iMac 27-inch, Late 2013 won't boot

[KingCornWallis]

Helping a friend diagnose their iMac; they haven't used it in a while, and don't recall how it got into its current state. Have no idea what OS it is running, likely 10.13-10.15; stock hardware and no history of damage.

What it does:

Upon booting, it attempts to load macOS (black backlit screen with Apple Logo + progress bar) but gets hung up near the very end of the progress bar.

Fixes attempted:

We tried to get into Recovery Mode (Command + R) as well as Internet Recovery Mode (Command + Option + R), both times after loading we just get a black backlit screen. We created a Catalina USB Installer and tried to boot from it, but get the same black backlit screen after loading it. Resetting NVRAM and SMC did not help.


Running Apple Diagnostics (D) came back with no issues. Have no other ideas to attempt for this model besides opening it up (but I am helping remotely).

Any ideas?

 

[Bigwaff]

Any ideas?

Failed backlight. Boot and shine flashlight at display at slight angle. Is an image visible where flashlight shine? With older Mac laptops this was a way to discern whether the backlight has failed. Unknown whether it works as well with the glare on the iMac glass, though.

 

[KingCornWallis]

Failed backlight. Boot and shine flashlight at display at slight angle. Is an image visible where flashlight shine? With older Mac laptops this was a way to discern whether the backlight has failed. Unknown whether it works as well with the glare on the iMac glass, though.

You think the backlight is failed even though we can see the Apple logo and boot options? Is there a difference in the EFI environment vs running an OS/USB image?

 

[Bigwaff]

You think the backlight is failed even though we can see the Apple logo and boot options? Is there a difference in the EFI environment vs running an OS/USB image?

I reread post. Good point. Maybe not display backlight if you see boot screen… and Diagnostics not flag failed GPU or other hardware failure…. is strange indeed. Maybe unplug from power for 10 min and remove RAM and reinsert RAM?

 

[Nguyen Duc Hieu]

I reread post. Good point. Maybe not display backlight if you see boot screen… and Diagnostics not flag failed GPU or other hardware failure…. is strange indeed. Maybe unplug from power for 10 min and remove RAM and reinsert RAM?

Apple Diagnostics only check the GPU at basic level, not on full power (stress test).
A half failing GPU can show the boot screen, go pass ADT, but cannot go pass the driver load to enter Mac OS desktop.
If the reason for failing is overheating, thorough cleaning the machine and re-applying thermal paste on CPU and GPU may help, but the chance is slim.

 

[Eriamjh1138@DAN]

Hold command -V during boot to see the verbose logging window.

 

[KingCornWallis]

Apple Diagnostics only check the GPU at basic level, not on full power (stress test).
A half failing GPU can show the boot screen, go pass ADT, but cannot go pass the driver load to enter Mac OS desktop.
If the reason for failing is overheating, thorough cleaning the machine and re-applying thermal paste on CPU and GPU may help, but the chance is slim.

Interesting, I will try verbose logging and check the back vent for any considerable dust. It's a shame that Mid 2013 was the cutoff for non-server based ASD or I could do that. Opening the iMac is out of the question for the foreseeable future...but I think overheating is likely not the culprit due to how uniform the issue is. Probably the end of the line for this computer, but I will check back later.

 

[Fishrrman]

Fusion drive inside?
If I recall, 2013's had problems with the HDD portion of the fusion drive failing.

Does your friend have an EXTERNAL boot drive?
If not, it might be possible to make one, and get booted from that.

You'll need an external USB3 SSD (doesn't have to be large, even 256gb is enough).
Then boot to INTERNET recovery (command-OPTION-R at boot).
Erase the drive to APFS using disk utility.
Then use the OS installer to install a copy of the OS onto it (accept whatever version internet recovery offers you).

If you can boot from the external drive but NOT from the internal drive... well, it's almost certainly a failed drive inside. Even more likely with a fusion drive.

 

[Nguyen Duc Hieu]

Fusion drive inside?
If I recall, 2013's had problems with the HDD portion of the fusion drive failing.

Does your friend have an EXTERNAL boot drive?
If not, it might be possible to make one, and get booted from that.

You'll need an external USB3 SSD (doesn't have to be large, even 256gb is enough).
Then boot to INTERNET recovery (command-OPTION-R at boot).
Erase the drive to APFS using disk utility.
Then use the OS installer to install a copy of the OS onto it (accept whatever version internet recovery offers you).

If you can boot from the external drive but NOT from the internal drive... well, it's almost certainly a failed drive inside. Even more likely with a fusion drive.

OP already tried booting his iMac with a USB installer of Mac OS Catalina and couldn't get to the installation phase.
And I think USB installer is an external boot drive.