Multiple Displays have problems with El Capitan

I don't know what is causing this. I guess I am lucky - or you are unlucky.

Since installing El Capitan I have used my rMBP with different external displays, either connected through HDMI or Thunderbolt, with or without adapters, with zero issues. I have used it in my office at work, in my home office, in the living room, in my bedroom, in lectures connected to projectors. In some of those I used it while mirroring the display, in others as extended desktop. The OS remembers this, as well the relative positions of the displays.

I had not, however, used two external displays at the same time. So I loaned my colleague's monitor, and attached it, as well a 21.5" iMac.

All three displays worked fine together, and I can rearrange their locations at will.

I have an iMac with a second larger LED Cinema display. The menu bar is at the top of the larger display and I use that as the primary screen. When I power up with El Capitan both displays come up as normal but within a short time the 2nd display goes blank. I am now on 10.11.1 Beta (15B38b) and the problem persists. I have reported it through the Apple Feedback Assistant.

Oddly, if I take a screen shot of both displays (Shift+Command+3) the screenshot of the blank display is captured normally. That is, the OS thinks it is displaying the screen even when the physical display is blank.

I have found a workaround for now.

Power off iMac.

Cut power to 2nd display

Disconnect mini display port and USB connectors from back of iMac

Power up iMac and let it start up as a single-display system

When everything has loaded, plug external display into back of iMac

Apply power to 2nd display.

The system will then reconfigure itself with two displays and behave normally from then on. You just can't boot the whole system up with the second display connected.

This technique worked for me with my Philips external monitor running from a Macbook 5,2 (2009) (using mini dvi port to HDMI connector, then into the DVI input of the monitor). Seems to also work now even when booting with second display connected. Thanks for the tip.

Thanks for the tip!

It is just absolutely ridiculous that it;s hidden. I mean what's the point?

I had this problem as well. Resetting SMC and PMC and all that jazz did nothing. What worked, however was unplugging the display's power cable and plugging it back in after 15 seconds. This had been driving me nuts for days and that simple fix worked.

I have just updated to 10.11.1 from yosemite, and now my secondary monitor does not work at all.

none of the tricks listed here fix the issue. curiously, on yosemite, i had to power off/on the monitor on startup / after wake, but it did work. now, nothing i do fixes it.

I have a brand new Mac mini with two external monitors. I would like to have the screen span across the monitors. When I turn off the "each monitor" has it own space setting I get a blank screen on the second monitor.

mharelick wrote:

I have a brand new Mac mini with two external monitors. I would like to have the screen span across the monitors. When I turn off the "each monitor" has it own space setting I get a blank screen on the second monitor.

First let me see if I understand correctly, you turn "Displays have separate Spaces" OFF, then log out and log in again, and lose the second display? Is that it?

I can't reproduce it. For the first time in years I turned that setting off, logged out and back in, and the displays worked as expected (in my case that is a rMBP and an iMac as external display, in target display mode).

Do your displays still appear in System Information?

Did you try the Detect Displays button in System Preferences (as was noted in this thread, this button is now hidden, and only appears if you hold down the option key - whoever decided that was a good UI???)

I turn Display have Separate Spaces Off, logout and log in.

Then at first I see the display extended to both monitors.

When I try to maximize an application window so that it fills both displays the second display turns black and the application window is cut off at the boundary of the first window.

I am now on the latest beta version of El Capitan 10.11.1, released 10/23. The treatment of my second display has changed each week as the betas are released. Currently the situation is that if I try to boot up my iMac with the LED Cinema Display powered, the system will come up in the iMac only and will keep the second display dark.

Note that if I take a screenshot of both displays (Shift+Command+3) then the system captures the image that the OS thinks is showing on the 2nd display. But that display is in fact dark.

I have discovered that if I wait about 30 minutes after bringing the system up, and only then apply power to the second display, it will come on and behave almost normally. I say 'almost' as the screen brightness is dimmed and cannot be increased. Still better than not having the display at all.

This makes no sense at all. I realize that. But it is now my makeshift way of using El Capitan with two displays. Presumably there will be a new beta tomorrow that changes everything around again in some unexpected way.

What is your mac model? How is the display connected to your mac?

Did you have a chance to try it with a different display?

I have used several external displays with my rMBP in El Capitan - VGA monitors, VGA projectors, HDMI monitors, 1 HDMI TV, and an iMac in target display mode via Thunderbolt. Zero display issues, even with two external displays simultaneously.

I have to wonder what is different in your system. I would start with the display and cables.

One other thing that may cause problems is software. Did you try a clean install on a separate partition or external drive and see how that goes?

Most (but certainly not all) problems with El Capitan end up being caused by old software, bad caches and drivers, as a result of upgrading, so a clean install sometimes is the way to go.

Similar issue. Updated to El Cap earlier this week. Today after lunch the finder crashed hard and the display never came online. Have tried the reset, unplug, etc, etc, etc. Disappointed and now working on a 196 page catalog on the built-in display - unfun.

Machine is Mac Mini (Late 2014)

OS is 10.11.1 OS X El Capitan

When I initially reported this problem I had two dvi displays connected to each thunderbolt port via mini display to dvi adapters.

Now I have two thunderbolt monitors each connected to a different thunderbolt port. \

The effect I am having is that when I look at both screens they look like a full desktop. I can move windows objects around them and even put a window so that

its split by the monitors. When I click on the green button in the top left of the screen to make a window full screen, the secondary display turns black. This works with safari or any screen.

In Yosemite I was able to make a window go full screen across the two displays. That functionality appears broken in El Capitan.

I bought this machine 4 days ago and initially installed El Capitan before doing anything else. There has not been a history of usage of this machine before that.

I also just tried it with two thunderbolt displays daisy chained together going through a single thunderbolt port. Same result. With safari I can manually resize it by pulling at the corners so that it expands across both screens. However some applications do not support that kind of resizing and require the full screen mode. In particular remote desktop which I have to use.