Hello, I have a late 2015 27' iMac. i7, 16gb ram, and 1tb SSD. The machine is in a boot loop. I am unable to get into Internet Recovery mode. I took it into the Apple Store and a local repair shop. The Apple genius thought it was a corrupted drive and the repair shop has never seen the issue. I have tried booting from an external SSD and it does the same thing. I am able to boot from the external on all my other machines. I have changed the RAM and it is still doing the same thing. I do not believe it is a bad drive. I have not seen anyone online with the same issue. Please let me know what is going on, I am down bad to get this thing working again.
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iMac diagnosis??
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I do sympathy with your situation, but pessimistically speaking, I can't see how an online community can help with an issue given up by professionals from a repair shop, who apparently had the chance to touch and see the iMac in action.
Things a common user can do with this iMac is changing the RAM or running Apple Diagnosis application, which you have already tried without success.
You might have already tried PRAM reset without success, either.
Other options might have already been tried out by the repair shop, like opening the iMac and test each removable device to detect which one caused the boot-loop.
Or a little more hardcore, taking out the SSD and retrieving the log file inside it to search for the cause of bootloop.
Things a common user can do with this iMac is changing the RAM or running Apple Diagnosis application, which you have already tried without success.
You might have already tried PRAM reset without success, either.
Other options might have already been tried out by the repair shop, like opening the iMac and test each removable device to detect which one caused the boot-loop.
Or a little more hardcore, taking out the SSD and retrieving the log file inside it to search for the cause of bootloop.
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Shut down the computer. Connect your keyboard directly to one of the USB ports on your iMac.
If you have a way to connect your iMac by Ethernet cable to the Internet that will save you a step entering your wi-fi password when you boot into Recovery Mode.
Reboot the computer and hold down either Option-Command-R or Option-Shift-Command-R which in my experience, having the same computer as you, the later is the only way to get into Recovery Mode because of the Firmware likely being stuck at 170.0.0.0.0. You can check which firmware version you have in System Information.
Details about this problem can be found here: https://eclecticlight.co/2020/03/25/do-you-have-an-imac-retina-5k-27-inch-late-2015-imac171/
Once you're booted into Recovery Mode run Disk Utility>First Aid. Reboot the computer and see if the problem's been fixed.
If not, boot back into Recovery Mode and reinstall the OS. Bear in mind that it will install the original OS that came with your iMac if you use Option-Shift-Command-R.
If you were able to boot into Recovery Mode using Option-Command-R then you'll be installing the latest version of OS Monterey.
If you have a way to connect your iMac by Ethernet cable to the Internet that will save you a step entering your wi-fi password when you boot into Recovery Mode.
Reboot the computer and hold down either Option-Command-R or Option-Shift-Command-R which in my experience, having the same computer as you, the later is the only way to get into Recovery Mode because of the Firmware likely being stuck at 170.0.0.0.0. You can check which firmware version you have in System Information.
Details about this problem can be found here: https://eclecticlight.co/2020/03/25/do-you-have-an-imac-retina-5k-27-inch-late-2015-imac171/
Once you're booted into Recovery Mode run Disk Utility>First Aid. Reboot the computer and see if the problem's been fixed.
If not, boot back into Recovery Mode and reinstall the OS. Bear in mind that it will install the original OS that came with your iMac if you use Option-Shift-Command-R.
If you were able to boot into Recovery Mode using Option-Command-R then you'll be installing the latest version of OS Monterey.
