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I have a Dell XPS 14 with two HDMI outputs and two external monitors. I'm running 12.04, fully updated as of 2014-05-26. Here's what xrandr -q reports:

xps% xrandr -q
Screen 0: minimum 320 x 200, current 3072 x 1080, maximum 8192 x 8192
LVDS1 connected 1152x864+0+0 (normal left inverted right x axis y axis) 309mm x 174mm
   1600x900       60.0 +   40.0  
   1440x900       59.9  
   1360x768       59.8     60.0  
   1152x864       60.0* 
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected (normal left inverted right x axis y axis)
HDMI1 connected (normal left inverted right x axis y axis)
   1920x1080      60.0 +
   1600x1200      60.0  
   1680x1050      60.0  
   1400x1050      60.0  
   1280x1024      75.0     60.0  
   1440x900       59.9  
   1280x960       60.0  
   1152x864       75.0  
   1024x768       75.1     70.1     60.0  
   832x624        74.6  
   800x600        72.2     75.0     60.3     56.2  
   640x480        72.8     75.0     66.7     60.0  
   720x400        70.1  
DP1 disconnected (normal left inverted right x axis y axis)
HDMI2 connected 1920x1080+1152+0 (normal left inverted right x axis y axis) 520mm x 290mm
   1920x1080      60.0*+
   1600x1200      60.0  
   1680x1050      60.0  
   1400x1050      60.0  
   1280x1024      75.0     60.0  
   1440x900       59.9  
   1280x960       60.0  
   1152x864       75.0  
   1024x768       75.1     70.1     60.0  
   832x624        74.6  
   800x600        72.2     75.0     60.3     56.2  
   640x480        72.8     75.0     66.7     60.0  
   720x400        70.1  
DP2 disconnected (normal left inverted right x axis y axis)

Here's the problem:

  • starting from a cold boot, both external monitors work (e.g. I can place windows on them and see the windows)
  • if the screensaver kicks in and the monitors go to sleep (not just the black screensaver, but all the way into power-save), there's about a 50-50 chance that the left-hand monitor (HDMI1) will wake up and only show black.
  • the monitor is detected, and I can put windows there, move the mouse into the space that the monitor occupies, etc.

I know that the monitor is working and connected:

  • on-screen menus work, and it will recover if I reboot, so the monitor itself isn't broken
  • I have verified that the input selection on the monitor is correct (verified through on-screen menus); also, the monitor will auto-select the correct input, so it seems like the laptop is driving something onto the output
  • The monitor isn't powered off: the blue power-on indicator LED is lit, and I can see that's it's being driven black, there's just nothing being displayed.

Things I have tried:

  • pm-suspend, counting to 10, and then resuming will usually recover -- I will be able to see what's on the monitor. I'd generally prefer to not suspend, since this can cause problems with other things I have running.
  • xset dpms force off, waiting until the monitor goes into power-save, then a few seconds more, and then wiggling the mouse to reactivate will sometimes cause a recovery, but this is much less reliable than suspending.
  • xrandr --output HDMI1 --off, waiting for monitor to go into power-save, and then xrandr --output HDMI1 --auto; this didn't cause a recovery in two attempts
  • rebooting always recovers the monitor, but this is undesirable because I have to re-create my entire work session.

And, as I was writing this question, I tried the dpms force off trick and when I wiggled the mouse to reactivate, that second monitor flashed horizontal "rainbow" stripes. Turning off the power to the monitor and turning it back on didn't make the stripes go away, they seem to be driven by the laptop. Another round of dpms off gives me a gray screen.

This dmesg output (I believe this coincides with what is described in the previous paragraph) may be relevant:

[517791.806047] HDMI hot plug event: Codec=3 Pin=5 Presence_Detect=0 ELD_Valid=1
[517791.806118] HDMI status: Codec=3 Pin=5 Presence_Detect=0 ELD_Valid=0
[517791.885438] HDMI hot plug event: Codec=3 Pin=6 Presence_Detect=0 ELD_Valid=1
[517791.885487] HDMI status: Codec=3 Pin=6 Presence_Detect=0 ELD_Valid=0
[517792.100397] [drm:intel_disable_transcoder] *ERROR* failed to disable transcoder 2
[517803.480534] HDMI hot plug event: Codec=3 Pin=5 Presence_Detect=1 ELD_Valid=1
[517803.480598] HDMI status: Codec=3 Pin=5 Presence_Detect=1 ELD_Valid=1
[517803.484308] HDMI: detected monitor VX2453 Series at connection type HDMI
[517803.484316] HDMI: available speakers: FL/FR
[517803.484325] HDMI: supports coding type LPCM: channels = 2, rates = 32000 44100 48000 88200 96000 176400 192000, bits = 16 20 24
[517803.592203] HDMI hot plug event: Codec=3 Pin=6 Presence_Detect=1 ELD_Valid=1
[517803.592266] HDMI status: Codec=3 Pin=6 Presence_Detect=1 ELD_Valid=1
[517803.595931] HDMI: detected monitor VX2453 Series at connection type HDMI
[517803.595941] HDMI: available speakers: FL/FR
[517803.595951] HDMI: supports coding type LPCM: channels = 2, rates = 32000 44100 48000 88200 96000 176400 192000, bits = 16 20 24

How can I go about troubleshooting this?

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