Re: Debian 7.8 amd64 xfce lightdm login screen second monitor sleeps but does not wake up

[Henrique de Moraes Holschuh <hmh@debian.org>]

On Mon, Apr 27, 2015, at 14:57, David Christensen wrote:
>    Intel Core i7-2600S processor with Intel HD Graphics 2000
>    DVI analog port
>     Intel DVI to VGA adapter (came with motherboard)
>    DP port
>     StarTect DP2VGA2 DP to VGA adapter
>     ViewSonic VX2260WM LCD monitor
>   Debian 7.8 amd64 (Wheezy) with Xfce desktop environment
> 
> If the machine is at the lightdm login screen and left unused, after ~10 
> minutes, both monitors go dark (I'm calling it "sleep"; I don't know 
> what Debian/lightdm/Xfce/X/power manager/whatever calls it).
> 
> If I then press the Shift key, the LG monitor "wakes up" (or whatever 
> it's called) every time, but the ViewSonic monitor sometimes does not 
> wake up.

This is likely either a hardware, firmware (yes, really), or kernel issue.

First, check if you're using the latest BIOS/UEFI for your motherboard. If you're not, chances are an update might fix some issues.

The second detail is that DP to VGA is an active adapter, and such adapters can cause issues, including and not limited to not working properly as far as VESA DPMS signaling over VGA is concerned (this is what signals the monitor to go into standby or sleep modes, and of course, to go out of those modes).

> I don't know how to figure out what software package and/or 
> configuration file(s) control the monitors when lightdm is at the login 
> screen.

> Any suggestions?

Try an Debian8/jessie live-cd.  If that fixes it, you know you will at least need a newer kernel, and you might want to consider updating to Debian 8.

But I'd try the system firmware (BIOS/UEFI) update first, if one is available.

Also, DP to DVI is usually a much safer conversion than DP to VGA, especially if the DP port is "dual mode", which allows for a passive converter (it can output DVI-compatible signals directly).

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique de Moraes Holschuh <hmh@debian.org>