MBPr 2015 15" and external monitor question

Discussion in 'MacBook Pro' started by RedOctober, Aug 31, 2015.

  1. RedOctober macrumors regular

    RedOctober

    Joined:
    Mar 14, 2015
    Location:
    West side of Oz
    #1
    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.
     
  2. Tankmaze macrumors 68000

    Tankmaze

    Joined:
    Mar 7, 2012
    #2
    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.
     
  3. priitv8 macrumors 68020

    Joined:
    Jan 13, 2011
    Location:
    Estonia
    #3
    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.
     
  4. RedOctober, Aug 31, 2015
    Last edited: Aug 31, 2015

    RedOctober thread starter macrumors regular

    RedOctober

    Joined:
    Mar 14, 2015
    Location:
    West side of Oz
    #4
    Thanks Tankmaze, I'll give that a go in the couple of days and report back.

    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.
     
  5. priitv8 macrumors 68020

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    Jan 13, 2011
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    Estonia
    #5
  6. dsmedic10 macrumors member

    Joined:
    Feb 16, 2015
    #7
    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.
     
  7. RedOctober thread starter macrumors regular

    RedOctober

    Joined:
    Mar 14, 2015
    Location:
    West side of Oz
    #8

    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.
     
  8. RedOctober thread starter macrumors regular

    RedOctober

    Joined:
    Mar 14, 2015
    Location:
    West side of Oz
    #9
    OK, tried the PRAM and SMC reset. No joy. Might wait for zambz to get a response from Apple.
     

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