Here are some photos of the ROM switcher board in my Kawai R-100 Drum machine. The expansion board is dated 1987. My unit contains three 4Mbit mask ROMs:
MN234000KAA, MN234000KAB, MN234000KAC
I think these ROMs are the original R100 and R50 and the R50e judging by what I’ve read elsewhere on the web. The sound format is 12-bit (non-linear) with a 32kHz sample rate.