Yes it could be the cable, but I think it would be a pretty rare
failure mode, maybe even a freak. I looked twice to make sure - this
IS a CRT monitor. In that case if the chassis has a floating filament
supply this could be an HK short in the green gun.

The trailing positive that makes the white after black green also
makes the black after white on some of the text magenta, which is
minus green. The frequency response of the green is limited, too much
capacitance. A standing wave anywhere in the green path could also be
at fault as someone already pointed out, but lots of CRTs short out
this way.

If so, if I have a print of the vid finals, the CRT soicket board, I
can maybe figure out how to EQ the vid output. I have done this more
that once. However I did that on NTSC units and I didn't worry about
FCC part 15 or anything. Those things only have about five Mhz video
bandwidth, this might be different.

There is a way to do this on almost any CRT based monitor, but the
question is whether it is worth it or not. The focus isn't really all
that bad but it ain't that good either. You have to differentiate that
from the smear in the green though, if the green was sharper it would
look sharper overall.

Without the print of the CRT socket board, ar at least a sheet on the
IC(s) on it, it's about impossible to do anything. In fact that's true
even if it's not an HK short.

J