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I have a desktop running vanilla ubuntu 16.04 with 4 monitors at work. Its always been a bit buggy with starting all 4 monitors, but after holidays its gotten worse. Normally I just reboot or turn monitor in question on-off a few times and its gets it in 2-3 trys.

2 monitors (the left 2 in pic) where unplugged for holidays. This is the only thing that changed. PC was off for 3 weeks. Problem started before I did any updates. Updates now caught up. problem persists.

Now the far left one only works in grub. Once I get to log in screen it drops out. I've rebooted and switched monitor off and on a bunch of times. Its not getting detected.

Don't have a spare DP-HDMI cable to try, but did try changing ports on the monitor (which is actually a TV with 2 hdmi inputs) and the RX580. Same results. So I don't think its the cable which is quite new and plugged in firmly (this has been a problem in past with HDMI which is why I tripple and double checked its in firmly).

I did however swap the HDMI with the monitor running on HDMI port. This does swap which monitor works. I have tried DP-1&2 Results are the same.

When I turn PC on it shows Bios and Grub on the TV connected to Display Port 1 and on the monitor connected to DVI-1. Then as soon as grub closes the DP-1 monitor drops out and the others all come on.

It has never displayed BIOS or grub on all the monitors, usually 1-2 monitors and often changes which ones each boot. I don't care about this, as long as one comes on so I can chose a grub option in the rare event I need to....

One last thing to mention is the tv/monitor had over-scanning problem. So I gave it custom resolution. For a while I was doing this every boot, via xrandr, then I eventually edited a startup file to include the new resolution, sorry I cant remember which file it was, can probably google up instructions I followed if needed. I don't think this is related though. Except its still showing the custom resolution for DP-1...

I've rebooted about 20 times now its not even looking like working after ubuntu starts.

Here is my xrander output:

    :~$ xrandr
Screen 0: minimum 320 x 200, current 4480 x 1080, maximum 16384 x 16384
DisplayPort-0 connected primary 1280x1024+3200+0 (normal left inverted right x axis y axis) 376mm x 301mm
   1280x1024     60.02*+  75.02  
   1280x800      60.02  
   1152x864      75.00  
   1280x720      60.02  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   640x480       75.00    59.94  
   720x400       70.08  
DisplayPort-1 disconnected (normal left inverted right x axis y axis)
   1800x1012_60.00  60.00  
DisplayPort-2 disconnected (normal left inverted right x axis y axis)
HDMI-A-0 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 477mm x 268mm
   1920x1080     60.00*+  60.00    50.00    59.94  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1440x900      74.98    59.90  
   1280x960      60.00  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1152x720      59.97  
   1024x768      75.03    60.00  
   832x624       74.55  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
   1800x1012_60.00  60.00  
DVI-D-0 connected 1280x1024+1920+0 (normal left inverted right x axis y axis) 376mm x 301mm
   1280x1024     60.02*+  75.02  
   1280x800      60.02  
   1152x864      75.00  
   1280x720      60.02  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   640x480       75.00    59.94  
   720x400       70.08  

Grub works Please excuse desk mess, been digging for cables etc.

After booting Ubuntu Monitor not working

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Nevermind.

Reading through my post I'm thinking: This really sounds like a cable problem.

Unplugged the cable from port in GPU and plugged it back in really really hard. For the 10th time today. Blank monitor lit up. Everything works.

Still mystified as to why Bios and Grub would work though? And why it suddenly had preference for the bad cable?? Maybe because lower resolution on those screens?

I'll get spare cables when I get a chance. Suspect this one only good for a few more moves.

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  • +1 for good troubleshooting: "Have I really eliminated this possible cause? I thought so, but let's double-check that." I think you just saved yourself weeks of frustration. – user535733 Jan 13 '20 at 0:19
  • Weeks of frustration and a $40 cable I don't have the cash to buy for a while. :D – MongrelShark Jan 13 '20 at 2:18

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