I bought six Japanese Mega CD games to play in my NA Sega CD model 2. I tested them all in fusion with the region free bios pack I got from a member here and three worked with any bios I threw at them and one will require me to have a region switch installed in my Genesis 1. Two of the games (Earnest Evans and Thunderstorm FX) would only boot up if I used either the Jpn mega cd 1 or 2 RF bios. All I need to know is if a real NA Genesis will let you run a Japanese RF bios from the Mega ED to a Sega CD. Thanks!
You can use any region bios on any region console. So you can put a JAP RF bios into a USA console just fine. My understanding is that the jap bios is the most compatible, as it has something (fonts?) the other regions do not.
You might run into problems if you use a non TRAY type BIOS on a TRAY console (duh can't eject lol). Also the Wondermega1 BIOS actually do work on non Wondermega hardware but Wondermega2 seem to have different chips in it and due to that it's BIOS won't work properly on anything but a X'EYE or Wondermega2 unit. CDX/Linguaphone seem to use similar chips to Wondermega2 but I don't have either and can't test such. As per regioning, using a JP MEGA-CD BIOS on a SEGA-CD of same type for example, doesn't affect anything but cosmetic look besides the fact that some Japanese titles go out of their way to make sure you're playing on a Japanese MEGA-CD unit (it does check memory regions for vestiges of EXPORT BIOS or EXPORT boot up logo) probably as defence against Datel's CDX device.
