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2017 iMac 27" NVMe swap: slow OS, kernal-task taking CPU, temp sensor?

spencersmitty

spencersmitty

macrumors newbie
Original poster
Oct 9, 2021
25
3
hi,

I recently swapped out my (2TB) dual fusion drive setup on my 2017 iMac 27", to a singular 2TB Samsung 970 Evo Plus NVMe with the Sintech adapter. Alongside the SSD swap, I also installed 32GB of Crucial memory, coming from the stock 8GB apple memory. Before I sealed the screen back up, I removed the SATA cable that connects to the Seagate drive as I wasn't putting another SSD back in its place like many youtube videos show (why would I need two drives?).

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well I was sorta expecting it after stories I heard, and it happened; my fans went full blast since the 'temperature sensor' firmware from the seagate drive is no longer present inside the iMac (i'm use the Mac Fan Control app as a temporary fix for the time being, if anyone knows the correct way of remedying this, lemme know). Ive heard the OWC adapter is sort of controversial of what it actually achieves so I didn't bother getting it.

Alongside the fans going full blast was another change, and that was this subtle, high-pitched repeating chirping noise coming from what it seemed like the bottom of the iMac near the speakers. I noticed the sound would change when I scroll on a webpage, or mostly change my brightness up and down. After a bit of research I come to find out this is called 'coil whine' and it actually may be sourced at one of the power supply coils if I understand correctly? I have purchased a replacement power supply to swap out in hopes to remove the chirping but my hopes are preeetty low, lol.



Anyways, sorry for the long intro to my main issue here, and that's the speed of the new 2TB NVMe.

I installed Mojave and ran updates after, but noticed that the OS was super sluggish: booting the computer takes longer than my fusion drive setup at about a minute-ish, waiting for apps or any processes to open takes like 10-15 seconds, and when I noticed the dock's magnification effect looked like it was 15fps I realized something was off. The whole computer feels like a dated Mac with a HDD inside of it. after googling my symptoms, people said to make sure your default drive was set to the new SSD, and it is. I have tried enabling TRIM inside of Terminal, but it didn't automatically reboot for me so I don't think it was able to activate; to be honest I'm a little knowledge-lacking of the correct way to configure a NVMe on after installation, hence why I'm here. Aside that Im getting a little exhausted of trying to dig up what's wrong o_O, but trying to stay optimistic...

(UPDATE: enabled TRIM, didn't change)

Screen Shot 2021-10-09 at 13.04.33.png

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(UPDATE: switched out ram for the old OEM Apple 8GB, no change)

so yea, slow OS after installing an NVMe. could it be the ram? the TRIM or any other setup steps? the power supply not preforming correctly? (ehh), or something else.

I'm stuck here now so any useful help is appreciated.

thank you
 
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Hey

The issues you're experiencing here -- I can relate them to times where the iMac is not getting a connection to the LCD.
I am wondering if there is a chance that there is not a full connection from the LCD to the logicboard, and this is what is causing the fan ramp + slow OS, as these iMacs will appear sluggish and very laggy, low frames if it's not properly detecting all pins are connected from the LCD. The high-pitched noises I am hearing from that video sound like the fan too.

For your scenario - the OWC adapter is not necessary, and is only ever required when installing a non-OEM HDD.
If possible - does Mac Fan Control show a sensor reading for the LCD? If not, this would be the main reason for most/all of your issues you're experiencing.
 
I think its recognizing it?

and, I thought it was the fan at first hearing.. but I think it might be something else since it changes with scrolling of the mouse, brightness, etc :/
 

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Yeah, LCD sensor is being read. There is still the slight possibility that re-seating the LCD cable will fix the sluggish issue.
I do notice there is a lack of PSU temp sensor on that list -- so it is possible that PSU could be the culprit on the fan ramping issue.
 
well... anything I can do within the OS first before slicing this thing apart again would be preferred; i'm not sure if the LCD cable would cause the whole computer to throttle down like this. Fans is due to the lack of thermal sensor software within the HDD.

maybe more ideas/tips out there why OS/boot is sluggish?
 
