I have a 2014 Winnebago Sightseer. In the compartment above the driver side is the connections for satellite hookup. I have a DISH Wally receiver in which the HCMI cable goes into the wall and then c...
We have a Itasca Sunova 33C. Almost the same as your Sightseer. On our there is a HDMI splitter in the cabinet behind a removable panel on the floor under the retractable TV. Maybe it is bad or the short HDMI cable between it and the TV. Good luck.
BTW, yes HDMI cables can break which is why I use a short extremely flexible HDMI cable between the installed cable and our receiver due to the sharp turn it has to make.