Clamshell mode problem: laptop screen still active

Hi folks

I have a somewhat unusual problem. When running my Mac Air in clamshell mode, it still thinks its own screen is active. The laptop's screen is turned off, but when I move my mouse around the external monitor, it can drift off into the (closed, dark) monitor of the laptop itself. When I open Displays in the System preferences, it clearly thinks both screens are active.

Has anyone else run into this? Any suggestions on handling it?

Thanks in advance.

Try rebooting the computer.

- Nick

pigoo3 said:

Try rebooting the computer.

- Nick

Click to expand...

Thanks Nick, I should have said upfront that I have already tried rebooting, to no avail.

The problem appeared quite recently, so I wonder if there's an obscure setting somewhere that's somehow breaking this -- but I can't figure out what it would be.

cjh302 said:

Thanks Nick, I should have said upfront that I have already tried rebooting, to no avail.

Click to expand...

When you rebooted…was the MacBook Air's display closed & the external monitor connected?

- Nick

pigoo3 said:

When you rebooted…was the MacBook Air's display closed & the external monitor connected?

- Nick

Click to expand...

Yep, on both counts.

Ok…two other ideas:

- Do a NVRAM/PRAM Reset:
https://support.apple.com/en-us/HT204063

- Do an SMC Reset:
https://support.apple.com/en-us/HT201295

- Nick

pigoo3 said:

Ok…two other ideas:

- Do a NVRAM/PRAM Reset:
https://support.apple.com/en-us/HT204063

- Do an SMC Reset:
https://support.apple.com/en-us/HT201295

- Nick

Click to expand...

Hm, I've tried both but no joy. Thank you for the suggestions, though. It's a weird one, this.

Stupid question...
You are in mirrored mode right?

cradom said:

Stupid question...
You are in mirrored mode right?

Click to expand...

Not a stupid question! I'm not in mirrored mode, and I'm aware that I could use that to fix this -- but I often unplug my Mac from my desk and plug it into an external projector, at which point I don't want mirroring. Until now, I've never used mirrored mode, and this problem didn't happen... so I was hoping to find another solution.

(You'd imagine the system would be clever enough to *not* detect the laptop's screen when it's in clamshell mode... it certainly used to manage this!)

But maybe ticking the 'mirror' option and just messing with system preferences every time I connect to and disconnect from a projector is the easiest way to fix this.

cjh302 said:

I'm not in mirrored mode, and I'm aware that I could use that to fix this --

Click to expand...

Give it a try. The goal at the moment is to find a solution to the current problem. Let's worry about what happens later…later.

cjh302 said:

(You'd imagine the system would be clever enough to *not* detect the laptop's screen when it's in clamshell mode... it certainly used to manage this!)

Click to expand...

It usually is/does!

- Nick

pigoo3 said:

Give it a try. The goal at the moment is to find a solution to the current problem. Let's worry about what happens later…later.

Click to expand...

Good point, well made.

pigoo3 said:

And usually.when someone connects to an external projector.you want to be in "mirror-mode".since you want the external project or to mirror what's on the computer display.

Click to expand...

Yeah, I prefer to work without mirroring, but it's not a wildly big deal to mess with system settings each time I connect to / disconnect from a projector. And this does solve the problem!

pigoo3 said:

It usually is/does!

- Nick

Click to expand...

Gotta love technology, eh

My thanks to both of you for your suggestions and help with this issue. As a forum n00b, I very much appreciate the rapid and helpful responses

cjh302 said:

Gotta love technology, eh

My thanks to both of you for your suggestions and help with this issue. As a forum n00b, I very much appreciate the rapid and helpful responses

Click to expand...

Please let its know if changing to mirror mode setting helps. I run my 17" MacBook Pro in both extended desktop mode and clamshell mode (alternate between the two) all the time (almost never just use the MBP's built-in display only). And as far as I know…have not run into this trouble.

- Nick

And I assume all the requirements and quirks have been double checked??
https://support.apple.com/en-ca/HT201834

Next, try a Safe Boot to possibly eliminate any non-Apple software that could be causing the problem.

pigoo3 said:

Please let its know if changing to mirror mode setting helps. I run my 17" MacBook Pro in both extended desktop mode and clamshell mode (alternate between the two) all the time (almost never just use the MBP's built-in display only). And as far as I know…have not run into this trouble.

- Nick

Click to expand...

Yep, as expected mirror mode solves the problem. I've been running various Macs in extended desktop mode and clamshell for over a decade, and it's the first time I've run into this issue, too!

Thanks again.

pm-r said:

And I assume all the requirements and quirks have been double checked??
https://support.apple.com/en-ca/HT201834

Next, try a Safe Boot to possibly eliminate any non-Apple software that could be causing the problem.

Click to expand...

Just to confirm -- yes, I had tried the above, but to no avail. Thanks for checking.