Just bought an RGB-cable for my Sega Megadrive 1, but there is a weird problem with it. When it's connected, all I see is thick coloured lines going from the top to the bottom of the screen, wich seem to contain fragments of the "real" picture. Nothing more than that, and no chance I can see what's going on in the game! The sound does work perfectly though. Somebody have any idea what could be wrong?