View source for IMac slim fan runs constantly and processor is slow

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[[Image:SSDFanCtrl.jpg|300px|thumb|right|SsdFanCtrl provided a temporary fix, Recovery mode was the cure!]]
Hardware: Apple iMac with the slim body, the Retina version.  

One day I noticed the cooling fan running constantly (very noisy!) and running any application was hopelessly slow as if the processor was running at about 10% efficiency.

After lots of Googling, the favoured solution seemed to be to reset the SMC [''System Management Controller''] or to reset the PRAM.   None of these made any difference, even after trying multiple times, just incase it didn't work first time.

I was pretty confident that this was not a Virus problem and started to worry that I might have caused some damage when I knocked it over a few weeks before.  I did think I might have dislodged a heat sink which could possible have caused the problem.  However, dismantling these version of iMac is impossible so I thought I was stuck with this problem.

I found a temporary solution for the fan noise by using a utility to slow the fan down, see end of article.  However, the system was still running extremely slowly, almost unusable.

===The solution - just re-boot to Recovery Mode!===
As a last resort, I decided I would have a go at reverting the operating system to a previous version by using my Time Machine backup.

I Put the system into '''''Recovery Mode''''' in order to do this [Shutdown the system, then Cmd + R + Power on].  When the system came back on I realised the fan had stopped running at full speed.  At this point I did not want to proceed with the recovery mode as it looked as though this action had cured the problem, so I forced a shut-down by holding the rear power switch for 5 seconds.  I then powered on normally and the system works perfectly well and there is no more fan noise.   Brilliant fix!

===Purple tinted screen problem===
Almost immediately following this issue, I had a problem with the iMac booting up with a pure white apple icon in the middle, which almost immediately turned purple-ish as the boot proceeded.  Once the system was up and running the screen had lost its lovely brilliant white effect.  However much tinkering with white-point on the Display utility, I could not get a pure white screen, it always had a purple hue.

The screen tint was cured by booting up in Safe Mode [Shut down, hold down shift and power on].  After Shutting down and rebooting in normal mode [just power on], the white screen returned to normal.  I wonder if the mutitude of restarts, force quites etc had somehow created a confused config which Safe Mode managed to cure.

===See also===

* [http://exirion.net/ssdfanctrl/ SSD Fan Control - use to slow down noisy fans on Apple iMacs]]
* Reset SMC: Shutown. Shift + Ctrl + Option + Power on - release keys and press power switch again
* Reset PRAM: Shutdown. Command + Alt + P +R and power on
* Enter Recovery Mode: Shutdown. Cmd + R + Power on
 
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