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MBPr 2015 15" and external monitor question

RedOctober

RedOctober

macrumors regular
Original poster
Mar 14, 2015
194
532
West side of Oz
Hi all,

I just bought the missus a 15" MBPr with the 370x GPU and I connected a Dell 2312 monitor to it via a minidisplayport to DVI adaptor. The problem is that when this adaptor is connected to the macbook, it only displays on the external monitor, the LCD stays dark. If I unplug the adaptor, the LCD will be on. Once I plug the adaptor back in, I'm back to 2 screens.

Now I'm assuming that this is a 'feature' where the macbook thinks we are working with the external monitor only, ie clamshell mode even thought the LCD is open but other than forcing the macbook to detect displays, is there any other way to make the macbook boot with both screens active?

Oddly enough, my old mid 2012 13" macbook pro doesn't have this issue.
 
Thats strange, mine doesn't work like that. if I connect the mbp to external monitor both screen would turn on. If I closed the mbp the external monitor would on and the internal obviously turn off. but when I open it again both monitor would turn on.

Try to reset SMC and do PRAM reset.
 
Why have DVI in the equation? Doesn't the Dell have DisplayPort connector? So you could use a simple DP cable with a mini connector on one end.
 
Tankmaze said:
Try to reset SMC and do PRAM reset.
Click to expand...

Thanks Tankmaze, I'll give that a go in the couple of days and report back.

priitv8 said:
Why have DVI in the equation? Doesn't the Dell have DisplayPort connector? So you could use a simple DP cable with a mini connector on one end.
Click to expand...

That's a good point, it's just that we had some spare MiniDisplayPort to DVI adaptors lying around. I'll try a miniDP --> HDMI cable if the SMC and PRAM reset don't work.
 
Last edited:
RedOctober said:
I'll try a miniDP --> HDMI cable if the SMC and PRAM reset don't work.
Click to expand...
Why not DP-mDP?
MDP2DPMMX.main.jpg

6 ft Mini DisplayPort™ to DisplayPort 1.2 Adapter Cable M/M - DisplayPort 4k
 
Is your Mac connected to power BEFORE you turn it on? I ask because I think the monitor/laptop display behavior is different depending on whether you have power attached or not. I'm just guessing here though.

I attach my Macbook to a thunderbolt dock w/ my external LCD attached to the dock via thunderbolt-to-DVI. I plug in power then the dock (while the macbook is closed) and shake my external mouse and the display lights up.

If I do this while the laptop is open, the laptop display "flashes" while I plug in the Dock, but otherwise stays on.

Maybe your mac is having a glitch with the dGPU switching? When using your Mac, typically you are using the iGPU. However when you plug in an external display, your Mac automatically switches to the dGPU, no matter what application you are currently using. Maybe when this happens your internal display (Mac display via iGPU) is 'disabled'. When you plug in the display the second time (unplug/re-plug-in), the hardware recognizes the external display correctly and you end up with two displays.

In my case the external and internal displays work as expected, but maybe because you have a dGPU it's flakey.
 
dsmedic10 said:
Is your Mac connected to power BEFORE you turn it on? I ask because I think the monitor/laptop display behavior is different depending on whether you have power attached or not. I'm just guessing here though.

I attach my Macbook to a thunderbolt dock w/ my external LCD attached to the dock via thunderbolt-to-DVI. I plug in power then the dock (while the macbook is closed) and shake my external mouse and the display lights up.

If I do this while the laptop is open, the laptop display "flashes" while I plug in the Dock, but otherwise stays on.

Maybe your mac is having a glitch with the dGPU switching? When using your Mac, typically you are using the iGPU. However when you plug in an external display, your Mac automatically switches to the dGPU, no matter what application you are currently using. Maybe when this happens your internal display (Mac display via iGPU) is 'disabled'. When you plug in the display the second time (unplug/re-plug-in), the hardware recognizes the external display correctly and you end up with two displays.

In my case the external and internal displays work as expected, but maybe because you have a dGPU it's flakey.
Click to expand...


Hi, yes, the external monitor is connected to the MBPr first then I power on the laptop. In this case, only the external monitor shows the display, the laptop LCD is black. It's as though the mac thinks it's in clamshell mode, even though the LCD is open.

If I remove the miniDP adaptor from the laptop, power it up (which causes the LCD to show the display), then plug the miniDP in, the laptop will detect the external monitor and fire up the display.

The workaround I found was to call up system preference --> display --> [Option key] and do a Detect Displays. It will then fire up the LCD display and everything is sweet. It's just annoying having to do this all the time.

It is possible that the mac has an issue. I'll reset the PRAM and SMC tonight and see how that goes. If not, I'll bring it to the store.
 
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