LG 34um95 Ultrawide Monitor Not Waking During Boot on 2013 MP

HI,

I have a similar issue with the LG- 34UM95-P on a Mac pro 5.1 (Mid2010).

The computer has been running this monitor (LG- 34UM95-P) fine, after an original cinema display died. This monitor had no issues until recently.

I have recently added a SSD-hard drive to the setup. After reinstall of a new copy of Sierra 10.12.3, the monitor is not recognized at startup. I have a separate smaller display that allows booting (with the LG34UM95 switched off), and is recognized once the computer has booted up.

if you happen to own an Apple Thunderbolt Display , then run it with that LG. You are not going to get the LG by itself showing the start up progress bar.

I now use the LG 31MU97 connected by minidisplayport and it works fine by itself or with the Apple TB display.

I think the problem with the LG displays is the timing of when that display wants to get to sleep mode. No way around it other than put up with the boot to black screen and Desktop eventually shows or use with an apple TB display.

Lastly you could try a DisplayPort connection instead of thunderbolt.

Hi,

I have the same issue with this monitor using Thunderbolt on my Late 2013 6-core Mac Pro with D500 GPUs. I get no image displayed until I get past my FileVault login and it takes me to the desktop. I have to enter my password blind as nothing is displayed at all during the boot. This also prevents me from choosing boot drives, or allowing other users to unlock the FileVault. The issue also occurs during a safe boot, and booting into recovery mode. My Mac Pro is running Yosemite, however it hasn't fixed the issue. I have tried a PRAM and SMC reset, however it hasn't changed the issue over Thunderbolt.

I have contacted LG (which is of no use as their support is really terrible), and Apple who actually sent my issue to engineering. However, engineering was only able to assist me with getting the HDMI working again. To get HDMI working, they had me do a PRAM reset with it plugged in using HDMI. They were unable to get the Thunderbolt working though, as the monitor is not officially supported.

I have been unable to find anyway to make the Thunderbolt work correctly on this monitor. This is very disappointing as this monitor is advertised by LG as being supported by the new Mac Pro.

I have a similar issue. I share this monitor between other computers using HDMI and DisplayPort connections. Flipping to an active DP or HDMI connection works fine. I can switch to Thunderbolt and half the time it does not respond and the display goes to sleep mode. I usually have to power off monitor then power on and it will notice. Also, whoever put the input selection on a sub menu, not direct from circle selector should be fired. (Who cares about Reader mode?)

What are the chances that LG will provide a firmware fix or that Apple will support the monitor officially?

I have the same no screen issue when booting. LG 34UM95 + MacMini 2014 late with HDMI (never tried with Thunderbolt). Does anybody have solution?

I reinstalled 10.11.x (El Capitan) under the Recovery menu (OS reinstalled/ programs stayed), after that I did a fresh install too (totally recreated the Fusion Drive group, partition and I installed OS) and the boot screen problem stayed. After that I did two fresh installs with Windows 10 Pro and after that with 10.10.5 (Yosemite) and those are perfect. So the problem is with the El Capitan OS! I hope Apple will fix it soon, because I want to use the El Capitan!