Need help! Replacing Coregrafx RF unit

[Maker]

I did bought PC Engine CoreGrafx and with some reason that systems AV output has been repalced with a RF unit. Well, it works, but the image quality is kinda poor...

Of course I could try to make a RGB mod, but it just would be too hard for me to build the RGB-cable and I can't find any place where to buy one. So I did replaced that RF unit with a 5 pin DIN connector and I did watch here where to solder the pins correctly.

Then I plugged it to my TV with a AV-cable, but it just doesn't work. All I got is just black and white screen, no sound and picture wawes a lot.