I actually send my MegaCD tray Jap eprom to a friend.
He asked me to send him the original MegaCD bios to fix my bad eprom.
I found the fullset rom of genesis including the archive Sega-CD BIOS.7z
Inside of it there is the file called:
Mega-CD Model 1 BIOS V1.00 (J) [!].gen
I don't know if it is the file to burn on eprom to fix it because it's a .gen file.
Do you know if it is the correct file?