Assembly 904-5874-8.2.  Schematic 081-8240.  Stamped 421-2925B on the back of the board.  Battery will probably need to be replaced.  Zilog Z180 microprocessor.  Purchased new in 1999 by an Allen organ service center that is now out of business.  Never used, kept in a service kit.  Sold as-is.  Cost includes shipping in the continental US only.