External monitor OS bug - Black Screen with cursor

There seems to be a nasty bug in the new El Capitan OSx with external monitors on my iMac 5k retina.

External monitor connected causes both monitors to show black screen with cursor at the point where the login would normally appear.

1. OS X Yosemite works fine and does not have this issue.

2. Upgrade to OS X El Capitan has this issue. Disconnect ext monitor boot again and its fine.

3. Clean install El Capitan on iMac from wiped partition and issue shows if ext monitor connected.

4. Restore Yosemite from time machine or install clean and issue does not happen.

5. Try several different monitors and same issue. Each connected by an original apple Thunderbolt to HDMI cable.

6. Each of these monitors work perfectly if booted under Yosemite on same machine.

7.If they are connected after login they then work fine, but if logged out, the issue shows again.

8. If monitor is disconnected before logout, then the issue does not show and the normal login shows.

No matter what i do, upgrade or clean install this is happening every time on El Capitan.

Hopefully someone at Apple will see this and acknowlege the issue or supply a workaround other than connecting and disconnecting the monitor.

iMac with Retina 5K display, OS X El Capitan (10.11), Core i7, 32GB, 1TB SSD

Posted on Oct 4, 2015 4:42 PM

18 replies

TheOasis

Level 1

4 points

Jul 12, 2016 12:07 PM in response to franciscofrombaltimore

Same problem! Only my problem occurred AFTER I upgraded my iMac from a spindle drive to SSD.

1. Boot with El Capitan

2. After Mac logo, grey screen and mouse cursor

3. Pull displayport on external monitor and login screen appears as desired.

4. Put displayport back in

5. Login and all good.

Oct 17, 2016 10:07 AM in response to nicwilson58

I have this same issue on Mavericks - external monitor works, then at some point after waking from sleep it will work for 5 seconds or so then go solid black and only my mouse cursor is visible. Dragging a window onto it from the laptop only shows the mouse cursor, as well. Restarting the monitor very rarely corrects it - it usually just works for 5 seconds and goes black again.

Temporarily turning on mirror displays has been a more reliable fix. It screws with window arrangement, but gets me past the black screen at least.

Feb 21, 2017 7:54 AM in response to bdichiara

As I suspected. I rebooted and both external displays are working again (with the exception of the one flickering, DELL ST2410 Display, Thunderbolt to HDMI cable).

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External monitor OS bug - Black Screen with cursor