Hi there,
Been a while since I've been around. But I'll chime in here -- I had a very similar problem. The video coming from my 990 was flaky. I never switched through it, so the only reason I had it hooked up to the TV was for the OSD. I did component and S-video. I also used those same connections to another TV. It would come and go and "roll" on the screen like old-timey bad reception. Sometimes it would not work at all. I tried different cables. Always the same result.
Finally, Steve sent me another 990, and I never had another problem with the OSD at all. So I can tell you first hand that this kind of thing is possible. Hey, all types of problems and failures are *possible* with a machine like this.
Of course, now I have the intermittent background noise in "upsample" mode, but that's another story.