The size and shape of the picture on your screen is set in two places- the Tv and the cable box. So you have to use both remotes to find a combination of size and shape that you like. On the RCA remote-
Left arrow/FORMAT Press repeatedly to change the screen format: Normal, Zoom, Center, Stretch. Go to page 39 http://support.ttetech.com/RCATV/Assets/PDFs/L40HD36_E001A_IB_e-08.pdf for more information on screen formats
On the Motorola DCX700 it's a little more complex. Basically you need to enter that secret menu again (Power off the cable box, Press MENU on the cable remote) and setup three things:
1. TV TYPE - set to 16:9
2. YPbPr/HDMI OUT - set to 1080i ONLY (un-select everything else)
3. 4:3 Over-ride - set to STRETCH (if you don't like black bars on the sides of non hd channels)
See the manual starting on page 29 http://www.nwtel.ca/media/documents/tv/dcx700_userguide.pdf
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