I would start at the TV following the coaxial cable back to the amp switch. Sounds like a connection is loose or not connected. This is often a tedious task but it should yield positive results. And, don't rule out a bad cable, the use of a jumper coaxial is handy. Attached dia. it the amp switch, normally located below the TV. All on mine were loose. It happens....
Don & Dona W/yorkies Gizmo, Master Chief, & Tali
2011 Flagstaff 8528 BHSS 2015 Ford 6.7 XLT
2010 Full Timers & Still Going