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iMac (mid 2011, running OS X 10.12) gets stuck on white screen (after playing the chime sound and displaying the Apple logo and progress bar) when I try to

  • boot normally
  • boot in safe mode (holding down Shift while booting)
  • boot in recovery mode (pressing Cmd+R while booting)

Sometimes the progress bar will run all the way (followed by a white screen), sometimes the white screen interrupts before the progress bar is finished. The progress bar for recovery and safe mode looks the same as the normal progress bar—not sure if that's normal for Sierra but it seems strange, as if it's not really booting into safe mode or recovery mode.

Resetting NVRAM (Cmd+Option+P+R) and SMC (disconnecting power for 30 seconds) didn't help.

Booting while pressing Option gets me to the partition selection. There, I can choose between my normal boot drive (256 GB SSD with the OS), my Windows 8 partition and the recovery partition. Booting to Windows results in a black screen right before the login screen would normally appear. Booting to the recovery partition results in a white screen.

Booting in verbose mode (Cmd+V while booting) rushed through a wall of text seemingly normal before getting stuck on white screen again when—I would assume—the login screen would have shown normally.

I was able to enter Apple Hardware Test once by pressing D during boot, but it appeared to be stuck after a while, so I didn't let it finish. If I'm holding down D now while booting, the machine enters Internet Recovery Mode, same when I hold down Cmd+Option+R. Entering Internet Recovery Mode produced the -6003F and -6003D errors once each. After that it got to the progress bar and the estimated time remaining, but appeared to get stuck (time remaining was 24 hours and not moving, same for the progress bar). When I tried again, it got stock on the "Starting Internet Recovery / This may take a while" screen (unless it might take an hour in which case I might have ended it prematurely).

I was able to start the machine up in Target Disk Mode (T during boot) after connecting my MacBook via Thunderbolt 2. I was to able to completely mirror both, the iMac's SSD (OS disk) and the HDD. No files seem to be corrupted.

Curious detail 1: When trying to boot either normally, into safe mode or into recovery mode and the white screen interrupts the progress bar, in that moment the screen brightness is slightly dimmed.

Curious detail 2: The chime sound was notably quieter for all the boot attempts until I reset the NVRAM. The first of the two chime sounds that play during that procedure was still quiet, the second one was at normal volume again.

Curious detail 3: All built-in LEDs of my Matias Tactile Pro keyboard (1. caps lock, 2. the key that would be num lock on a Windows keyboard and 3. F14) light up for a few seconds immediately after turning on the iMac. After a few seconds they turn off again. When the iMac was operating normally this never happened.

Question: Is it safe to assume that something inside is fried and there'll be no way around a visit and repair at the Apple store?

Edit: I guess one remaining option is trying to boot from a flash drive. Will try that if it turns out that Internet Recovery really is stuck when I check its status again tomorrow.

Edit 2: As per klanomath's suggestion in the comments, I tried booting the iMac from the MacBook's OS disk via TDM and vice versa. When the MacBook is in TDM and I select its OS disk as the disk to boot the iMac from, it does the progress bar into white screen charade on the iMac. When the iMac is in TDM and I try to boot the MacBook from the iMac's OS disk, the MacBook's screen stays dark after the chime sound. It doesn't even get to the disk selection screen while holding Alt. Also, it takes considerably longer (12 to 20 seconds roughly) for the chime sound to play on the MacBook after turning it on when the iMac is connected via Thunderbolt while the iMac is in TDM. Without the two being connected (or when the iMac is turned off), the chime sound plays after maybe 3 to 5 seconds after turning on the MacBook.

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    btw, AHT always looks like it's stuck. Be patient. If the cursor will still move [even very jerkily] it's still thinking. Mem tests are at least 1hr per GB. Also note, that machine is old enough that the PRAM battery may be failing [something I spent 3 pointless days recently ignoring :/ & results on AHT if so may be considerably skewed. – Tetsujin Dec 13 '17 at 21:08
  • @Tetsujin That's very valuable information, thanks! Unfortunately, I'm not able to access AHD anymore. Instead, when pressing D, "Starting Internet Recovery" appears. Right now I'm at the spinning globe, non-moving progress bar and 24:00 hours remaining state again. Just let it run until at least tomorrow? – S. R. Dec 13 '17 at 21:12
  • It may be worth a bit of patience, but if no joy, it's possible to boot most Macs from a USB holding the specific AHT for that model. A method to make the USB key & a comprehensive list of downloadable model-specific AHT versions is held at github.com/upekkha/AppleHardwareTest – Tetsujin Dec 13 '17 at 21:16
  • @Tetsujin Thanks again for the advice, these will definitely be the next steps I'll try before taking the machine to the store. – S. R. Dec 13 '17 at 21:23
  • A possible short-cut to eliminate a hardware error is: 1. start the iMac in Target Mode, attach it to the MacBook and try to boot the MacBook to the iMacs main macOS volume. 2. Shutdown everything 3. Start the MacBook in Target Mode, attach it to the iMac and try to boot the iMac to the MacBook's main macOS volume. – klanomath Dec 13 '17 at 22:08
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It's very likely to be the video card. There was a repair extension program (since expired) for the AMD GPUs in 27" 2011 iMacs. They will boot to the Apple logo/progress bar and then hang at a white screen or pink/green lines.

If you're near an Apple Store at all you should take it in or at the very least call Apple and do some troubleshooting. Stores in most of the US (except California, where the timeframe is quite a bit longer) will not carry parts for the 2011 iMacs much longer, likely stopping as soon as a few weeks from now since its been about 5 years since they were discontinued in all markets.

  • Thanks for that! I'll get in contact with my local Apple store (am from Berlin) and ask if the issue sounds familiar. If they know right away that the GPU would need to be changed, I might just retire the whole machine. – S. R. Dec 13 '17 at 22:56
  • I don't know what the laws are like regarding known manufacturing defects in the EU, but maybe they'll be able to fix it for you in a cost-effective (or free) manner if that's what it turns out to be. I wish you luck! – Jess Dec 13 '17 at 23:03

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