its possible that the rf cable is bad. I have a apf tv fun 406 that has the same problem as your game. I took the top off the rf box and took a multimeter to it, i found it was my cable thats bad.
place a lead on both ends of the cable, and set your multimeter to 20 ohms. if its good, it should have a constant reading.
if the numbers cycle randomly (on a digital) then, the resistance is too high and you will need a new cable