Displays reset to mirrored on restart

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Displays reset to mirrored on restart

I bought a new new iMac (Retina 5K, 27-inch, 2017) a few weeks ago to replace my late-2011 iMac and I'm getting a problem that I never used to get whenever I restart the computer :

I keep a Sony TV connected which I use as a second display, with the 2 screens arranged beside each other in the "extended desktop" mode in the Display settings. When I restart the computer the Display arrangement resets itself to Mirrored display, and consequently the display resolution on the iMac screen switches to 1920x1080. So each time I restart a have to open the Display settings, uncheck the Mirror Displays option (and then the resolution reverts back to the iMac default), and then reset the arrangement of the screens.

I can't find any way to stop this from happening! I called Apple Support and they were sympathetic but unhelpful; they said this was by design and there was no way to prevent it from happening. They said it was something built in to either the new iMacs or the OS (or both). It never used to happen with my old iMac, which was running the most recent (at the time, in late March) version of High Sierra. It sounds like they didn't know why it was happening and were just saying something instead of admitting that. But maybe this really is a "feature" of the new iMacs? If so, there is no mention of it in the Support documents on using multiple displays.

At any rate, I'm running the latest version of High Sierra, 10.13.4 and the TV in question is a 42" Sony Bravia HD connected via a thunderbolt to HDMI cable. Any help, or even similar tales of woe, is appreciated.

iMac with Retina 5K display, macOS High Sierra (10.13.4)

Posted on May 22, 2018 11:03 AM

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Answer 1

den.thed

Level 10

91,306 points

May 22, 2018 11:36 AM in response to Shortfatsteve

What steps did Support suggest and/or have you try....?

First off I would reset the NVRAM, as per > How to reset NVRAM or PRAM on your Mac - Apple Support

Then I would try a different Mini DisplayPort to HDMI adapter and cable or adapter cable.

Lastly I would Sleep the Mac 24/7 instead of shutting it down, same as I've done with all our Mac models over the years.

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Answer 2

May 24, 2018 7:08 PM in response to den.thed

Thanks for the reply. Like I said in the OP, Apple Support literally offered no suggestions, let alone solutions : they asked me to hold while they consulted with someone else and came back saying this was a feature, not a bug. (I should probably call back and see if I can get someone more motivated to solve this.)

I just tried resetting the NVRAM and it didn't have any effect -- too bad. When I read that I thought it had to be the solution. I've also tried two different cables, one that's TB to HDMI male and another that's an adaptor TB to HDMI female with a regular HDMI cable plugged into it. No difference with either one.

Also, I do usually sleep my Mac. I never really shut it down; I just have to restart it from time to time, like with OS updates or when things start to get squirrelly.

That does remind me though, when I did the OS update from 13.3 to 13.4, after the restart that time I didn't have the mirrored display problem. So I assumed it was a known issue that they had patched with the update. But no such luck : the problem came back with the next restart. Maybe there's something to learn from that? I wonder if there's one or several Display settings files that are corrupted that I could delete or something?

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Displays reset to mirrored on restart

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