|You didn't have to be all that
smart to be a service technician at a World of Nintendo
booth in a mall. The NES, like most video game systems,
are designed to be easy to repair, and diagnostic test
cartridges like these were designed to test every part of
the console, so a malfunctioning chip or part can be
identified and replaced quickly.
This cart, differing itself from all others by its hot yellowness and its depiction of Mario hefting an NES cart as big as he is, goes through a series of tests and after finishing them puts you in a screen that shows what joypad buttons are being pressed as you press them. All in all it's not incredibly interesting, but I can see how these diagnostic carts would be rarer than your average NES game. The average World Class Service shop had at least one or two of these carts on hand, so they lie in rarity somewhere between an extremely rare NES game and a prototype cart.
Thx: Alan Davis