The issue may not be with the cables, it may be ports on either the Nintendo 64, or on your media receiver unit. You may want to check the connections to make sure they are clean and don't have any dust or corrosion on them. If there is no problem with the connections, it is probably just something wrong with the video output circuitry in the Nintendo. In that case if you do have the technical knowledge you may be able to open the device up and attempt to replace any faulty components.