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My dad has a Mac Pro (2009 era) and runs 3 monitors hooked up with DisplayPort. They are not high-res and only about 24". Nothing that a Mac Pro should have any issues with. Everything worked well until he upgraded to El Capitan last week. Almost immediately, it crashed to the login screen. I spent a while troubleshooting the problem and all of the crash reports point to graphics problems (which seems apparent). Right now, he is down to one monitor to mostly rule out the crashes. I found that disabling "each display on it's own space" helped, but if he is working with one display and a notification comes in on the other one, it will consistently crash.

I'm not sure what else to try. Is there a way that we could get him back up to the three monitors? I understand that these problems could point a potential graphics card problem, but I don't think that is the problem considering the direct correlation to the OS upgrade and the crashing. I also haven't been able to find others with similar problems.

I have tried:

  • Multiple Reboots
  • Disable: "Preferences -> Mission Control -> Displays have separate Spaces"
  • Disable: "Preferences -> Mission Control -> Automatically rearrange Spaces based on most recent use"
  • Confirm that "Automatic Graphics Switching" didn't exist on his machine
  • More reboots
  • I encountered this exact same problem today (2009 Mac Pro, 2x 24" displays via DisplayPort). I'll try these steps when I'm back in my office. If you disable notifications, does that prevent the crashes? – user151392 Oct 9 '15 at 3:23
  • @MarkB., it sounds like you have an identical setup which makes me think that El Capitan just doesn't like that particular graphics card or something along those lines. Disabling notifications is a great idea as that would prevent it from switching displays on its own. The next question is whether changing focus from screen to screen would crash it, but I tested that and don't think it's the case. – bassplayer7 Oct 9 '15 at 10:46
  • I'm seeing the same problem. I have an early 2009 Mac Pro with twin monitors connected with DVI connectors. Frequent crash behaviour to log in screen. I have 2 x NVIDIA GeForce GT 120 in the machine. – swervo Oct 11 '15 at 19:51
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This problem is well documented on the Apple forums. For the moment, until the next release of El Capitan, you can only run two monitors. The monitors must be connected to one video card. You do not have to remove the other card.

Please search the Apple forums for more details.

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Upgrading Graphics Card didn't work for me, I have an Early 2009 Mac Pro running the latest version of El Capitan and the only monitor that will work for me is my 2004 Apple Cinema Display that uses DVI or screw in cable (not mini DisplayPort) For some reason My 24" Apple LED Cinema Display will not stay on. It goes black but if I shine a light into the display I see that it still has a picture but no backlighting. When I initially plug it into the Mac Pro it flickers but doesn't stay on. Even when it's plugged in my itself or duel with two monitors and every single time the 2004 monitor lights up great and works. What is going on with Apple and El Capitan and the compatibility with Mini DisplayPort and Cinema Displays. For me it didn't seem to matter whether it was one or two monitors the LED display just won't fire.

You could try an SMC reset and reset the ParameterRAM or Pram. Those things seem to help some people. (not me in my case)

What did seem to help temporarily until I shutdown. (Just leave your computer on if it works!!! Until Apple has an El Capitan update.

  1. Shut Down computer it it's not already shut down
  2. Unplug all peripherals and computer for 30 seconds
  3. Plug in computer to power and one monitor
  4. Start-up and check to see if monitor is working
  5. If monitor is working, then plug in second and then third display and restart

Good Luck, hope Apple soon fixes this issue. I really like my 24" LED Cinema Display and it's sad that I have to use my 2004 model on my early 2009 Mac Pro that is still VERY NICE!

  • What you described doesn't sound a problem with Mac or OS X. It sounds like the backlight on your LED Cinema display is faulty. – Allan Jun 29 '16 at 20:13
  • Yes, after hours of relentless troubleshooting it turned out to be a faulty Apple LED Cinema Display. – Kenny Aug 18 '16 at 3:19
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Update:

An OS 10.11.x update fixed the problem. If you are still experiencing this problem, make sure that you are on at least OS 10.11.3


He was able to get an improvement (but not a fix) by resetting the NVRAM on his Mac Pro. He still experiences a number of crashes throughout the day, but at least he is running all three monitors and is still able to work somewhat efficiently.

He was unable to install the drivers recommended by @Stig, even though they did look somewhat promising.

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New drivers released from Nvidia for El Capitan:

Quadro & GeForce MAC OS X driver release 346.03.02

  • Has anyone tried this? And why has it been down-voted given that it seems to address the problem directly. – swervo Oct 28 '15 at 14:17

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