Comcast is moving channels from analog to digital so non-local channels (usually above 30) will disappear unless you have a box. See this. You may need to rescan if local channels are missing but they should be accessible without a box. If you're using a box, try resetting it. If you're missing channels that you should have access to even with a box call 800 Comcast. They may need to send a signal to the box or have a tech come out and replace it.
I have a new Samsung LGTV, just got it about two months ago, so I shouldn't have any problems with dropped channels. Once they started converting channels over during the summer with my old tv I did need a box. It's only seems to be those two channels that have issues, know what it looks like on an analog and this isn't it. And why only two channels when all the other channels look good?
If the signal is scrambled when directly connected you'll need a DTA (digital to analog) or a regular STB. I believe comcast is providing them for free for the 1st year. If the signal is still scambled thru the box and you should have access to it then you'll need to call Comcast. If your getting a signal but the picture is not clear or the channel states "channel should be available" msg then you may have a weak signal that is affecting only certain channels. On the moto boxes you can check your signal strength by following these steps but you may need to call and have a tech check the lines.
Now if I switch to a HRC (harmonic related carrier) option or an IRC (incremental related carrier) rather than sticking with the STD, would that work? I don't have an analog tv anymore, so I don't find the reason of getting the scrambled channel.
Just tried the HRC, nope nada, ziltch. On the IRC scanning now. Emailed Comcast to see what they say. Just don't know why I can't get certain channels on a non analog tv with a digital broadband comcast box. Maybe its just me.