Macintosh II: Cure For Vertical Green Lines at Bottom of Screen
I have a problem that occurs on a Macintosh II with a color monitor and a
video expansion card: Vertical green lines appear on the lower third of
the screen when you select the 256-bit mode from the control panel.
However, when in the 16-bit mode, the monitor behaves normally.
The problem may be a video RAM problem. Try replacing the eight extended
video RAM chips with known, good video RAM. If the problem persists, you
may need to replace a defective video card.