El Capitan does not detect my external display

I have the identical problem. MacBook Pro (Retina, 15-inch, Mid 2014), external Dell display. Before El Capitan (10.11) it was detected reliably.

I tried:

- Manual "Detect Displays" in Settings does not detect it either.

- Power cycle monitor

- Use HDMI vs Thunderbolt

- Reboot

I found that I have the identical problem with a projector in a conference room, thus it doesn't appear to be Dell specific. Any help would be highly appreciated.

Guido

Edit: There are numerous bug reports in other forums of the same issue, but no resolution yet.

I was able to resolve the issue with an SMC reset (see Resetting the System Management Controller (SMC) on your Mac - Apple Support). Display appears to be now detected reliably.

I'm having the same issue with an Optoma DLP projector connected via DVI and S-video cable to an iMac. Resetting SMC didn't help. Hope someone comes up with a fix soon

Same problem here with a MacPro and two identical Samsung monitors. After resetting SMC, the right monitor no longer displays but the left one, which previously wasn't displaying, now does. Bad bug for sure. Please fix, Apple. Hard to believe this wasn't tested prior to release.

I have a MacBook aluminum which still works just fine. However, since installing El Capitan, I cannot get the video adapter to detect external displays of any kind. The firmware update to the adapter doesn't apply to El Cap (not yet, anyway). I've reset the SMC. No change. Any ideas? Could the adapter itself be toast? It's as old as the computer. I got them at the same time.

Just spoken to Apple Support and its an issue Apple are aware of and are currently investigating and attempting to solve. They do not have a specific date it will be fixed however in the mean time, if you restart your MacBook whilst connected to the external display then that will temporarily fix the issue.

Thanks. I tried that just now. No deal. When I plug in the adapter, the external screen goes dark but that's it. That's for each of my two external displays. Neither have done that before.

I upgraded my Mac Pro 2013 to El Capitan and only one of my two identical displays would work. One display uses a mini-display port converter and the other HDMI. This was a problem when the Mac Pro was first released, but improved with Yosemite. I tried resetting SMS, NVRAM but no joy. I also have a thunderbolt external raid array connected. When I disconnected the thunderbolt array and rebooted the Mac Pro, both displays appeared. The miniDP is NOT on the same thunderbolt bus as the raid array. The problem appears to be an issue between the thunderbolt and miniDP during startup. When I started the array after boot up, both displays work fine.

Not applicable to the MacBookpro, but may be helpful for (the dwindling number) Mac Pro users.

Me too. SMC saved my ***.

I have a MacBook Air with a 13" screen (early 2015) running El Capitan 10.11.1, and I tried to hook it up to a projector for a presentation, but it wouldn't recognize the projector at all (which was a huge problem given that I was about to give a presentation with it). It had previously worked with the exact same projector when I had Yosemite installed.

Since part of the purpose of having the MacBook is for presentations, I really need to find a solution as soon as possible.

I found a solution for my Dell external display connected via Mini-DisplayPort-to-DisplayPort. The problem/solution spans both Yosemite and El Capitan, so I answered in the Yosemite thread.

Long story short: if you use DisplayPort to connect your external monitor, it really might be the cable (I know, I know. I resisted the idea as well because it made no sense for a cable that had been working perfectly fine for over a year to suddenly stop working coincident with an OS update).

Here is the link to my post on the Yosemite thread, which contains details: Re: Yosemite does not recognize external displays...

I also found the issue to be the cable, specifically the Mini display port to VGA converter.

When I swapped out the converter for another brand, my external monitor again was working fine.

The adapter that did not work with my Mac Mini and El Capitan does work fine on another laptop running Windows 8.1. So the adapter is not faulty.

The issue I had looks like it was introduced by El Capitan, and affects DisplayPort to VGA adapters. I tries the SMC/NVRAM reset steps, these did not resolved me issue.

Same issue for me, and the SMC suggestion does not fix it. Hopefully Apple will get the fix out soon. Connecting to a VGA device is a pretty basic function....

See peterfromnm's EDIT: Striinger's and my post above. Apple may never put out a fix because they may not see this as a case of anything being broken. Frustrating, yes, but typical.

The list of certified VESA compliant cables and adapters for DisplayPort-to-[x] connectors is actually very short. You can look them up here:

http://www.displayport.org/products-database/?products_category%5b%5d=cables-con nectors&products_manufacturer=

If your current adapter or cable is not on the above database, I'd start with replacing it with one that is. I'm sure ones not on this list may work, but instead of trying lots of different cables, best to just pick one you know is certified compliant to save time, since these sorts of cables and adapters usually have to be ordered online.

I had a similar problem. I have a new 15" MacBook Pro with El Capitan. I did reset the SMC and nothing changed. I disabled the user login and everything works perfectly now.