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User profile for user: rw5373
rw5373 Author
User level: Level 1
16 points

MacBook Pro 16inch not recognising external display when restarting in Clamshell Mode

I have a MacBookPro 16inch with the AMD Radeon Pro 5500M 4 GB option.


When I connect it to my external monitor (DELL UP2715K) and close the life - it works fine in Clamshell mode.


However - if I have to restart the Mac for any reason - the Mac doesn't recognise the external display and it stays black. However, when I then open the MacBook up - the internal display also doesn't come on. You can hear the Mac whirring and running - but neither display ever shows anything.


Then - if I hit the power button to shut the Mac off and start it up again, this time with the lid open - I get loaded into the password recovery utility.... which I then have to qui, restart the Mac with lid open, wait for it to load up - then close the lid to get back to clamshell mode.


Any thoughts in the hive mind?


Robert

MacBook

Posted on Dec 24, 2019 3:11 AM

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User profile for user: CarlAVII
CarlAVII
User level: Community Specialist

Posted on Dec 26, 2019 1:30 PM

Hi there, Robert.


I see that you're having a problem using an external monitor with your 16-inch MacBook Pro. It's fine up until you need to restart your computer. Neither display will work, and I'm glad to help.


Reset NVRAM or PRAM on your Mac -- Reset the nonvolatile random-access memory (NVRAM) using the steps in this article. Once you're back to the Desktop, see if you're able to use the either display after restarting.


About macOS Recovery -- Restart your Mac in Recovery mode, and place your Mac in closed-display mode, then restart back into Recovery mode again. See if both displays work as expected.


How to test an issue in another user account on your Mac -- If the issue persists, use this article to create and test a new administrative user account. This will demonstrate if the issue is isolated to your account, or if it's system wide.


Let me know how that goes, and take care!

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User profile for user: CarlAVII
CarlAVII
User level: Community Specialist

Dec 26, 2019 1:30 PM in response to rw5373

Hi there, Robert.


I see that you're having a problem using an external monitor with your 16-inch MacBook Pro. It's fine up until you need to restart your computer. Neither display will work, and I'm glad to help.


Reset NVRAM or PRAM on your Mac -- Reset the nonvolatile random-access memory (NVRAM) using the steps in this article. Once you're back to the Desktop, see if you're able to use the either display after restarting.


About macOS Recovery -- Restart your Mac in Recovery mode, and place your Mac in closed-display mode, then restart back into Recovery mode again. See if both displays work as expected.


How to test an issue in another user account on your Mac -- If the issue persists, use this article to create and test a new administrative user account. This will demonstrate if the issue is isolated to your account, or if it's system wide.


Let me know how that goes, and take care!

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User profile for user: rw5373
rw5373 Author
User level: Level 1
16 points

Dec 27, 2019 4:34 AM in response to CarlAVII

Hi Allen A


Thanks for the suggestions.


NVRAM reset - I had already tried, but repeated - but it didn't change things.


Recovery mode..... I found an odd thing - I don't think recovery modes supports external monitors (it did on my 2015 MacBook!)..... when I launch recovery mode whilst in clamshell mode, the external monitor shows the apple logo whilst the OS loads.... but then goes black and the signal is lost - and I have to open the MacBook up - at which point you find the recovery mode opening menu on the MacBook screen and you can proceed from there.


Which is an interesting side note....


But having launched into recovery mode a couple of times and then back into normal OS.... that seems to have cleared the problem and now restarting in clamshell mode works fine.


How very odd - but at the same time - happy days it is now working!


Thanks for the input


Robert

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MacBook Pro 16inch not recognising external display when restarting in Clamshell Mode

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