Multiple Displays have problems with El Capitan

Thanks for this tip Millport.

I have an old 20" cinema display and a new 21" imac. Connection is via an adapter to thunderbolt. The cinema was working fine for a while; once or twice the system did not recognize it, but rebooting fixed this. New development as of last week was total non-recognition, eg in the system profile it showed nothing connected to thunderbolt. I tried a bunch of fixes gathered from here and there, but this one was the one that finally worked.

Cheers for that!! Worked a treat. Much obliged.

I was having the same problem - slow startup and only one monitor working when I upgraded to El Capitan. Disconnected everything except my main monitor an keyboard and immediately noticed the much faster startup. I added second monitor and restarted. Still fast, both monitors worked. Added thunderbolt doc with other peripherals connected, still worked. Finally added an external usb drive and it went back to slow startup and one monitor. Unplugged it and everything worked again. Yeah, I finally have my monitors back. I even added a third monitor in my HDMI port and it still works. Love being back at my 20 second startup vs minute plus. Thanks BereaVideo!!

Mac Pro Quad 3.7 Ghz, 16 GB, 512 GB

Hi Luis.

I have a Mac Book Air, with El Capitan 10.11.5 beta (15F31a), today I I bought a Monitor AOC model E2270Sw, and is imposible connect with my mac. I have tried all that you said, but the monitor indicate NO SIGNAL.

Can you help me?

Thanks in advance.

I used this workaround a few times but now I feel I have found a better one.

When I start up and get to the login screen, I can tell whether my external display is working (it shows a faint wallpaper, even though the login is on the main screen) or not (it shows nothing at all). If it is working, login and all is well. If not, restart without logging in, in safe mode (hold the shift key until the apple appears). In my setup, at least, this will cause the external monitor work on the subsequent startup. And in my case, running in safe mode does not cause any serious issues. However, if I want to get out of safe mode, another restart out of safe mode seems almost always to bring me to a login screen in which my external display is working.

Maurirostan wrote:

Hi Luis.

I have a Mac Book Air, with El Capitan 10.11.5 beta (15F31a), today I I bought a Monitor AOC model E2270Sw, and is imposible connect with my mac. I have tried all that you said, but the monitor indicate NO SIGNAL.

Can you help me?

Thanks in advance.

Does the Mac recognize that a monitor is connected? If you open System Preferences->Displays, do you see an "Arrangement" tab?

Or just Display and Color?

You can also look at System Information (option-click the Apple menu), in Displays.

If the mac "sees" the display, it may be sending a signal with a resolution and refresh rate that the display can't handle.

If the mac does not see the display, maybe the display is selecting a different input (e.g. VGA instead of HDMI, or HDMI instead of HDMI2); or maybe the cable is not well attached, or is faulty.

Just in case this helps anyone: I had exactly the same issue as reported by millport. It was particularly intriguing that I could get a screenshot of the external monitor but the monitor itself was blank. Over a few weeks I tried everything recommended in this discussion and as the problem coincided with a recent OS and RAM upgrade I was even contemplating reversing those but in the end it turned out to simply be crud in the thunderbolt socket (a small piece of paper to be exact). Always the obvious thing last 😊

If only i had such an easy issue Martin but glad your working; mine is a software issue i.e. EL Capitan as my TV knows theres an HDMI cable connected but the software cant detect it. Pathetic that apple cant fix this, other reason i know is it worked before upgrade then stopped after; nice of apple to pitch in to something they obviously cant fix - great way to loose customers considering the amount of posts on this matter and outputting to TV's is pretty important nowadays. Ive even went out and purchased a £70 cable to double check i wasn't being stupid and thats now confirmed, also dosent detect in another TV and 2 monitors ALL 4k capable so resolution should be no problem.

I love my IMac but the 5k one is off the shopping list for now since this effects all models as per the posts.

Can i say Microsoft support is not great but an issue like this would be fixed very quickly, does it matter the GPU chipset thats outputting to the TV/Moitor(s) noone ever seems to mention that and it could be Radeon/Nvidia or Intel (Yuk).

Does Detect Displays show you the display? Does the mac not notice the external display at all? Did you try the several steps suggested in this thread (safe mode, unplugging/replugging the cable after login)?

FWIW, although this is a long thread, many of the people posting seem to have gotten their problem solved one way or another; more importantly, there are many more users who carry on using external displays with their macs without issue, so it is not like "EC can't connect to a 4K tv" is a fact of life. It is not. I hope you get this sorted out and get to use your mac with the great 4K screen.

Agreed some people have managed to use lame workarounds and other good fixes to get it working (Im not being that guy just accepting having to reboot to get your display to work is not acceptable to me altho i'd take it too if that was the solution); altho no i've tried all and still no joy, just funny the TV knows the mac is there but the mac cant detect it even when forced to look, pretty disappointed in all as it worked on the previous OS so they should look at what they modified on the graphics side to cause such an issue. My imac is a 2010 model and still runs excellently except this flaw but it puts me off their over inflated priced hardware when they dont fix it - if they do i happily pay the extra for a hugely inferior spec machine because of the build quality.

Also just to expand this is a major issue with LOTS of people having this problem but i guess theres a new iphone to design. (I mean re-shape)

Waveform2 wrote:

Also just to expand this is a major issue with LOTS of people having this problem but i guess theres a new iphone to design. (I mean re-shape)

I haven't seen anything about this outside this thread. I use FCP X and have heard many video editors that use EC with 4K displays.

I wish I could test - I don't have a 4K display of any kind. I do use many different displays (projectors, monitor, tv) with my EC mac (a rMBP if it makes a difference).

I can't say how many people are affected, but as I wrote before I believe that something specific to people's systems is involved, rather than a OS bug outright - otherwise there would be a huge outcry.

Can you make a clean install of 10.11.5 on a separate disk, and try? I suspect that something else you have installed on your system may be behind the problem.

This has nothing specifically to do with 4k displays just output to an external display i shall do a clean install but since it worked before upgrade and i run a pretty clean systems except work software (acad/pshop) no crappy little apps i doubt it'll work but i'll be an optimist just to see. Cheers for the ideas btw im not a grumpy git all the time.

I have this exact same issue, but I'm on a Mac Mini. What's really odd is that in Boot Camp and the Recovery Partition, both monitors work perfectly, every single time. It's only OSX El Capitan that won't recognize the second monitor.

Going to try the SMC reset and see if it at least fixes my issue. Right now they're recommending I re-install OSX.