We have a Tivo Series 3 HD that was working like a champ for ~4 years. Recently it started having what I'm calling a tuner failure, but I can't determine if the problem is with the CableCard(s) or the Tivo. I've called Comcast and Tivo for support, but they can't seem to figure it out either. Problems: Started sporadically, when we'd go to live TV, no signal or wrong signal would be going to the TV. TV (Samsung) would show black screen with message of "unsupported mode" in a floating box. To determine if this was a Tivo or CableCard issue we went to the local Comcast office and exchanged the CableCard. Put in the new M-CableCard and went through the setup and activation ... now the Tivo shows a message something like cannot access this channel, but it is a Tivo message, not a Samsung message like before. Third time we try two S-CableCards, go through setup and activation and everything works great for about a day, then we get the same Samsung message again, unsupported mode on both live TV tuners. Forth CableCard (could be one of the previous ones, Comcast doesn't seem to know what they are doing), go through setup and activation, nothing works for about a day, then one and only one tuner starts working (I think we re-ran the Tivo setup). Meaning that if you press live TV once there is TV, press it again ... unsupported mode (Samsung message). This whole time playing previously recorded shows still works fine. Also strangely, going to the KidsZone/Guru Guide selection on the Tivo menu brings up this unsupported mode Samsung message. I didn't confirm this happened in all instances, but at least with the first and second M-CableCards it occurred. Has anyone had any experience with this? Is my Tivo dying? or is the problem with the CableCard or the way that Comcast is activating it? Any suggestions for how to troubleshoot where the problem lies? I don't want to replace the Tivo if it's a CableCard activation issue, but I don't know how to tell which is the problem. If it is a Tivo issue, is this something Weaknees can fix? Help Please!