure to the s5 rail which is live all the time when machine is off. If you can control it the problem in my experience is the SMC chip which has failed. Change it.

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Machiel van der Plas will be eternally grateful.
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