External HDMI monitor detected but says "No signal" on Fedora 26 Macbook Pro

edit

Hello,

I'm running fedora 26 running on a Macbook pro 2011. I've connected an external monitor via a Mini DisplayPort to HDMI converter that is connected to the laptop. When I start up the laptop, the splash screen shows up on both the laptop and the external screen so I know for sure that the external screen works. However, after booting, it doesn't show any more picture. The HDMI device seems to be detected by xrandr but the screen continues to say "No Signal".

Output of uname:

~  uname  -a
Linux localhost.localdomain 4.11.10-300.fc26.x86_64 #1 SMP Wed Jul 12 17:05:39 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Output of xrandr:

~  xrandr
Screen 0: minimum 320 x 200, current 2720 x 900, maximum 8192 x 8192
LVDS-2 connected primary 1440x900+0+0 (normal left inverted right x axis y axis) 331mm x 207mm
   1440x900      59.90*+
   1024x768      60.04    60.00  
   960x720       60.00  
   928x696       60.05  
   896x672       60.01  
   800x600       60.00    60.32    56.25  
   700x525       59.98  
   640x512       60.02  
   640x480       60.00    59.94  
   512x384       60.00  
   400x300       60.32    56.34  
   320x240       60.05  
VGA-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 connected 1280x720+1440+0 (normal left inverted right x axis y axis) 1150mm x 648mm
   1280x720      60.32*+  60.00    50.00    50.00    59.94  
   1920x1080     60.00    50.00    59.94  
   1920x1080i    60.00    50.00    59.94  
   2880x576i     50.00  
   1280x1024     75.02  
   1024x768      75.03    70.07    60.00  
   1440x480      60.00    59.94  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   720x480i      60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.95    59.94  
   720x400       70.08  
DP-4 disconnected (normal left inverted right x axis y axis)

Output of lspci:

~  lspci
00:00.0 Host bridge: Intel Corporation 2nd Generation Core Processor Family DRAM Controller (rev 09)
00:01.0 PCI bridge: Intel Corporation Xeon E3-1200/2nd Generation Core Processor Family PCI Express Root Port (rev 09)
00:01.1 PCI bridge: Intel Corporation Xeon E3-1200/2nd Generation Core Processor Family PCI Express Root Port (rev 09)
00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
00:16.0 Communication controller: Intel Corporation 6 Series/C200 Series Chipset Family MEI Controller #1 (rev 04)
00:1a.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Universal Host Controller #5 (rev 05)
00:1a.7 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #2 (rev 05)
00:1b.0 Audio device: Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller (rev 05)
00:1c.0 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 1 (rev b5)
00:1c.1 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset ...