Are you still able to get into diagnostics from the recovery partition? If you can post the error message here for us to see.
If you can try going in the safe mode to see if something is conflicting. If you can you should be able to still download and install this app: [https://www.tunabellysoftware.com/tgpro/|TG Pro] it will allow you to see the internal thermal sensors and the status of the fans.
* Reference: [https://support.apple.com/en-us/HT201262|Use safe mode to isolate issues with your Mac]
Until we can be sure the issue is also within the logic board I would hate to go down that path yet.
As far as the diagnostic error stating the HD fan was failing thats not uncommon and repairable. I suspect your system shut down due to the high heat not a logic board failure. So for now its important to keep the room the system is in as cool as you can so we can get as much info from the system to diagnose whats really happening here. Once we know we can address what is the needed steps and parts that are needed.
=== Update (08/10/2017) ===
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Stefan Follow this guide: [https://support.apple.com/en-us/HT202731|How to use Apple Diagnostics on your Mac] see if you can get it to run.
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Stefan Follow this guide: [https://support.apple.com/en-us/HT202731|How to use Apple Diagnostics on your Mac] see if you can get it to run.
Here's a bit more explaining things: [https://computers.tutsplus.com/tutorials/finding-hardware-faults-exploring-aht-apple-diagnostics--mac-60456|Finding Hardware Faults: Exploring AHT & Apple Diagnostics]
We really need some onboard diagnostics to see whats up here. Paste the error codes here so we can see.
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=== Update (08/21/2017) ===
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If this is your current error then your hard drive fan unit has failed.
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We don't have a guide specifically for replacing the fan but this guide will get you mostly there: [https://www.ifixit.com/Guide/Installing+iMac+Intel+27-Inch+EMC+2429+Dual+Hard+Drive+Kit/7575|Installing iMac Intel 27" EMC 2429 Dual Hard Drive Kit] Follow the guide to Step31 and carefully remove the logic board fully out. Just behind the logic board is the fan unit which is held by one screen at the bottom:
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[document|3347]
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Here is the part info: Hard Drive Fan - Apple P/N 922-9872
Are you still able to get into diagnostics from the recovery partition? If you can post the error message here for us to see.
If you can try going in the safe mode to see if something is conflicting. If you can you should be able to still download and install this app: [https://www.tunabellysoftware.com/tgpro/|TG Pro] it will allow you to see the internal thermal sensors and the status of the fans.
* Reference: [https://support.apple.com/en-us/HT201262|Use safe mode to isolate issues with your Mac]
Until we can be sure the issue is also within the logic board I would hate to go down that path yet.
As far as the diagnostic error stating the HD fan was failing thats not uncommon and repairable. I suspect your system shut down due to the high heat not a logic board failure. So for now its important to keep the room the system is in as cool as you can so we can get as much info from the system to diagnose whats really happening here. Once we know we can address what is the needed steps and parts that are needed.
+
+
=== Update (08/10/2017) ===
+
+
Stefan Follow this guide: [https://support.apple.com/en-us/HT202731|How to use Apple Diagnostics on your Mac] see if you can get it to run.
+
+
Here's a bit more explaining things: [https://computers.tutsplus.com/tutorials/finding-hardware-faults-exploring-aht-apple-diagnostics--mac-60456|Finding Hardware Faults: Exploring AHT & Apple Diagnostics]
+
+
We really need some onboard diagnostics to see whats up here. Paste the error codes here so we can see.
Are you still able to get into diagnostics from the recovery partition? If you can post the error message here for us to see.
If you can try going in the safe mode to see if something is conflicting. If you can you should be able to still download and install this app: [https://www.tunabellysoftware.com/tgpro/|TG Pro] it will allow you to see the internal thermal sensors and the status of the fans.
* Reference: [https://support.apple.com/en-us/HT201262|Use safe mode to isolate issues with your Mac]
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Until you can be sure the issue is also within the logic board I would hate to go down that path yet.
+
Until we can be sure the issue is also within the logic board I would hate to go down that path yet.
As far as the diagnostic error stating the HD fan was failing thats not uncommon and repairable. I suspect your system shut down due to the high heat not a logic board failure. So for now its important to keep the room the system is in as cool as you can so we can get as much info from the system to diagnose whats really happening here. Once we know we can address what is the needed steps and parts that are needed.
Are you still able to get into diagnostics from the recovery partition? If you can post the error message here for us to see.
If you can try going in the safe mode to see if something is conflicting. If you can you should be able to still download and install this app: [https://www.tunabellysoftware.com/tgpro/|TG Pro] it will allow you to see the internal thermal sensors and the status of the fans.
* Reference: [https://support.apple.com/en-us/HT201262|Use safe mode to isolate issues with your Mac]
Until you can be sure the issue is also within the logic board I would hate to go down that path yet.
As far as the diagnostic error stating the HD fan was failing thats not uncommon and repairable. I suspect your system shut down due to the high heat not a logic board failure. So for now its important to keep the room the system is in as cool as you can so we can get as much info from the system to diagnose whats really happening here. Once we know we can address what is the needed steps and parts that are needed.