I have for sale an original Yamaha 128kB RAM board. It came from a working YIS503IIIR (which now has a 1MB board). The price is €45.
It will work in many Yamaha MSX machines provided they have RAM on a daughter board and the mapper circuit has been populated on the main board (this can be retrofitted if needed but I do not know all the details but I can get you in contact with someone who does).
If you are interested please send me an e-mail. The address is on my profile page.
