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Model A1419 / EMC 3070 / Mid 2017 / 3.4, 3.5 or 3.8 GHz Core i5 or 4.2 GHz Core i7 Kaby Lake Processor (ID iMac18,3) / Retina 5K display. Refer to the older iMac Intel 27" Retina 5K Display (Late 2014 & 2015) guides as the system is very similar.

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Do I need the OWC inline sensor when I replace the HD?


there have been reports from people upgrading their SATA drives with SSDs not needing the OWC thermal sensor cable you mentioned.

Can anyone confirm this? Is this due to the way the new iMacs are built or rather dependent on the manufacturer of the aftermarket SSD?

Beantwoord! Bekijk het antwoord Dit probleem heb ik ook

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Sorry the world is still round ;-}

Haven't done the new 2017 model, but I can tell you the older 5k still needed it. You really don't want to go cheap here after spending a ton on a new system.

Make sure you review the IFIXIT guide here: iMac Intel 27" Retina 5K Display Replacement on how to remove the display and make sure you use the correct tools! Its very easy to damage display. Here is a good vid by OWC on their teardown: Unboxing and Teardown of the 2017 27" iMac retina 5k

Don't forget you'll void your AppleCare warranty!!

To clarify whats going on here:

Apple uses the internal thermal sensor inside the HDD to manage the systems fan (one of the thermal sensors). Apple contracted with the HD vendors to use custom Apple firmware on the drives so the SATA cable would carry the drives thermal sensor output.

So if you swap out the HDD with a different aftermarket HDD it won't communicate with the system's SMC which controls the fan and interfaces with other system thermal sensors.

As for SSD's they don't get as hot and most don't have an internal thermal sensor, and again the drives don't have the needed firmware to talk to SMC.

This is why you need the OWC sensor. While many people have tried using software to over-ride SMC I don't recommend them. Over time we have learned they are not as effective as the hardware option and many people don't tune it correctly so they damage their systems logic board (which is quite expensive!)

Why do people think they don't need it?

Ah! They put the system back together turn it on and it appears to be running just fine! Well if they ran it a while and monitored the built-in sensors with a good monitoring app like: TG Pro they will see the systems temp ramp up and as the processing load increases the fan will start to go into overdrive. Once it does it tends to stay there (if you disconnect power SMC will reset).

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Is the fan control baked into the firmware, or is it a part of MacOS? Would using Linux solve this?


@naninoni - Your system has a second computer within it! We call it the SMC which manages the needed housekeeping tasks of the system. Here it’s the thermal sensors and controlling the fans to keep things cool!

Now this gets tricky! The SMC does communicate with the OS in this case OS-X or macOS if you have a newer release installed.

MS Windows and Linux (any) don’t have access to the SMC.

Even still SMC will still work, you are just not going to gain access to it or have it tell you when things are not working as they should.

Think of it this way many people built Hackintosh systems (even I did) as Apple was not producing what many needed for a system. Here we are in the inverse! So while running macOS on top was possible, access to the cooling system was likewise limited! I ended up running a dual OS setup with MS Windows just so I could access the hardware.


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Dan Fox zal eeuwig dankbaar zijn.

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