Now, that's not to say it wasn't displaying an image; it was displaying it just fine, except about twice as bright as it ought display it, which is no good. In fact, I could quite easily see the retrace lines, which you most definitely shouldn't be able to see under normal operation.
Being the handy guy I am, I went and ate dinner. After I was done my dinner, I cracked open the monitor and re-adjusted the primary brightness setting on the flyback transformer, all while managing to resist the temptation to lick the big red wire (it's important to not lick the big red wire when working inside a monitor).
Of course, what I neglected to do was to check and adjust the focus while I was in there, as the brightness change drew it slightly out of focus. Perhaps if I'm feeling impish some other day I'll crack it open again and give it a tweak. It's not all that bad, really.
I'm just glad I don't have to buy a new monitor right now. All 3 of my current crop of monitors are on their last legs, but they'll hopefully hold together until next summer.