video interference?

lwaynej lwaynej at
Tue Feb 19 20:32:28 UTC 2008

On Mon, 2008-02-18 at 16:38 -0500, Bill Davidsen wrote:
> Frank Cox wrote:
> > On Mon, 18 Feb 2008 15:59:12 -0500
> > Bill Davidsen <davidsen at> wrote:
> >
> >   
> >> I'm guessing some device is injecting 60 cycle into your system 
> >> somewhere, and if you can avoid it you can avoid finding the device. I 
> >> don't think it's your monitor going bad, although I've never seen this 
> >> with an LCD display.
> >>     
> >
> > I moved my computers around again and "reclaimed" my previous desktop computer,
> > the one that I was using up until I got this one.  Now the problem appears to
> > be gone.  I'm pretty sure it's something flaky about the onboard video in the
> > new computer -- this monitor seems fine when it's hooked back up to the other
> > computer.
> >
> >   
> If the problem is caused by a "beat frequency" issue then the frequency 
> of the video would be part of the problem and another computer might not 
> show it. I was hoping that moving the monitor itself would change the 
> problem, indicating it was interference. And because at one point you 
> thought changing the cable fixed it, I was hoping that the offending 
> device was off at that time, and when back on started the problem 
> again.You said you moved the computer with respect to the monitor, did you
> >> just move the monitor around?
> >>     
> >
> > I actually moved the computer from under my desk to under a table that's
> > a few feet away and around a corner.  Which was handy when I moved my
> > "old computer" back in here because I just put it back where it sat
> > before.
> >
> >   
> OK, if the monitor was moved without changing the problem then that 
> makes the interference less likely. I usually just rotate the monitor 
> ninety degrees and see what that does. ;-)
> >>  Get a new 
> >> coffee maker lately? ;-)
> >>     
> >
> > I actually had about half of my apartment and office rewired about two weeks
> > ago.  I re-did the ceiling tile in the kitchen and it seemed to be the opportune
> > time to rationalize and update the wiring.  But that was two weeks ago and the
> > problem didn't show up until this Friday when I hooked up my new computer.
> >
> > More and more, it appears that the problem is in the new computer.  I shall see
> > what I can round up in the way of a video card tomorrow (today is a holiday
> > here so the computer store is closed) and then go from there.
> >
> > I'm thinking that I should try an ATI card due to their new "open source"
> > policy.  My experiences with Nvidia cards on Linux were several years ago and
> > were uniformly bad.  Things may have changed since then (maybe) but I still
> > have bad feelings about it.  I still like the onboard Intel stuff because it
> > just works right out-of-the-box on a Linux install -- no drivers to fiddle
> > with or anything.  But that may not be an option in this situation.
> >
> >   
> Did you try changing the frame rate with the "video=" boot option?
> > I did put F8 on a Dell laptop for someone a couple of months ago.  It had an
> > ATI-something-or-other video chipset and it just worked too, somewhat to my
> > surprise.

If this is a flat panel monitor then I would not suggest changing the refresh rate.

Did you change display drivers about the time that this started
happening? If the driver sets the pixel clock too high it can cause
pixels to display wrong. Also, if the wrong values are chosen for the
PLL that controls the pixel clock you can get noise as well.
> >
> > I suppose what I end up with will depend largely on what Garry has on the shelf
> > in his shop at the moment.  Does anyone have any recommendations?
> >
> >   
> I'm an ATI fan as well, for the most part they just work.
> -- 
> Bill Davidsen <davidsen at>
>   "Woe unto the statesman who makes war without a reason that will still
>   be valid when the war is over..." Otto von Bismark 

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