Hello all.. I have a monitor that allows viewing of the retrace and
overscan periods, so I somewhat fond of it. However, it consistently
displays this symptom:

I've been going by the canonical repair faq.. and reading through it
for the umpteenth time I discovered a mention of "vertical foldover."
I hadn't seen that before. Is this what's going on in that photo?

Also thank you F.Z., I probably can't screw it up with advice that
clear.