I've been having an odd problem for the last couple of weeks. I have a TiVo Series3, in Watertown, with CableCards. A couple of weeks ago I lost these channels: 802/808/814/915. It's not a CableCard issue since the TiVo reports lack of signal -- when it's a CC failure it's just a blank screen. I had a tech come over and he put a meter on the wire and said it all looked normal (and thus not Comcast's problem -- at least he didn't charge me for it). Then I had the idea to attach my cable to my TV and have it do a digital scan. Interestingly, of the over-the-air channels on the cable, it failed to tune exactly the set of channels that are missing on the TiVo: 2.1(802), 56.1 (808) and 38.1 (814). I should mention that the SD versions of these channels work fine.
So I was sure that something was wrong coming out of the wall, but here's the thing: I went down to the Comcast office and picked up one of their DVR boxes and plugged it into the wall, and that box DOES get the missing channels. So the only thing I can think of, with my limited knowledge, is that Comcast has started using SDV and I'm going to need whatever their switching box is that they're supposed to supply. On the other hand, I don't know if the symptom of SDV is missing video, or the wrong channel or something.
Anyway...anybody else seeing anything like this?