My problem has been fixed, but it wasn't as easy as you'd think.
First of all, you can follow the discussion of this on comcast's forum too if you want: http://forums.comcast.com/t5/Channel...ls/m-p/1070271
I emailed WHTM (abc27) and WGAL (nbc8). WHTM got back to me immediately. WGAL apparently contacted comcast. Comcast called me (the message they left was quite humorous to me) saying they spoke to WGAL and were sending me a service tech guy for free to remove a TRAP.
WHTM's guy explained this to me: "Ask them (comcast) specifically to come out and remove the trap on your cable that is preventing you from getting 27 and 8. This trap was placed on customers that had limited-basic serviceand now Comcast appears to have moved local channels into that trapped frequency range."So, that's what each of you who have Limited-Basic comcast service in the Harrisburg Area need to do. I suggest asking to speak to a supervisor when you call. Or you can try emailing comcast at http://www.comcastsupport.com/com/email.asp
After the tech guy removed the "trap", my wife did a rescan on the TV, and voila, 8.1 and 27.1 are back... along with 47 music channels (that's more than what used to come thru clear-QAM). I'll list what the channels should be in my next post.
Good luck everyone! Feel free to tell comcast that you know of two people who had this done for them for free (me and another user from the comcast forums). After all, this whole issue came up because of comcast moving 8.1 and 27.1 to different frequencies than what they used to be on. Tell them that Bob Good from WGAL and Keith Blaisdell from WHTM are aware of this situation. (a big thank you to both of them!)