YUCK!!!!!!!!!!!! That is kinda nasty! :O

The two Radius Logos displayed at startup make me think the vertical sync timing may be way off and you're getting the equivalent of an intermittent, sorta stable digital version of screen roll on an analog TV. A bad vertical sync rate crystal can, or ALL the crystal cans ought to be fairly easily replaced as a first step. See what the electron pushers around here think of that WAG.

Such might also explain some of the other artifacts as well . . .

. . . or not. :-/

edit: looked more closely, I only see the one crystal can. Whatcha' think gang?