Comcast Set-up of DCT3412

I picked up my HD STB (DCT3412) at the Comcast office, set it up on my Samsung DLP set with a HDMI connection. I get all the non-HD content but no HD channels (and on the cable guide the HD channels aren't listed, or available if I put the number directly in). I called to get it updated, and COmcast must have sent the codes 100 times but it still doesn't change. They are sending out a tech Friday, but I was wondering if anyone could come up with an easy change to teh box set-up I could do without the visit. I can't believe it is signal strength related, has to be some setting on teh box or comcast is sending teh wrong codes to the box to allow HD content through. Thx