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Modello A1312 / metà 2011 / Processore Core i5 da 2,7 e 3,1 GHz o Core i7 da 3,4 GHz, ID iMac12,2

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iMac stuck in boot loop. Can't get past WSOD.

I have a mid 2011 iMac 12.2 that suddenly restarted one day and is now stuck in a boot loop and never reaches the login screen. I keep getting stuck at a white screen.

Model Specifications

iMac 12,2 Core 2.7GHz i5 27-inch Mid-2011

Model A1312

Running on Sierra since it's release and never had any issues.

What I’ve Tried

• Resetting PRAM. (I hear the two chimes, attempts to load but gets stuck at the white screen. Eventually shuts off completely.)

• Internet Recovery Mode (Shows the globe, attempts to download files but then gets stuck at the white screen after loading.)

• Extended Apple Hardware Test. It took about 2 hours and 30 minutes. RAM showed as healthy and nothing else wrong noted in the tests.

• I ran Single User Mode and ran fsck -fy. Everything returned back OK. Nothing was modified or fixed.

• I tried booting into safe mode, but once it gets past the Apple logo it still shows a white screen with no login and then shuts down.

• I ended up creating an Ubuntu CD and started a live session. I managed to get in and read the drive and backup a lot of my files with no problem. I did however have to edit the Ubuntu boot config and run it in nomodeset. Otherwise I kept getting a black screen when Ubuntu tried to boot initially. I believe this instructs the kernel not to load the video drivers. (Possibly a bad GPU?)

• In regards to the above, I have not experienced any weird graphical glitches, lines or artifacts.

• I installed Sierra on an external USB hard drive that successfully boots on my Mac Air no problems, but fails to boot on the iMac. It attempts to load but when finished it goes to a white screen still.

• A week before it died, I noticed a weird symptom. My Apple keyboard would suddenly get set to Caps Lock, especially when coming out of the screen saver. I would have to unplug the keyboard from the back of the iMacs USB port and plug it back on as toggling the key had no effect. (Points to a possible logic board issue?)

I am having a hard time deciding what exactly may have went but I am leaning towards the logic board. It seems like the GPU and internal HDD are likely fine.

Any advice and input would be greatly appreciated.

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2 Commenti:

What happens when you go into Target Disk Mode holding the T key when you restart the system?

Reference: Mac startup key combinations

da

Hey Dan. When I boot into Target Disk Mode it shows the Thunderbolt and Firewire icons moving across the screen.

da

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OK, Thats rules out a bad logic board & per supply. You now need to diagnose the HDD using a second Mac can you access the iMac’s HDD using Target Disk Mode?

If you can you’ve narrowed the issue down to your GPU board which will need to be replaced.

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I will try this today and let you know. Thanks!

da

Hi Dan I can confirm that I can read the HDD files correctly in Target Disk Mode. Is the GPU not used in any of these modes? I was just wondering why I don't experience any artifacts or graphical glitches if the GPU is bad. Especially since Ubuntu looked fine when booted from a CD. I assume the GPU drivers don't get loaded unless booted into the Apple OS and at the login screen?

da

Your system has two graphics engines the Intel CPU and then the dedicated AMD GPU. Target Disk Mode and Ubuntu both use the intergraded graphics engine.

da

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Anthony sarà eternamente grato.
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