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new to Kubuntu and relatively new to Linux overall. I installed Kubuntu 16.04 on Desktop with add-on Radeon HD 5850 GPU. I'd previously used this exact hardware to run dual monitor. I plug a DVI (my main monitor) in and an HDMI that runs to a HD TV in another room. When I installed 16.04 the setup worked perfectly. All I had to do was switch Audio Configuration to change sound from one to the other. Yesterday I updated the system and suddenly, when the desktop is on the TV is black. So I tried to change the configuration with the GUI Display Configuration Utility but could not fix it. If I leave the HDMI plugged in the Display configuration shows that both are recognized, but only one screen can be seen at a time. Unplugging HDMI brings the regular monitor back, plugging the HDMI in switches the output to the TV. When I login, I can see the dual screen on both until I finish the boot, then it starts this behavior.

  • To add a little more detail. If I plug both DVI Monitor and HDMI plugs into the GPU before booting, I can see both at the login screen. That is both are duplicated which is what I want. Then I put my password in and the OS loading bar starts to cross. As soon as it gets to about 75% loaded the DVI monitor suddenly goes black and says "No Signal" I can still see it on the TV in the other room. – muttony Jul 8 '16 at 19:55
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I have a similar setup, different gpu version and using VGA and DVI. I am facing the same problem from the most recent update. I previously had both monitors working with the 4.4.0.22 kernel.

During startup see if there is a new kernel installed and try booting into an older one.

How to change kernel at boot

edit: also try this Dell 3543 Kubuntu 16.04 can't get output to 2nd monitor on HDMI i haven't had a chance to give this solution a go

  • Changing the Kernel back had no effect. – muttony Jul 8 '16 at 19:31
  • the fix on the Dell 3543 thread didn't work either. – muttony Jul 8 '16 at 19:52

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