iMac 27-inch Retina 5K display randomly shuts down and then requires SMC reset to boot

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iMac 27-inch Retina 5K display randomly shuts down and then requires SMC reset to boot

iMac 27-inch Retina 5K display randomly shuts down, and then requires SMC reset to boot. It may happen while working with it, or while idle. In normal booting or even in Safe Mode booting. May happen a few minutes after booting or after several hours.

Resetting PRAM or SMC does no fix it. The issue arose with macOS 11.3.1 (20E241) Big Sur, after upgrading from macOS 10.12.6 (16G2136) Sierra. The Mac is shutdown all days overnight.

System: macOS 11.4 (20F71) Big Sur on iMac18,3 (mid 2007). Booting from Samsung Portable SSD T5 2TB.

Posted on May 29, 2021 11:57 PM

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Answer 1

CarlAVII

Community Specialist

May 30, 2021 6:24 PM in response to ApMaX

Hello ApMaX and welcome to Apple Support Communities. It appears you are having some difficulty with the display on a 2017 iMac.

When this happens, does the Mac itself shut down or just the display? If you can still hear system sounds when the display is dark, that would isolate this to a display issue. Another approach is to take a screenshot with the display dark (Command + Shift + 3). Upon restart, take a look at the screenshot. If there is not screenshot saved to the desktop, then the Mac itself is shutting down. If there is a file but it is just a black rectangle, then the issue would be isolated to the GPU as a screenshot is actually the output of the GPU and not a picture of the screen. If there is a file and it contains an image, then the issue is with the display.

The one thing unusual about your situation is that you are booting from an external drive? Is this because of a problem with the internal drive or are you just trying to get better performance than with the spinning drive? If it's the latter, does this occur if you boot from the internal drive rather than the external?

Cheers.

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Answer 2

chuck_3rd

Community Specialist

May 31, 2021 12:45 PM in response to ApMaX

Hi ApMaX.

Yes, as the options for screenshots in macOS have expanded to include things like taking a screenshot of a specified area, additional key combos have been added for these capabilities that once required standalone third-party apps. Command + Shift + 5 will open a screenshot and display toolbar/menu. Command + Shift + 3 has been part of the Mac universe for a very long time and will still serve to quickly take a shot of the entire screen.

You have done a good job of isolation thus far. As the drive is being used with a different mac of the same model and vintage without issue, it would prompt starting to consider hardware issues. As the SMC deals with power-related issues and the Mac is shutting down and will not boot again without resetting the SMC, the probability of this being a power-related hardware issue grows.

At this point, you'll want to have the Mac physically inspected.

Contact Apple for support and service

Cheers.

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Answer 3

ApMaX Author

Level 2

159 points

Jun 1, 2021 6:06 AM in response to chuck_3rd

Thanks.

Command Shift 5

works here in the same way as when opening "/System/Applications/Utilities/Screenshot.app". On the other hand,

Command Shift 3

worked before, but does not work any more here with macOS 11.4 (20F71). Is that wrong? Is there other way to take a screen capture just with a keyboard combination, without having to select anything additionally? I mean, in relation to your suggestion to take a screenshot when the Mac showed a dark display.

I remember a similar issue with an older iMac G5/2GHz 20-inch back in 2006, due to a defective Power supply (replacing it fixed it), although in such a case I think that it was not required to reset the SMC.

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Answer 4

ApMaX Author

Level 2

159 points

May 31, 2021 1:39 AM in response to CarlAVII

Thanks. As said abobe, "iMac 27-inch Retina 5K display randomly shuts down and then requires SMC reset to boot".

So, the Mac shuts down completely (no just the display). Not only that. Then, does not turn on again pressing the power button. You must reset SMC for it to boot (disconnecting from mains, waiting 15 seconds, connecting to mains, waiting 15 seconds and pressing the power button).

Shift Command 5

is what works to take screen captures in macOS 11.4 (20F71) Big Sur, as shown here:

Take screenshots or screen recordings on Mac

https://support.apple.com/guide/mac-help/take-a-screenshot-or-screen-recording-mh26782/mac

That and carriage return takes no screen capture in the crashed Mac.

Booting from the external drive to work booting from it Macs at both home and work, using the same external drive (all your work in your pocket). The iMacs are the same model as described above, with fast 2 TB SSD inside (used only as Time Machine backup; the internal disk does not contain a bootable system). Only one Mac crashes.

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iMac 27-inch Retina 5K display randomly shuts down and then requires SMC reset to boot

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