NES-21G-CPU-72P

Cartridge Board (huge pic to show details)

What Is It?

A very weird test board by Nintendo.
32K of PRG ROM
8K of CHR RAM
Spots for various chips

The Tech:

In this incarnation, it doesn't have anything on it but a ROM and RAM... However, there are spots on the board for a whole mess of other chips. These chips all connect to the expansion connector pins. Obviously they had SOMETHING in mind for the exp. conn. Whatever it was, this could've tested it.