Intel iMac won't boot from external SSD anymore

[suburbia]

Hello ladies and gentleman,

iMac 3.7GHx 6-core Intel i5 27-inch 2019, running Monterey 12.6.9 from an external SSD. The internal fusion drive isn’t bootable since Carbon Copy Cloner didn’t (couldn’t?) include to copy the OS when copying— so no OS installed on the internal fusion HD. Intended to install Ventura, or Sonoma in a few weeks when it’s released. Huge regret now for waiting...

• The Magic Mouse 2 was behaving oddly and since its p-lists docs were missing from Preferences, decided to restart.
• Upon restart, decided to reset the PRAM.
• This is when the iMac decided to misbehave. Wouldn’t continue to load and silently shut down.
• Wouldn’t start up when the power button is pressed.
• Unplugged and powered up to restart with Option key. The option to choose the external SDD is available. But once it’s selected and starts to boot, it silently shuts down again.
• Attempted start up from macOS Recovery System. Silently shuts down.
• Attempted start up from macOS Internet Recovery. Took 30 min to load and proceeds to restart. But silently shuts down again.
• Using another iMac now. Plugged in the external SSD that I regularly boot from on the 3.7Ghz iMac. It seems to be working and not dead. It’s just not available as a startup disk under System Preferences since the iMac I'm writing this from is not supported.

Any help would be so much appreciated, as this is my main workhorse.

TYIA!

 

[ifrit05]

While booting, hold down Command and V, it will give more details on what's happening behind the scenes.

 

[Fishrrman]

The "replacement" iMac...
Which one, what year?
What kind of DRIVE is inside?

Will the replacement boot to internet recovery?

 

[DeltaMac]

The "silent" shut down at boot can be a failing hard drive (the hard drive portion of your Fusion drive)
If that internal drive is failing, or has failed, it can (under some conditions) prevent booting from any device -- because the internal drive doesn't pass the self test, and then calmly shuts off the Mac.
Have you ever tried booting to Diagnostics, just to see what might be reported?

Use Apple Diagnostics to test your Mac - Apple Support

Apple Diagnostics, formerly known as Apple Hardware Test, can check your Mac for hardware issues.

support.apple.com

 

[suburbia]

Thank you everyone for the help. Very much appreciated.

Diagnostics comes back with “No issues found”. Which actually makes the issue more frustrating, since there clearly is an "issue".

Still attempting Internet Recovery: It seems to download since it’s the usual 25min time to download the OS, then it gets to the Apple icon loading progress bar, the screen will black out, the Apple icon and progress bar will appear, this time with the chime… then a message “Your computer restarted because of a problem…"

 

[Chuckeee]

Could be a power supply issue. Are the shutdown orderly or do you get a warning (your computer was not properly shut down) when you start up again.

 

[DeltaMac]

You can now say that the diagnostics did not find an issue. That test doesn't look at everything, but you can say that it is probably nothing that is a part of the electronics, such as memory, or the chipset, or a problem with the fans.
But, because the storage is part of the power-on self test (POST), the diagnostics doesn't really check that. So, that leads me to now think the storage is more likely the problem. And, of course, as the power supply is needed for everything, I don't think you can rule that out, either.
If this were my Mac, I would open up the case, then simply disconnect the SATA drive (the spinning hard drive), then try to boot from your external again. If you can boot (when you could not before), then I think that will tell you that the hard drive will likely get your iMac working again. If you disconnect the HDD, and the iMac still powers off, then that makes the power supply a likely culprit.

 

[suburbia]

Thank you for the suggestion. No warning at all.

The Internet Recovery Mode process stalled about a 1/3 of the way through last night, and I allowed it to stay that way from Sunday at approx 9pm until this morning 7am.Then just power off when I realize it wasn’t progressing any further. Would an issue with the power supply not shut down the iMac sooner…???

