RF only or have you tried AV hookup? Are you using Japanese TV or a different TV? You do understand that Japanese RF out does not work properly on USA NTSC TVs? You would need to use a TV that has built in basic cable decoder and switch to something like channel 93 or around that? I don't know what setting to use on other TVs around the world but not all can handle Japanese RF signal.
You can test by getting the correct pins on the EXT port for composite. If it shows fuzzy, recap is probably needed. If it shows good video, the RF modulator is probably failing.