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I have a notebook with a 7th gen i7 processor (Kaby Lake) and I use a setup with two external monitors, one is connected via HDMI, the other via Display Port.

This used to work fine until two weeks ago (I guess it was a kernel update). Now one of the screens randomly turns off and on again, sometimes 10 times in a row. Sometimes it's the HDMI screen, sometimes it's the Displayport screen. Sometimes the issue goes away when I unplug one of the monitors, sometimes it doesn't. Completely random.

And there's nothing in the system logs (/var/log/syslog).

Also in dmesg there are not graphics-related messages, only wifi.

The kernel I use at the moment is 4.10.0-38-generic #42~16.04.1-Ubuntu SMP

What can I do to diagnose this problem?

closed as off-topic by Bastian Voigt, karel, Eric Carvalho, Thomas Ward Oct 17 '18 at 14:47

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This describes a problem that can't be reproduced, that seemingly went away on its own or was only relevant to a very specific period of time. It's off-topic as it's unlikely to help future readers." – karel, Thomas Ward
If this question can be reworded to fit the rules in the help center, please edit the question.

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    My docking station does this and is a 5th generation m7. Does it eventually stay up? Mine eventually sticks after about 20 seconds. Also, have you discounted the cable? I've had some really dodgy HDMI cables create this kind of problem over the years also. And finally, have you booted into an earlier kernel to isolate the kernel version where the problem first appears? Unless you've run autoremove, the earlier kernel versions will still be in yout Grub Boot menu. :-) – tudor Oct 8 '18 at 10:22
  • P.S. Nice Beatles reference. lol. ;-) – tudor Oct 8 '18 at 10:22
  • Please ping me @Fabby after you've responded to Tudor, please, because it looks like a dodgy cable or connector to me too... – Fabby Oct 8 '18 at 15:11
  • You are right, it was the HDMI cable :( Would never have thought this, because the problem appeared so suddently after a kernel upgrade. I am going to delete this question because I believe it is not much help for other people having similar problems :) Thanks for all the suggestions! – Bastian Voigt Oct 12 '18 at 6:58
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Kernel version 4.10.0-38 was released for Ubuntu 16.04: https://packages.ubuntu.com/xenial-updates/linux-image-4.10.0-38-generic

Because you are using Ubuntu 18.04 I'd recommend trying most recent Kernel version 4.15 designed for Ubuntu 18.04. If you have a problem witht hat kernel version you can try mainline kernel 4.14.74 or 4.18.12 instead.

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From the OP's comments:

You are right, it was the HDMI cable :( Would never have thought this, because the problem appeared so suddently after a kernel upgrade. I am going to delete this question because I believe it is not much help for other people having similar problems :) Thanks for all the suggestions!

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