Thanks for all the interest. Yes, modulator is built into the switching box and I've tried TV (which is what I kinda recall using when it last worked, if I watched more often than once a month or so I might be more certain of settings). Anyway, tried several - TV, AV, DVD changing input source as appropriate.
Jenson has all above inputs plus 2 HDMI. Why in this day and age Winnebago set it up for modulator is beyond me but was OK with til it didn't work
All cabling in the wall or behind the Entertainment panel where player and switching box are. Looking like I'll have to open it up and see what's connected to what.