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Model A1419 / EMC 2806 / Late 2014 or Mid 2015. 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (ID iMac15,1); EMC 2834 late 2015 / 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (iMac17,1) All with Retina 5K displays

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kernel_task at 240, fan spins normally

Hi all. So I got this iMac 27” Late 2015 with a mechanical HD. It was behaving normally. I left it there sitting for a couple of months. Lately I replaced the HD with an SSD. I noticed it was very slow. Installing Monterey took forever. Monitor activity shows kernel_task at 240/250, but fan spins normally. What I did so far:

  • Cleaned all the dust inside of the fan. There wasn’t much anyway
  • Replaced the memories with timetec ones as they’re certified
  • Replaced the ssd with a brand new samsung one
  • Removed the logic board and got rid of the 32 GB blade ssd
  • Replaced the PSU board with a known good one as I’ve read it carries thermal sensors which could cause the problem
  • Replaced the fan with a known good one
  • Diagnostic (cmd-d on startup) shows nothing
  • Safe-mode doesn’t change things

There are no apps running, no third party software. Monterey is clean install, including latest update (which also took forever).

Apart from speakers, I can only try to replace the sata cable, the pram battery and the wifi card. If that makes any sense.

Any suggestion would be appreciated.

Thanks everyone.

Answered! View the answer I have this problem too

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I’m suspecting SMC is in CPU safe mode where the fan is ramped up and the CPU’s clocking is lowered.

So why is SMC thinking things are bad? You’ll need to run the onboard diagnostics to figure that out. While not 100% it’s the first thing I would do.

Restart your system and press the D key to enter. Let us know what you discovered.

Reference: Mac startup key combinations

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18 Comments:

Hi Dan. Thanks for jumping in.

I wrote in the title that the fan spins normally, it’s not screaming.

I also wrote among the things I tried there’s the onboard diagnostic, which found everything ok. That’s why I’m so puzzled.

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@mafomo - I would double check, sometimes the fan doesn’t ramp,up. If Diags didn’t show any failures then I think you need to install a good thermal monitoring app like TG Pro as that only leave the heat sink as the problem.

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Hi again. Test repeated twice. Always the same

No issues found, reference code ADP000

I’ll install TG Pro and will post results

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Fan at 1200 rpm

All temperatures between 31 and 41ºC

41ºC lcd backlight controller proximity, amd radeon r9 m390 core.

Cpu all values between 33 and 36ºC

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@mafomo - Really need to see the snapshot as it's a bit more than just reading the temps of the major chips.

Also did you just swap out the HDD for the SSD or do something different?

Besides being a hardware level issue this could be a software one! Setup a bootable external drive with the same version of macOS your system is running see if that makes a difference booting up under it.

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