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really part 2 of this question, but its a different issue than what i thought. I've been doing some testing, the screen seems to be non flickery if more than 1/4 of the screen is black, if i have any other colour taking up more than 3/4 of the screen there's flickering along the horizontal axis (only).

I've ruled out it being flickering due to frequency (i had that before), so.. what could the issue be?

Its an old CRT (a compal F708) if it matters, OS is windows 7 (i haven't been able to test it in anything else yet), running at 1024x768 at 80 hz

EDIT: further testing shows its worse when there's lots of red or green in the screen. blue is not as bad. flickering stops totally when i reduce the size of the non-black area. I've not tried other combinations of colours.

By flickering, a horizontal line looks flat, and a vertical one looks wavey

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  • And if you turn the brightness down?
    – Ignacio Vazquez-Abrams
    Commented May 18, 2011 at 1:49
  • ... post that as an answer. that worked. But how?
    – Journeyman Geek ♦
    Commented May 18, 2011 at 1:55

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The three beams that a CRT uses to project the image onto the phosphors have an electromagnetic charge (because, well, they're electron beams), and the charge on each beam affects the other two beams. The effect can be anything from a slight enlargement of the image to a disruption in the form of flickering. Reducing the brightness of the image reduces the strength of each beam, in turn reducing the disruption.

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Have you tried degaussing the monitor?

I had an old monitor that would get that way. It likely is just the fact that it's aging. Magnets control the direction of the electron stream in CRT, and when there is a buildup of static charge, it affects the EM field lines, which can cause this, which degaussing can fix. However, if they are just aging and deteriorating, there may not be much you can do.

When you have so much white on your screen, there are a lot of electron streams being fired (for each pixel). Because they each have an EM field, they can interact with each other. That's why you would see picture warping in very bright images on CRT displays (including TVs), than images that are full of black areas.

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  • first thing i tried, actually.
    – Journeyman Geek ♦
    Commented May 18, 2011 at 1:54
  • or any other colour. It makes sense, but i think ignacio gave me the actual solution ;p
    – Journeyman Geek ♦
    Commented May 18, 2011 at 1:58

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