2020 iMac boot loop problem

[Schnauzer World]

During upgrade to 14.7, got black screen, then screen got slightly brighter with bootup tone. After that just loops over and over, never fully booting.

Things I've tried.

Will not boot into recovery.

Will not run diagnostics.

Reset NVRAM and SMC twice, making sure hearing the reset tone twice.

I have three different bootable macos on flash drives Monterey, Sonoma, Ventura, nothing except on one occasion Monterey almost booted, entered wifi password, selected Monterey, then back to the loop.

Sounds like maybe bad SSD?

Any other ideas.

Specs: Original owner - four years old.

2020 iMac , 27 - inch: 3.8 Ghz i7, 64 GB 2667, Radeon Pro 5700 XT 16GB, 1 TB SSD

 

[Fishrrman]

Something to try. No promises.

Pull the plug out of the wall (to make sure it's "all the way off").

Put the plug back in.

Put a finger on the option key and keep holding it down - don't let go.

Press the power-on button, DON'T let go of the option key.

Does the startup manager appear?

REASON WHY I asked you to do this:
Even though there's no other boot drive connected, it MIGHT be possible to create an external boot drive and get the iMac running that way. Again, no promises.

 

[Schnauzer World]

Something to try. No promises.

Pull the plug out of the wall (to make sure it's "all the way off").

Put the plug back in.

Put a finger on the option key and keep holding it down - don't let go.

Press the power-on button, DON'T let go of the option key.

Does the startup manager appear?

REASON WHY I asked you to do this:
Even though there's no other boot drive connected, it MIGHT be possible to create an external boot drive and get the iMac running that way. Again, no promises.

Thanks, I'll give this a try in a few minutes and let you know what happened.

 

[Schnauzer World]

Thanks, I'll give this a try in a few minutes and let you know what happened.

I unplugged it last night, so it had plenty of time to discharge I guess. But I get the same thing. Startup chime, screen slightly brighter than black, then about every 20 seconds it repeats endlessly until I unplug it.

Just a guess, but the night before it happened the power went out for a few seconds at my house during a mild rainstorm, no lightning. I was using the mac, but wasn't updating or anything. Maybe the firmware was damaged, then when I tried to update that's when the problem was exposed.

 

[Fishrrman]

Do you have access to another (m-series) Mac?

I'm thinking that it -might- be possible to use Apple Configurator 2 to either "revive" or "restore" the iMac. But you have to have a second Mac upon which to run it.

 

[Schnauzer World]

Do you have access to another (m-series) Mac?

I'm thinking that it -might- be possible to use Apple Configurator 2 to either "revive" or "restore" the iMac. But you have to have a second Mac upon which to run it.

I'll have one on Monday and I ordered a USB-C cable also from Amazon which is also needed. From watching a video on youtube, the newer macs can do it via finder without the Configurator.

I've done a lot of research and the revive/restore fixes the problem most of the time, one user had to replace a $750.00 circuit board at the Apple Store on the same mac as mine.

Apple needs to update their tech, you could fix what seems to be the equivalent of a BIOS on PC's so much easier without needing a second machine, the newer boards have two copies, just in case.

 

[Grumpus]

From watching a video on youtube, the newer macs can do it via finder without the Configurator.

Hi, could you please post the video link?

 

[Schnauzer World]

Hi, could you please post the video link?

Here you go, good videos, no annoying music and they get straight to the point.

 

[Grumpus]

Here you go, good videos, no annoying music and they get straight to the point.

Thanks, I was unaware that you could use Finder.

 

[Fishrrman]

Grumpus wrote:
"I was unaware that you could use Finder."

Can someone "point the way" to basic instructions as to HOW to use "just the finder" to do this job? I'm probably missing "what's right there in front of me", as usual. Thanks in advance.

 

[Grumpus]

Watch the second video posted above. (I hope it works better than using Finder to restore an iPod )

 

[Grumpus]

Also, see How to revive or restore Mac firmware.

 

[Schnauzer World]

Also, see How to revive or restore Mac firmware.

I just repaired the firmware and everything is working perfect again. I didn't have any luck using the Configurator App, but if the working mac has Monterey or newer you can just use Finder and that method worked smoothly.

Note:
When connecting in DFU mode, the borked mac will show up in finder on the left pane and there will be two buttons on the right revive and restore. On the iMac you plug the USB C cable in the port closest to the ethernet port. To put it in DFU mode, hold down on the power button while plugging it back in and hold for three seconds.

If you disabled T2 security to boot from USB, the process will enable it again, so you will need to disable it again if you install a fresh copy of macOS. I installed Ventura 13.7 and will probably not upgrade any further until support ends.

 

[Grumpus]

I just repaired the firmware and everything is working perfect again. I didn't have any luck using the Configurator App, but if the working mac has Monterey or newer you can just use Finder and that method worked smoothly.

Congratulations! Apple's documentation says the "working" Mac must be running Sonoma or higher to use the Finder method. What OS was your working Mac running?

If you disabled T2 security to boot from USB, the process will enable it again, so you will need to disable it again if you install a fresh copy of macOS.

Good to know about the T2, thanks.

 

[Schnauzer World]

Congratulations! Apple's documentation says the "working" Mac must be running Sonoma or higher to use the Finder method. What OS was your working Mac running?


Good to know about the T2, thanks.

Sorry about the late reply, I think it was Sonoma. I don't remember where I got the info it must be Monterey or higher.