As this FamicomWorld article explains, Nintendo of America did not have enough cartridge boards for their initial Christmas season. To remedy this, they resorted to mass producing universal Famicom converter boards and simply used Japanese Famicom game boards.
As the article states, the easiest giveaway to finding Famicom converters is to find 5 screw cartridges that utilize flathead screws rather than the proprietary gamebit they introduced in later on in the NES’ life. So with luck, you get a 5 screw Famicom game, open it up, and lo and behold, you have a converter:
Here is how I find them. When I inspect the cartridge pins, I look at the cartridge upside down, making it look as if I am checking to see if the game is dirty or if the pins are in good shape. However, what I am actually looking for is the asymmetrical pin pattern as described in the FamicomWorld article:
X X X <= As we see here, the pins are to the right.
XXX XXX XXX
XXX XXX XXX
As I said, I look at cartridge upside down so this is a flipped version of the text diagram shown in the FamicomWorld article. Here’s a pic of what I mean taken from a Gyromite cartridge (all pics are click to enlarge):
This, of course, differs from later games where the pins are instead centered symmetrically:
X X X <= The pins here are centered.
XXX XXX XXX
XXX XXX XXX
Here is a Duck Hunt board housed in a 5 screw case:
Here is a comparison shot of two boards with the differences circled in blue:
I have found that this technique of looking for asymmetrical pins to be very successful. It has, however, failed me on one occasion. I was at a pawn shop where I was picking out converter carts to buy when I spotted the asymmetrical pattern on a 5 screw 10 Yard Fight cartridge and a Kid Icarus cartridge. I had the list of potential converter carts handy and saw that both were not on it. I figured, hey, new additions to the list. I was wrong.
With the 10 Yard Fight cartridge, what ended up happening was that the board inside was not even 10 Yard Fight, but rather, a Zelda 1 board with the battery taped on. The Kid Icarus board ended up being a board that looked oddly familiar. I removed the taped on battery and saw that the Zelda 1 board and the Kid Icarus board were essentially the same, only the Kid Icarus board did not have a battery soldered onto it. I then grabbed my gold Zelda 1 cart and looked at it, ignoring it initially since it only had three screws and top hinges. To my surprise, it didn’t have gamebit screws, just flatheads.
So here then, is a new addition to the story of Nintendo of America’s launch titles. In Japan, they had the Famicom Disk System. Almost all Famicom Disk System games were capable of storing save data directly onto the disk. When Nintendo of America decided to bring some of those Famicom Disk System games to America, they found that they could not just stick a disk through a converter. They had to alter the games’ save systems in one of three ways:
-Removing the save system entirely (as was the case with Castlevania)
-Implementing a long password system (Metroid and Kid Icarus anyone?)
-Adding a battery (yay Zelda)
As with the holiday launch issue, Nintendo of America mass produced universal boards for these Disk System ports and simply flashed the eprom chips with the different titles, adding a battery as necessary. These universal boards also had the asymmetrical pin pattern which now makes a whole lot more sense given a universalized board production process. Here is Kid Icarus (left) and Zelda (right) respectively:
So there we have it. The asymmetrical method will be successful in helping you find a Famicom Converter Cartridge unless it was a game that was ported from the Disk System or a board swap with a broken game (which also happened to have been a ported Disk System game).