there are 4 channels from mexico which i received fine for the longest but during world cup playoffs i lost them. black screen. 80% quality displayed on rcvr. checked transponder info, symbol rate, VPID, APID etc. Now i only get video but no audio on Azteca 7, Nothing on Azteca 13-black screen, Azteca 40 comes in just fine. All three are on the same transponder. All out of ideas.