On Super Nintendo games, there are two notches cut out on the backside of every game. They fit around two pegs that are inside the slot where you insert the cart into your system. Super Famicom carts do not have these holes on them, and this is the only thing keeping you from playing Japanese games. Modifying your Super Nintendo is actually quite simple and very cheap (or free if you already have everything). You can still play your US carts just fine, so there is no downside to this. There are a few ways to play Japanese games, but this instructable will guide you through modifying the actual console itself by removing those two pegs.
Note : Whenever you work with anything, there's a chance you may break it. Be careful.
Step 1: Tools Needed
Flat, clean work surface
4.5mm Security Bit + Screwdriver handle
Small Philips Screwdriver
Xacto Knife with sharp blade
Small metal file or low grade sandpaper
Small lid or container (to put screws into)
Push pin or Needle
Q-Tips and Water
The only thing you probably do not already have access to is the Nintendo Security Bit for their special screws. You can easily find it on EBay (paired with it's 3.8mm counterpart for opening up the carts) between $5-10. If you need it, click HERE and order yourself up some.
I've read and tried some other methods for removing the security screws but I couldn't get them to work myself. Do a quick google search for alternate methods if you don't feel like paying for the bit.
Step 2: Open the SNES
Flip the Super Nintendo over so that the bottom is facing up. There are six security screws (2 near the surface, and 4 deep down). Grab your 4.5mm security bit, put it in your screwdriver handle, and crack that baby open. Since this is probably the first time you've opened it, the screws will be pretty secure. Make sure you put enough pressure down on it, and that your SNES is stable.
Remember : lefty-loosey, righty-tighty!
Once all 6 screws have been removed and set aside, flip the SNES back over, and then carefully lift the top half off.
Step 3: Remove Internal Screws
Now, lift out the internal plastic tray and you have disassembled the SNES enough to easily access the pegs!
If you want to clean your SNES, now is a great time. Depending on the situation, your SNES may be in need of it (I've seen things spilled into the slot). Take the canned air and spray underneath any of the internal components as well as any exposed parts of the circuit board to remove any big pieces of dust that may have collected. Use the water and Q-Tip to clean off any dirty surfaces, and wipe out all the creases and corners.
Step 4: Score, Wiggle and File
Once the pegs have both been broken off, you may decide that the break was nice and close enough that you can just reassemble it, but chances are it won't be. Filing or sanding down the excess will take the most time, and expect to spend at least an hour on it. Take the small file or coarse sandpaper (wrapped around a pencil or a stick) and just start working on it, making sure not to accidentally file a part of the plastic you don't want to. Slow and steady is key.
Step 5: Reassemble and Play!
• Put the plastic tray back on the underside of the top (make sure the faceplate is also attached on the top with the spring-loaded shield properly in place)
• Screw in the 7 philips screws
• Reattach the spring for the reset button
• Place the top back on the bottom
• Flip the system over
• Screw in the six security screws
Voila! Your system is now able to play Super Famicom games, so plug your SNES in and play!
Note : Super Famicom game carts are slightly smaller, so make sure you're inserting it correctly when you slide it in. The Super Famicom cart I had access to leaned forward a little, so I placed a thin piece of cardboard to hold it in place, and that did the trick to make the pins line up properly.