iMac 27" 5K (End 2015) Fan speeds up, performance slows down

[soerenwolf]

Hello all,

our normally good working iMac 27” 5K from End 2015 has a defects since some weeks.
The Fan turns up and the performance drops down, so it is not possible to work on the machine.
I tried to install the newest macOS, restart with D = no errors.
TG Pro displayed that the Sensor “Power Supply Secondary Heatsink” = N/A and the fan is turning up high.

Do you have any idea how i can fix this problem?

Thanks so much!

Sören

 

[zeratul75]

I have the same imac and installed that software, just to try.
It is showing that sensor in green, moving between 26 and 27 degree. Did you see that green before problems started?
If so, It sounds like something related to PSU.......

 

[wilberforce]

Suggest switch activity monitor to show All Processes (Alle Prozesse), not My Processes (Meine Prozesse). (View in menu bar.) This will probably show a system process like kernel_task is preempting CPU capacity in response to detected overheating.
This will not solve your problem, but provide some better information. See:

If kernel_task is using a large percentage of your Mac CPU - Apple Support

One of the functions of the kernel task process is to help manage the temperature of your CPU.

support.apple.com

I assume you have tried resetting SMC. May not help, but have to do it regardless.

Reset the SMC of your Mac - Apple Support

The SMC is responsible for managing power on your Mac. Resetting it can resolve certain uncommon issues related to power or thermal management.

support.apple.com