After iMac wakes from sleep, three monitors turn on, go black for a couple of seconds, then back on again.

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After iMac wakes from sleep, three monitors turn on, go black for a couple of seconds, then back on again.

I have two external monitors connected to Thunderbolt 2, one a VGA monitor and the other an HDMI monitor. After waking from sleep all three monitors come on, then all three go black for a couple of seconds and then back on and then work fine until next time it goes to sleep. Same thing each time it wakes up.

An Apple support tech told me recently that this is a known problem, but I don't see any help here in the Communities.

I can live with this, but it is annoying. I'm running BigSur 11.5.2 in a mid 2015 iMac Retina 27".

Anyone else see this problem? Any fixes?

Thanks,

iMac 27″, macOS 11.5

Posted on Sep 4, 2021 12:12 PM

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Answer 1

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hcsitas

Level 6

12,914 points

Oct 4, 2021 10:35 AM in response to veehbJ

Yes, Yes and Yes. The iMac does sleep and for mechanical drives like yours, does save power. Nonetheless, because of the diversity of monitors out there, wake issues like the one you’re seeing, are common. As such, the best solution today is to do away with Sleep.

While it’s logical to point to the Mac as being the cause, fact is, almost all monitors come with no certified testing on Macs or Mac-specific drivers. Which puts the ball squarely in their court. Waiting for a fix from Apple IMO is pointless until that changes (which doesn’t seem likely).

That said, it’s not a reason to write off your Mac unless future upgrades come with features you can’t do without. I have a 2013 iMac that’s full-stopped on Catalina nonetheless shows no sign of running less than perfectly all the time. Your mileage may vary but my guess is that your iMac is good for at least until 2025.

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Answer 2

veehbJ Author

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55 points

Sep 4, 2021 1:10 PM in response to hcsitas

Thanks for the suggestion. This will probably work as it won't go to sleep.

I really don't want to disable sleeping. I use my computer several times a day and I want it to sleep when I'm not using it. I don't want to shut it down for long absences of time. There must be something else i can do.

Is there no known cure for this problem? I've spent a lot of time browsing the user comments and haven't seen any one else with this same problem. Let's wait and see if there are any other suggestions.

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Answer 3

veehbJ Author

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Oct 4, 2021 9:49 AM in response to veehbJ

Interesting that after a month, no one else has replied to this with a solution or a better suggestion.

One of the Apple Senior Support Techs. told me a couple of months ago that this is a known problem. He didn't have easy access to a fix.

Is there no fix for this? Just annoying to have to wait a few seconds before I can use the computer when it has been in sleep mode.

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Answer 4

hcsitas

Level 6

12,914 points

Oct 4, 2021 9:55 AM in response to veehbJ

Sleep serves no purpose on later Macs, all pain, no gain. Sleep the monitors using the automatic timer in Energy Preferences and shut for long absences. That’s it. You don’t need another solution (but sure, you can wait).

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Answer 5

veehbJ Author

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55 points

Oct 4, 2021 10:18 AM in response to hcsitas

OK, I'll try it. Thanks for asking again.

Do I uncheck "Put hard disks to sleep when possible"? and Also uncheck "Wake for network access"? and uncheck "Enable Power Nap"? All three of these are currently checked.

So does the iMac no longer sleep?

Mine is an older one, from 2015. It is the 27" with 5K Retina display and 1TB 7200 rpm hard drive. I have heard that the next MacOS upgrade will not support this iMac. I really have enjoyed and used this iMac. Very few problems over the years. It will be a shame to have to retire it!

I appreciate your suggestions!

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Answer 6

veehbJ Author

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55 points

Oct 4, 2021 6:52 PM in response to hcsitas

hcsitas,

Thank you for your great suggestion. I checked the box, "Prevent computer from sleeping automatically when the display is off". Your answer to my question about unchecking the three other boxes is confusing. Should these three boxes be checked or unchecked? Makes sense to put the hard drive to sleep to extend it's lifetime. So I checked that one. Not sure about the other two. I assume I should uncheck them. Not sure what a "Power Nap' is. Which of these boxes do you suggest I check?

Here is a screen shot of the current settings on the five boxes:

I took your suggestion and disabled sleep and when I went back to my computer several hours later, the screens were blank. I hit a keyboard key and all three came back on and they did not go black again a few seconds later. Also Time Machine did backups while I was gone. So your suggestion works.

Thanks again!

Also, Thanks for the suggestion to keep this iMac, even if it is not covered with the next MacOS upgrade. It's probably the best computer I've ever owned and that goes back a long, long time. Part of the reason it runs so well, is that I've had excellent support from Apple, even after Apple Care ran out.

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