[SOLVED] All three displays work with one user, but only two work with another!

[steveharman]

Hi,

I just upgraded from Sierra > High Sierra on my Gigabyte H170N (4GHZ Intel Core i7). The Sierra install was flawless for about a year previous and indeed I'm now up and running on High Sierra ok as well, except for one slightly bizarre thing that I can't get my head around

My motherboard has onboard Intel HD 530 (DVI out) and a PCI Nvidia GeForce GTX 650 (dual DVI out) - a total of three displays.

After doing a fresh High Sierra install (not an upgrade) I ran Multibeast with known-good config options, restored my single admin user from a Time Machine backup and logged in. So far so good, except for some reason only two of the three displays show output. One of the displays connected to one of the outputs of the GTX 650 just displays a black screen.

Now for the weird parts:

(a) To debug this I created a new admin user, logged in as them and all three displays work fine! No need to reboot or anything - simply Apple Menu > Logout of the original user where the display is black, login to the new admin user and hey presto all three screens show content perfectly ok.

(b) The "black" screen is actually up & running as far as System Information > Graphics/Displays and System Preferences > Displays > Arrangement is concerned. I can drag windows from my main display on to the "dark" one. It's not as if there's no display recognised whereby my mouse cursor would reach the edge of the main display and stop going any further. I can mouse-over to the dark display, drag files on to its hidden desktop, click its icon in System Preferences > Displays > Arrangement. It's just black. Unless I login as my second user, in which case it works fine.​

Surely this can't be a config.plist or video injection issue if all the GTX 650 outputs work fine for one user but not another? I'm stumped - does anyone have any ideas of what I can try? It's almost as if my original "Time Machine Restored" user brought back some corrupt config file perhaps?

Thanks,

Steve

 

[steveharman]

As suspected, this was more to do with a configuration file belonging to my original user than it was the hardware config of the system. The following worked for me:

From Terminal remove the windowserver preference files using the following commands:

rm /Library/Preferences/com.apple.windowserver.plist

rm /Users/[username]/Library/Preferences/ByHost/com.apple.windowserver.*

After a system restart nothing seemed to change, in fact now only one monitor worked (IGFX). But after visiting System Preferences > Displays and turning Mirror Displays off (no idea why it was on....) all three displays bust into life as normal.

I can't be 100% sure it was the Mirror Displays step on its own which made the difference, although I didn't want it on anyway, as I'd changed a few settings (Colours & Arrangement) in Displays as well, but toggling Mirror Displays off was the step which appeared to make the difference.

HTH someone

Steve