I have a Winegard YA-1713 VHF antenna and a CM 4228 UHF antenna connected to a CM 7777 preamp. Recently I've lost all the channels on the VHF side (3) so I went to the roof and checked everything out but I didnt find anything obviously wrong. Both antennas are pointed in the right direction and no breaks on baulm that I could see from below. Sometimes the one nearby VHF will appear but only briefly. Channels on the UHF side are fine. I'm fearing my preamp might be failing...again.