It's not shut downs in the true sense; the screen will go to black, but the iMac is still on. Something is preventing the various processes to reach completion, whether that’s Internet Recovery Mode, or attempt at booting from the external SSD. The message “Your computer restarted because of a problem…” but apparently Diagnostics claims “No issues found” (in only 2 minutes of evaluation…???).

 

[suburbia]

You can now say that the diagnostics did not find an issue. That test doesn't look at everything, but you can say that it is probably nothing that is a part of the electronics, such as memory, or the chipset, or a problem with the fans.
But, because the storage is part of the power-on self test (POST), the diagnostics doesn't really check that. So, that leads me to now think the storage is more likely the problem. And, of course, as the power supply is needed for everything, I don't think you can rule that out, either.
If this were my Mac, I would open up the case, then simply disconnect the SATA drive (the spinning hard drive), then try to boot from your external again. If you can boot (when you could not before), then I think that will tell you that the hard drive will likely get your iMac working again. If you disconnect the HDD, and the iMac still powers off, then that makes the power supply a likely culprit.

This scares me. Never cracked one of these iMacs opened before. And that fused SSD....

 

[HobeSoundDarryl]

No need for fear. Look around your area for a computer shop that works on Mac but is not Apple. Call them and tell you have the iMac you have and ask them what they will charge to replace the fusion with an SSD drive you have. If the price is not too bad, buy whatever amount of storage you probably want until you are done using that iMac (vs. buying it from them and it probably having a markup) and take both iMac and drive to that shop for the service.

After it is done, you'll have a faster iMac (all SSD will roar vs. fusion) and likely be good for at least a few more years until Apple decides to vintage it. And even after Apple quits on it, Windows 10 will likely run well on it until 2029 or so if you have any occasions where you need a PC.

 

[ifrit05]

I still say try to boot with verbose mode (Command+V) to see what's happening first.

 

[suburbia]

Thank you again for the suggestions. Just sent for a quote to the local Mac reseller.

I did boot up in verbose mode. Whatever script was revealed went by so fast, that I wasn't able to scroll though to make sense of any of it, nor input “reboot", only to have the screen turn to black within 30sec.

 

[suburbia]

Depending on my nerves, will be giving iFixIt or OWC kits a go. Either that, or taking it to the local reseller to have them install it.

When I wiped clean the internal fusion drive, there were 2 HD icons showing on my desktop for them. DIdn’t think anything of it then, but realized that it’s because it’s the split SSD and HDD…??? Once CCC backed everything but the OS (I assume onto the HDD?)— the other (SSD) was blank. In my ignorance, I deleted the blank disk in Disk Utility. Did I deleted the SSD? Did this cause the current chaos? Is there anyway to remedy? What happens when a new SSD takes the place of the old HHD? Will the soldered SSD be ignored -- or will it cause conflict?

 

[Chuckeee]

Usually when you delete an entire disk, it is actually just unmounted (or ejected for removable). Reboot and Run disk utilities again and check if that is the case

 

[suburbia]

Understood. Thank you.

If only I could access Disk Utility... Internet Recovery Mode just can’t seem to make it to the Disk Utility access screen— that’s the problem. If it were able to make it there, I could at least access Disk Utility, external SSD to boot from, Time Machine etc. The internal HDD isn’t offered as an option when booting with Option key: Just the external SSD and Time Machine. and in both cases, startup screen will load a1/3 of the way in the progress bar, then… black screen.

 

[DeltaMac]

You did say that you "wiped clean the internal fusion drive", which certainly split the fusion drive, so both devices show up on the desktop. That's what you said.
And, if you did successfully wipe the internal drive, then it will not have any boot system on the drive, and therefore will not appear as a boot option (there's no boot system installed, because you erased it.)
All you need to do now is reinstall macOS on the internal drive. That will be worth the wait until AFTER you (or someone else that you choose) replace the internal hard drive, with an SSD. I still suspect that replacing the hard drive will also fix your booting problems.

 

[suburbia]

Just a quick update: It was the HDD-- along with bad RAM. Replaced with an SSD and new RAM and the machine is good to go.

Thank you everyone for their help!