I am trying to help my parents hook up their tv setup in their motorhome. They just purchased a 20" Vizio lcd. The have DirecTV hooked up using the svideo input and rca cables for the audio. They also have a switcher box using coax that has their dvd player, cable tv, and antenna hooked up. Here is the problem. The DirecTV plays fine through the svideo input. All of the others using the coax hooked to the tuner coax input does not work. What are we doing wrong?