One LCD is flickering on a dual monitors setup

I just added a second LCD and now my primary LCD is flickering once in a while (tiny thin white lines running up and down, it's not very obvious or very distracting....but it was never like this with just one LCD monitor or before adding my new/2nd LCD monitor.

Could it be the ATI display driver? I've ATI HD2600 Pro with dual DVIs and I'm not a gamer, so everything is at defaults. I was told that HD2600 Pro with dual DVIs is more than sufficient for non gamer to support dual LCDs, is this right? or my video card in under power?

I must had uninstall/reinstall the video card driver (8.5/8.11/8.12) at least 7 or 8 times, cause XP kept thinking my new LCD (Samsung T220) was the primary monitor and my original LCD (samsung 226BW) was the secondary monitor. I have the MS WinColor to manage different colour profile (.icm) for both monitors, but somehow whenever I selected an icm for Samsung 226BW, the colors changes in the Samsung T220...what a mess.

Any help/feedback will be much appreciated.

Primary monitor Samsung 226BW (native 1680X1050) currently running at 1280X800
Secondary monitor Samsung T220 (native 1680X1050) currently running at 1440X900

I am not sure if this is your problem, but are both monitors running at the same Hertz?

I must had uninstall/reinstall the video card driver (8.5/8.11/8.12) at least 7 or 8 times, cause XP

For future reference, in XP, you can select which monitor is the primary...

-Right click on background
-Select properties
-go to Settings tab
-Select monitor in window
-check "Use this device as the primary monitor"

Also, for a multiple monitor system I would recommend ultramon. It is a helpful utility program.

Probably nothing to do with your flickering, but my 1680 X 1050 (Native) monitor looks terrible at anything other than native resolution. My OS keeps switching it to 1280 or 1400 at random and the text is almost illegible till I change it back. I assume you know this and you chosen those non-native resolutions for a reason.

And turk690's explanation seems reasonable. Easy enough to test by temporarily separating the monitors. I've only ran dual monitors a few times, but they were different brands.

Originally Posted by turk690

I had a similar problem (occasional flickering white lines, in fact unobstrusive on one of the monitors) when I put two Acer LCDs side by side. First they were both connected to the same graphics card (one DVI, the other D-sub). No amount of tweaking with the graphics card (nVidia 9500GT0) driver settings changed the situation. Then I connected one monitor to another graphics card in another PC to test for something. With the monitors still side by side touching one another I was shocked to see that the oh so subtle flickering lines were still there! Then I found this: if I turned off the monitor with the good picture (completely removing the AC plug) the flickering on the other went away. Or, as in my original set-up (one graphics card with a primary and secondary monitor), if I separated them at least 5" apart the flickering on the one that had went away. With the physical gap between them the initial purpose of having both side by side for an extended work area is now kvetchy.
This is what my research brought up: even on two identical monitors, the frequency of their switching power supplies units (PSU) or fluorescent lamp inverters are rarely exactly the same. Even if they are, the phases at the exact moment might be different. If they are not heavily or precisely shielded and enclosed (as is often the case), they leak RF out. This is not a problem if a monitor is alone, or another nearby poorly shielded switching PSU from some component has a radically different switching frequency (not a multiple or harmonic of the first PSU). But if the frequency or phase are nearly the same then the difference may reflected as the flicker that is noted on one or both monitors.

Thanks you so much turk690, no more flickering on my monitor

I really appreciate you taking the time to write and the very logical explanation. Those who bring sunshine into the lives of others cannot keep it from themselves.

Yes redwudz, I don't keep my monitors at their native 1680X1050 cause the text is way too small......I'm lucky cause all three of my LCDs, one LG (S-IPS panel) and two Samsung all display perfectly even not at their native resolutions after some calibrations and using some very good .icm created by some of the LCD "guru", lol.

Best regards.