Hmm, bad news is: I figured out one of the big frame transistors on the WG6100 in my Tempest machine is bad. Good news is: I know how to replace that part.
Hopefully that fixes the monitor, though I'm going to poke at some other components to see if there's not a further underlying cause. Nice thing is that I've fixed this monitor before by replacing half the parts, so I'm mildly optimistic I can do that again worst case.