Couldn't find the scope probe, so I did some quick testing with my DMM instead, measuring a few of the outputs of the Y buffer boards. With the set tuned to snow, the readings were about 91 VAC all the way down. With a black screen (A/V input), about 116 VAC. Unless there's something special that I need a scope to see, it appears that the outputs from the buffer boards are good - if not, I would expect some kind of difference between the outputs to the live and dead areas of the screen, even if just measuring AC voltage. At this point would I be wrong to assume the panel is bad?