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okay, did more poking around and found ‘kernel-task’ is taking 400-500% of the CPU usage. upon some research through threads, i think it’s due to the OS looking for the temperature sensor?

i just don’t understand how that’s possible since the 2017 imac uses S.M.A.R.T to monitor the temps and any sensors like the aftermarket OWC one is not even needed.

my guess is SOME sensor inside the imac is not being read or something.. I dunno. i’m pretty exhausted from digging through forums and finding… nothing. i feel like so close to an answer.

please someone chip in if you know anything
 
Like I said - I'm pretty sure there is meant to be a PSU temperature sensor. This could be what is causing the fan to ramp.

As I said in my first post -- the OWC adapter is not necessary at all. There is no issue of a missing temperature sensor due to your SSD or lack of SATA storage.
 
How about trying to install windows 10 and check how it works there? On windows you should also be able to use samsung magician to check the firmware version (not sure if it can detect the ssd when inside the mac).
 
970 Evo Plus is a great drive for Windows but is not really good for macOS (even with latest firmware). You’d be better off with WD Black SN750, or something with Phison or SiliconMotion controller (some high-end Gen 3 ADATA models, for example, or Kingston KC2000). OS booting speed will be well improved, at least.

Adapter is passive, it simply connects lines from drive to Apple’s interface, so it does not affect speed.
 
gian8989 said:
How about trying to install windows 10 and check how it works there? On windows you should also be able to use samsung magician to check the firmware version (not sure if it can detect the ssd when inside the mac).
Click to expand...
i was planning to install windows to play diablo. i was able to update the ssd with a bootable usb through holding option on startup :)

i will see how it performs there.
 
JonathanX64 said:
970 Evo Plus is a great drive for Windows but is not really good for macOS (even with latest firmware). You’d be better off with WD Black SN750, or something with Phison or SiliconMotion controller (some high-end Gen 3 ADATA models, for example, or Kingston KC2000). OS booting speed will be well improved, at least.

Adapter is passive, it simply connects lines from drive to Apple’s interface, so it does not affect speed.
Click to expand...
good to know, thanks for the suggestions!
 
TwoH said:
Like I said - I'm pretty sure there is meant to be a PSU temperature sensor. This could be what is causing the fan to ramp.

As I said in my first post -- the OWC adapter is not necessary at all. There is no issue of a missing temperature sensor due to your SSD or lack of SATA storage.
Click to expand...
ok, my apologies man.. i will dig around some more for that PSU sensor. maybe there’s a better program that could show all the sensors inside the mac?

i just remember seating all my connectors inside very well: i didn’t want to re-open it up because i half pressed a connector down or something.
 
spencersmitty said:
okay, did more poking around and found ‘kernel-task’ is taking 400-500% of the CPU usage. upon some research through threads, i think it’s due to the OS looking for the temperature sensor?
Click to expand...
Yes, high kernel_task is used by the system as a dummy process when it thinks it is overheating, to effectively deny CPU usage to real processes

btw, the max fan rpm should be 2700 rpm for this iMac, not 3600. Possibly something wrong with the fan control system? Unfortunately I have see several threads with this (or a similar) issue, with no reported solutions.
 
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wilberforce said:
Yes, high kernel_task is used by the system as a dummy process when it thinks it is overheating, to effectively deny CPU usage to real processes

btw, the max fan rpm should be 2700 rpm for this iMac, not 3600. Possibly something wrong with the fan control system.
Click to expand...
yes, its… yea. I just need to figure out which component inside the iMac is causing the false temp signal: PSU, Lack of HDD, the new NVMe... ?

don't want to, but ill probably have to start unplugging connectors inside and making sure they are seated correctly (which I'm 90% certain they are) and see if the Mac calms down. there is so little information about this scenario online it baffles me

as for the fans.. no clue.
 
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hey, back again :/

mac runs great but i’m getting random restarts into kernel panics due to the common “nvme fatal error” log.

going to try to reinstall mojave today and see if it helps. 😖
 
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HI There -

Guess misery loves company lol. I also have an iMAC 13,2 I just upgraded to a OWC 2TB SSD and have a Racer X Fan tearing up the track. I left the old SATA Connected but planned to replace that as well with an SSD. Did you ever resolve your issue. Any insights would be welcomed.
 
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