[ltp] 1600 gray vertical bars on external monitor at 1600x1200

[Richard Neill]

Ben Pearre wrote:
> Hi!
> 
> R40 (2897gwu), latest Debian unstable, ATI Radeon Mobility 7500 (Xorg
> radeon driver)... more details below.
> 
> I'm trying to use an external monitor--a Dell 2000FP.
> 
> At 1280x1024 and lower, everything is great.
> 
> At 1600x1200 (native resolution of my external monitor, being driven,
> in this case, by the Thinkpad D-sub analog out), I get a weird pattern
> of gray vertical bars (1600 of them, I suspect, although I have not
> counted) over the whole monitor.  It's most visible on a solid
> background (especially white or black), but it's omnipresent.
> 
> Even weirder, the monitor's built-in zoom function magnifies these
> lines.  xmag, however, does not.  So the signal is probably coming
> from the DAC.  However, I really hope against reason that I'm missing
> something and there's a software fix.

Sounds like a frequency problem to me. What happens if you change the 
HorizSync and VertRefresh values in xorg.conf.
2 possibilities

  * The range is too large. Force it to exactly 60Hz.

  * The range is too small - sometimes, you need some rather unusual modes.

/var/log/xorg0.log will help.


Eg:

Section "Monitor"
     Identifier "monitor1"
     VendorName "Generic"

     #Force VertRefresh to exactly 60
     HorizSync 31.5-90
     VertRefresh 60


     #Or, allow a much larger range.
     HorizSync 20-140
     VertRefresh 50-275



Some flat panels are excessively fussy about what they are driven with. 
Fortunately, you can't hurt them with the wrong range (unlike 1990's era 
  CRTs).


HTH,

Richard



P.S. Also try xvidtune.