I did set up dual monitors few times on few of my boxes, with 3 video cards :

Radeon 9250 AGP (have 2 of them) - with open source ATI driver
Geforce 6200 PCIE - with nouveau driver

In all cases I connect 2 LCDs. one 1440x900 or 1680x1050 to DVI and one 1280x1024 to VGA (all the cards have DVI and VGA out). The LCDs are the same ones tested with all cards :

1440x900 : Benq FP-92W
1680x1050 : Teac T2005L15 (identified as KTC2002 in xorg)
1280x1024 : Proview PQ-721KP

Tried on different boxes runnning Arch linux, different kernel / x / drivers / kde versions



Problem is - in all those setups, one monitor allways randomly blanks for a split second and comes back (incl. switching of the backlight, and displaying the "Source : VGA" or "Source : DVI" title as if it was switched off and on)

This happens randomly, but (more pronounced with the ATI cards) related to me clicking on stuff or the display changing (even if the changes are on the second screen)

With the Radeons only the monitor connected to DVI blanks. And the 2 radeons do it in different frequency, one is more often and one less

With the Geforce only the monitor connected to VGA blanks

When I test with 1 monitor (other one disabled in xorg) : Radeons sometimes still do that to DVI monitor but rare (much less than with VGA connected) (VGA monitor never blanks). Geforce does not do it at all and has problem only when 2 monitors are connected



I first thought its a hardware issue (the cards are from junk), but it happens the same with totally different hardware (exceps using same monitors) so i no longer think it is

There is nothing interesting in Xorg.0.log

Not sure if relevant, but my old Nvidia 7950GT always did this in Windows 7 whenever I switched on my USB wireless XBOX controller...

E. g. all's fine, then, when you press the X button on the controller to switch it on, instant screen blank for about a second and then it comes back all fine and you can go on working.

Sure I know this sounds totally irrelevant, but it seems that this happened in Windows due to some hardware setup or loading issue, and it ALWAYS happens. Press X on controller, screen blanks and then comes back up.

My point being I think this is what is going on there too. It might be power-management (DPMS) related? E. g. the screen power-cycling in certain situations?

Have you tried switching off DPMS in your xorg.conf for the X-server? E. g. taking out any lines that have DPMS in them in your xorg.conf:

E. g. I'd remove 'Option "DPMS"' above, and see if that changes anything.

Also, this might be some kind of probing the x-server is doing, I've seen my screen switch off completely (as if DPMS-blanked) and then come back up during installs of display drivers and other hardware drivers (ok, under Windows too, but I think the principle remains the same.)

I'll try removing DPMS



What is different here is :

It happens on 3 completely different systems (and with somewhat different versions of components of the OS since installed at different times)

The monitors are the same, but they work ok when alone, and there is no specific monitor to blame (problem can happen with monitors 1, 2, 1+2, 1+3, 2+3 - no monitor looks like causing problem by itself)

It does not look like sensitivity to power fluctations - it is very related to when i click stuff on the computer, or change the display content (view empty desktop - get few interruptions. view animated GIF - get a lot. click stuff - get sometimes). Power supplies in all computers and monitors are intact without failing capacitors etc

The interruptions happen all the time (randomly and not always, but tend to be related to clicking stuff etc), not only once on power up

Thanks