Multiple Displays have problems with El Capitan

I was having this problem too. Just upgraded to 10.11.2. I suppose I have no business expecting my old Mac Mini Late 2009 to handle this new OS but I've seen others handle it. I kept OS 10.6.8 on a separate partition because I don't have nearly the money necessary to upgrade all my older software.

The Mac looked like it knew the second monitor was supposed to be there, old windows opened up there, the orientation was correct but the monitor stayed in standby mode, whether during a startup or a restart. Primary: VGA to Mini DVI via adapter, Secondary: VGA to Mini Display port via adapter. "Displays have separate spaces" checked. "Detect Displays" did not work. Powering the monitor on and then off, nothing. The only way I could get the second monitor to work was to unplug and replug that secondary monitor after startup. Also, just disconnecting the VGA plug from the VGA to Mini Display adapter was not sufficient, I had to unplug the adapter from the Mac and then replug it.

After a Command-Option-P-R the problem sorta solved itself...but I ended up with a different problem: The Mac now prefers to startup under the older OS, even if I had last used the newer one. Once it starts under 10.6.8, both monitors once again work automatically. But when I try to restart via "Startup Disc" at System Preferences the newer OS does not show up. I have to do a restart holding down the Option key in order to select the new OS. Why would the Mac all-of-a-sudden be sorta-kinda-blind to the newer OS partition?

Release 10.11.3 seems to finally have saved this issue, so for sure a recommended update!!

/Mats/

Unfortunately I cannot confirm: after updating to 10.11.3 still both screens black after reboot: Solution, unplug external display until login stage. I was hopeful too, but sorry Apple: problem not solved, back to Os programming department. My Hardware: MBP 15"mid 2015, retina External monitor HP EliteDisplay E2411.

In the meantime I'm used to it. >;-) Monitor works perfect past booting. Everything was fine until El Capitan. ah well........

Thomas :-)

I reset the NVRAM and now it's not as easy to simply start in 10.11.2. WIll the new update fix that?

Thanks a lot. Your workaround finally helped :-)

I was having the problem with only one monitor showing up, and boot up was taking an unusually long time. The solution for me proved to be unplugging all peripherals except the monitors and adding them back one-by-one. When I connected a card reader the problem resurfaced. I even verified this as I replicated the problem on a different machine. All is well now.

This was what killed it for me and El Capitan. I made the jump and lost my extra Acer monitor. Then I would login and within about 30 seconds, often less, it would boot me back out to the login screen. Over and over and over again. I wasted days on trying to solve the problem.

So I had to revert to Yosemite. Back "in the day" you could get old versions of the OS for just such a problem, but that isn't the case now as far as I can tell. Fortunately I had a copy somehow laying around. I reverted and solved all problems. The moral: No upgrade goes unpunished. It seems like especially since Steve Jobs anal attention to detail has left the building. Oh and when you download an OS install, back it up someplace in case you need it.

I had the same problem, this might work:

Have had issues with external monitor not being recognized, MacBook Pro 2015/ El Capitan. Thought it was due to upgrade. Tried hitting option key under display preferences, Tried multiple resets. Tried SMC reset. Fixed problem by recognizing mini adaptor (thunderbolt) was upside down, and it works if you insert it with small logo on top. Yes, It can go in both ways. If you have this problem, unplug the thunderbolt plug from the mac, look at it and reverse it, try again. JG

I was having a similar problem. 2013 Mac Pro with two Cinema 30" Displays. I had been using El Capitan without issue for a few weeks and then one day after a routine reboot, only one display would come up - the other would be completely non-powered. Swapping the display connectors proved that the displays were ok - but somehow both were not being recognized at the same time..

Solution: Shutdown computer and disconnect all external drives and other peripherals except for keyboard and 1 monitor. Restart. System should come up normally. Connect second monitor to the open display port - it should fire up normally. Add each external drive and peripheral one by one until all are connected.

So far this solution is working fine and doesn't need to be done between subsequent restarts.

i am running a 2008 8 core 3.1 MP with two Nvidia GT120 graphics. Early EC crashed, crashed, crashed. I waited and waited. Now NVIDIA has new drivers for version 10.11.3. They work. System now is acting stable with 4 monitors You must upgrade El Capitan first, then install the drivers from NVIDIA. I downloaded them first and unplugged all but one monitor from the graphics cards. Installed 10.11.3, then the drivers, then reboot, then added monitors. First to existing plug in card, then to other card. So far so good. I did not do any system resets.

Dan's solution did not work for me. Does my NVIDIA GeForce 9400 need new drivers???

Since resetting the NVRAM I can no longer automatically start under 10.11. That partition no longer shows up under Startup Disc in System Preferences. I can only get there by the Option button route. If I remember upon startup the second monitor is not recognized (I have to do the unplug-replug routine). If I do this on restart both monitors work immediately. After getting to 10.11 (which I must do seeing as the newer OS means a newer Itunes which means it processed the library files such that 10.6.8 no longer works with them) any further startup just revert back to the older OS. Why doesn't the Mac "see" the newer OS unless forced there?

The primary monitor goes through a KVM. It's the secondary that goes directly to the Mac but the new os doesn't see it, so I doubt I can blame the KVM.

Hi Soren, have you managed to find a resolution to your issue as I suffer exactly the same issue since upgrading.

Cheers

Had to abandon El Capitan and only go to that partition when I need to. Had to entirely regenerate my Itunes library, but gained back my extra monitor.

They need to get a resolution to this asap - as its a bit of a job going back to Yosemite.

Did doing that 100% fix all your display issues?

Thanks millport. After many straggle, your solution works great!! Thanks again.