Emax

Hi,

I have an Emax II Keyboard with 2 MB and an Emax II rack with 8 MB. Both work fine. I tried to swap mainboards but the keyboard doesn't boot with the rack MB. The upper line of the display shows black squares and all the buttons lights turn on. If i swap them again both Emaxes keep working. I noticed that the keyboard MB has an RN6 chip that the rack one doesn't have (the socket is empty on the rack MB). Any ideas of what that chip does ? Anyone knows which is the chip that store the sound memory size ? 

Thanks,

Diego