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OS X 10.11.3: iMac 5K Screen Black Screen —Will not Wake Up From Sleep

The OS X 10.11.3 release notes are terse, but one note states:

Fixes an issue that may prevent some Mac computers from waking from sleep when connected to certain 4K displays.

I can now use three displays reliably (so far at least). But it comes with a new and very bad bug on a single-display system—the iMac 5K.

iMac 5K black screen — display stays black

I’ve been running the late 2015 iMac 5K since Dec 24—zero issues. Perfection until OS X 10.11.3.

The night before last, my iMac 5K was updated to OS X 10.11.3. Since then, if the iMac 5K goes to sleep mode (blank/black screen), the screen never again wakes up. The OS doesn’t crash; it’s just that it is unusable since the screen stays black. The only fix is to cut power and reboot, e.g. by pulling the power plug.

Yikes: disable sleep entirely, burning power and aging the display backlight, or effectively crash upon sleep? Clearly Apple has messed with the display code (see above 3-display discussion), introducing a new bug on a machine with only one display.

There may be wrinkles affecting things here:

  • Choosing Sleep manually from the menu then waking-up the iMac 5K is fine, as is a short sleep period.
  • There might be a time factor involved (sleep longer than X). The problem seems to happen only after a good amount of time (e..g an hour or more).
  • The problem might involve a device on the Thunderbolt bus (using OWC Drive Dock and Thunderbolt Networking).

In a 24-hour period, the “crash” has happened half a dozen times.

Well, when developers at Apple change code, they might fix something, but there is a very high risk of new bugs (a fact established over some years now). Apple Core Rot is spreading. It should be an embarrassment to someone at Apple: this is the kind of thing that quality assurance test suites should catch before shipping.

Fixing: who knows? I’m going to follow Windows protocol, which is now Apple OS X protocol: reinstall the OS. UPDATE: reinstalling the OS makes no difference; it seems to be a new bug with Thunderbolt devices: if no Thunderbolt device is attached, the iMac 5K wakes up properly.

Jon M writes:

I'm having the same sleep bug on the same iMac.

I agree that time seems to be a factor. It only happens at longer intervals and I do think it could be tied into a device on the Thunderbolt bus.

I have two Lacie 5Bigs and one Areca 8-bay raid, all connected via Thunderbolt. I haven't fully tested but sleep/wake does seem to work properly if I pull everything off of Thunderbolt.

MPG: Good to see confirmation.

JP M writes:

I am a subscriber to two of your offerings and I am reaching out to you (out of desperation). I recently purchased an new iMac 27 " 5K, in part due to your recommendation. Soon after I started my new computer and left it idle for a few minutes I noticed it went in to sleep mode. I wasn't alarmed until it wouldn't wake! I called Apple support (useless) but they just had me unplug the computer, wait 20 seconds and power the computer back on. It booted as normal and I thought this would be the end of it, but the problem reoccurred. Bottom line I took my new computer back to the Apple Store, they ran a diagnostic program and found nothing wrong. At their recommendation I returned the computer and ordered another, just in case it was a hardware issue.

While waiting on my new computer to arrive I started researching the issue and I am not alone in this issue, and there seems to be no consensus as to what the problem is and how to resolve it. I used the migration tool to set up my computer but others have done a clean install and having the same problem.

Can you offer any possible insight possible insights or solutions to the problem?
My configuration is 4 GHz quad core i7, 32GB RAM, 2TB Fusion Drive, AMD Radeon R9 M395.

MPG: manifest incompetence at Apple. It’s an OS X bug but they don’t even have tech staff aware of it.

Robert B writes:

Got this bug just last week awhile after updating to El Capitan......

Model Name: iMac
Model Identifier: iMac12,2
Processor Name: Intel Core i5
Processor Speed: 2.7 GHz
Number of Processors: 1
Total Number of Cores: 4
L2 Cache (per Core): 256 KB
L3 Cache: 6 MB
Memory: 8 GB
Boot ROM Version: IM121.0047.B23
SMC Version (system): 1.72f2

Had it dropped off at an Apple Authorized service depot after trying
fruitlessly to solve the problem, was sure it was hardware related,
backlight, video card etc. The no wake symptom occurred once at service and
was fine after that until I got it back home.

The problem then returned repeated just after a few minutes of use and not
even completing a reboot to the login, rebooting into internet recovering
the screen was stable but that would only allow reinstalling LION. The
screen was also stable after several attempts trying to get to recovery mode
and reinstall of 10.11.6 which was successful, hoping that had solved the

Currently at at 10.11.6.... unfortunately the problem has returned but so
far much less frequently, lowering the brightness with the F1 key caused it
twice to go into the black screen requiring a reboot other than that it has
been relatively stable but the bug continues to exist none the less.

MPG: Sigh. 11 months later and Apple still has not fixed the problem. A friend of mine has a problem whereby Safari hangs and I don't know how to fix it (I reinsty

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