I have an issue discussed previously on Ask Different but have not found a solution in my use case.

I have macOS High Sierra installed on a MBP 6,2 (i.e. a vintage 15" i5, mid-2010, NVIDIA GeForce GT 330M with 256MB VRAM).

With a new external monitor (Viewsonic VP3268-4K) set at 2560x1440 and connected with mini-DisplayPort to my MBP, the external monitor loses it's video signal when I try to deactivate the internal LCD display by clamshell-ing it (I use a refrigerator magnet to make the MBP believe the lid is closed).

However, this works fine when another external display (1920x1200) is connected via mini-DP --> DVI cable.

-- What Works --

Deactivating the unused MBP internal display worked fine with my older external monitor (1920x1200) connected to the MBP via mini-DP --> DVI adapter cable. When clamshell-ed the internal LCD display goes dark and also disappears from the System Preferences --> Displays --> Arrangements tab page. My mouse cursor remains only within the external display. Everything works as expected.

The new (2560x1440) external display connected via mini-DP works with no issues as long as the MBP internal display is also active. I can turn down the internal display's backlighting to remove the visual distraction, but this still leaves it's video framebuffer active: it is listed in System Preferences... and the mouse pointer is not restricted to the external monitor video space and can go off into the internal display area.

-- Fixes Tried so Far --

Lots of reading online, here (lots of good info) and other sites led me to try editing boot NVRAM parameters to force the internal display to be inactive, terminal commands suggested in other postings were tried (see below), different DP adapters, changing the new external monitor's settings: force DP v1.1. but nothing tried had the desired effect: to clamshell the internal display while using the external monitor (2560x1440) via DP. Unfortunately I cannot use DVI with the new external monitor because single channel DVI only supports (1920x1200) and I do not have a dual channel DVI cable or Apple cable adapter.

The terminal commands I've tried (after disabling SIP) are:

sudo nvram boot-args="niog=1"

sudo nvram -d boot-args

sudo nvram boot-args="iog=0x0"

sudo nvram boot-args=niog=1

I've also tried resetting the external monitor settings by removing the Folder ~/Library/Preferences/ByHost/

Can anyone offer any other suggestions?

  • Firstly, welcome to Ask Different! :) Some questions for you: (1) Have you tested to see what happens with the new Viewsonic display when the MBP is actually in Clamshell mode (i.e. the lid is actually closed)? (2) When you say "terminal commands suggested in other postings were tried", can you specify which commands? (3) Have you actually tried resetting the NVRAM? (4) Which version of the NVIDIA GeForce GT 330M graphics card do you have (i.e. the 256MB or the 512MB VRAM)?
    – Monomeeth
    Commented Aug 9, 2019 at 9:44
  • Thank you for the welcome and suggestions. Commented Aug 9, 2019 at 21:22
  • Answering suggestion (1) - Physically closed the MBP lid which caused the new external monitor (2560x1440) to go dark "no signal". Hit keyboard SPACE key and moved the mouse intermittently over a period of 60 seconds attempting to wakeup the video link, but this was not successful. Then turned the external monitor off and back on, ...still no video signal to the monitor. (2) - cmds tried after disabling SIP: sudo nvram boot-args="niog=1" sudo nvram -d boot-args (when above cmd did not change issue) (3) - Yes reset NVRAM with keyboard keys during reboot (4) - 256MB GT Commented Aug 9, 2019 at 21:36
  • More cmds tried so far: sudo nvram boot-args="iog=0x0" sudo nvram boot-args=niog=1 (same as earlier reply but without quote marks: "niog=1" Commented Aug 9, 2019 at 21:38
  • Additional cmds tried, based on an earlier AskDifferent post: To reset the external monitor settings: remove the Folder ~/Library/Preferences/ByHost/ Followed all the instructions in an Apple Support article regarding how to correctly enable an external monitor to MBP's similar to mine: use external power for MBP, config settings in SysPrefs ...etc. I have not tried using the app some have suggested DisableMonitor, mostly because there is a comment on GitHub that it might cause damage to the MBP system, maybe corrupt an internal setting that is hard to restore (?). Commented Aug 9, 2019 at 21:54

1 Answer 1


As a start I think we need to establish if you can get your display to work correctly while your MacBook Pro is in closed-clamshell mode. To do this, follow these steps:

  1. Connect a USB keyboard and mouse to your MBP (or pair a Bluetooth keyboard and mouse with your MBP)
  2. Connect your MBP to an AC power source
  3. Connect your Viewsonic display to your MBP
  4. After your MBP desktop appears on your Viewsonic display, close your MBP's lid
  5. If your display goes to sleep, press a key or click your mouse to wake it up

NOTE: If your Viewsonic display doesn't wake up, then disconnect the display and shut down your MBP. Now connect your display while your MBP is off and then switch the MBP on. After logging in close the lid. Remember to keep the external keyboard and mouse connected

  • Should have mentioned earlier that I am using an external USB keyboard and mouse with the MBP and it is connected to an AC power source. After bootup the external Viewsonic monitor (2560x1440) is displaying the MacOSX desktop and the internal display is on with active extended desktop space. Closing the lid causes the external Viewsonic monitor to lose video signal. No mouse movement or keyboard activity, or even power-cycling the Viewsonic monitor restores the video signal. Disconnecting the Viewsonic monitor, shutting down, reconnecting the monitor repeats the same outcome as before. Commented Aug 10, 2019 at 9:05
  • OK - so far there doesn't seem to be an answer to the problem of wanting to deactivate the MBP internal LCD display while using an external display attached (to a MBP of my era) that uses a full Display Port interface channel off the mini-DP instead of mini-DP to DVI external displays which do allow proper clam-shelling the MBP internal display. Can anyone tell if this is a MacOSX driver/software issue or a MBP display hardware issue ? My guess is driver software limitation. Commented Sep 23, 2019 at 20:46

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