I had the same issue in our TT when it was new. What I found was the cables from the outside hook up and the antenna were reversed at the amplifier box. I have the Winegard Sensor series antenna/amplifier and the antenna is actually powered from the amplifier box over the cable. To check get a short cable and a tester, turn the amplifier on and plug the short piece of cable into your outside hookup. If you have power (DC) to the outside cable hookup it is reversed, at least in my case. I found that power on or power off made no difference in receiving a cable signal, so my amplifier must block a cable signal on the Antenna port. Remove the Amplifier from the wall and reverse the inputs. Everything works now and I even get better over the air reception with the power actually getting to the amplified antenna.
