Thank you for te info. May I have to change the 7800.rom.
no, you simply have to find the option to switch between common a7800 and the prototype BIOS
alternatively, you can run by command line
mess.exe a7800 -bios 1
Wow great. Thank you so much ! It´s really simple and working.
What's interesting about this is that the "PAL" 7800 BIOS with the built in Asteroids game is actually both NTSC and PAL. ;-) Though it was only previously enabled for PAL. The two new 7800 BIOS prototype's that were found are NTSC only though.