NES Controllers to Famicom Adapter compatibility

[samson7point1]

Made a two controller adapter for using NES controllers on the Famicom using the diagram from this post:
https://www.famicomworld.com/forum/index.php?msg=55602



For materials I used NES and NEO GEO extension cables.

The adapter sort of works, but I'm getting really weird behavior from it. Just wanted to see if anyone out there had more experience with this and could tell me if what I'm seeing is "normal".

I have a first generation Everdrive N8 and both control pads work just fine navigating the menus.
If I launch Super Mario USA from the Everdrive it doesn't detect any buttons from the controllers attached to the adapter (the hardwired controllers still work fine).
If I use a genuine Super Mario USA cartridge it behaves the same - no response to the buttons on the adapter.
If I launch Akumajou Densetsu from the Everdrive, no button presses are detected.
If I use a genuine Akumajou Densetsu cartridge the controllers attached to the adapter work perfectly.
If I launch the NES test cartridge from the Everdrive, no button presses are detected from the NES controllers.
If I launch Contra from the Everdrive, both P1 and P2 controllers have full functionality through the adapter.
If I launch Duck Hunt and connect a Zapper to the P2 socket on the adapter, the Zapper doesn't work at all - no gunshot sound when pulling the trigger. The P1 controller attached to the adapter seems to work normally (select and start work)

So far I've done this to troubleshoot:
- Quadruple checked the wiring by buzzing out every connection
- Checked the whole adapter for shorts
- Checked 133MHz's diagram against other pin diagrams to confirm the function
- Checked resistance on each line (nothing over 1 ohm)
- Replaced all the electrolytic capacitors on the Famicom
- Replaced the 7805 power regulator on the Famicom
- Replaced the power supply with a Triad 9v/1.3A C-
- Tried the adapter on a different Famicom
- Tried the adapter with a different Zapper
- Tried the adapter with different NES controllers
- Verified the controllers and zappers work with an NTSC NES

Am I missing a step? Does one of the pins need to be grounded out to switch modes or something like that? Is this just how external controllers work on the Famicom?

[jd213]

Super Mario USA doesn't poll controller inputs from the extension port. Same for a few other Famicom games like Robot Gyro, a lot of games developed for the NES, and probably a good bit of hacks and homebrew.

You'd need to splice NES extension cords onto the internal FC controller inputs in order to play these games with external controllers, or get an AV Famicom.

Edit: Not sure why your Zapper isn't working though, I have a similar adapter that Bratwurst made for me and it works fine on my setup.

[samson7point1]

Super Mario USA doesn't poll controller inputs from the extension port. Same for a few other Famicom games like Robot Gyro, a lot of games developed for the NES, and probably a good bit of hacks and homebrew.

You'd need to splice NES extension cords onto the internal FC controller inputs in order to play these games with external controllers, or get an AV Famicom.

Edit: Not sure why your Zapper isn't working though, I have a similar adapter that Bratwurst made for me and it works fine on my setup.

Aah, that's good to know. I didn't realize the expansion port wasn't literally connected to the same signal lines as the controllers. The odd thing about the zapper is that I have an older adapter that I made like 8 years ago with just the one port wired to the P2 signals including D3 and D4 and it does work. The only difference I can find in the wiring is that this new adapter I made does have slightly more resistance on the D3 and D4 lines - the difference between .7 ohms and 1 ohm. Maybe the extension cables I used are just such bad quality that they're degrading the signal?

[samson7point1]

Found the problem. Apparently that tiny variance in resistance was more significant than I thought. When I first assembled the adapter I must not have made the connections strong enough, they were able to register on the DMM and show ~1 ohm resistance but apparently not enough to get enough power to the Zapper. When I rewired it, I twisted longer strands and triple checked that the connections were completely saturated with solder. Resistance went down to like .7 or .8 ohms on each connection and all of a sudden the Zapper works fine.

[Bratwurst]

You'd need to splice NES extension cords onto the internal FC controller inputs in order to play these games with external controllers, or get an AV Famicom.

This is what I did, and also recommend. I decided I didn't care about 2P microphone functionality and dedicated those lines to what would be D3 & D4: https://i.imgur.com/ksf6dGl.jpg

[jd213]

Nice, I only bothered to splice in an extension cord for the Player 1 controller since I rarely have guests over nowadays, and my one friend who still likes to play NES games is more of a controller guy anyway.

I found that if you remove the little grey donut and shave a bit of plastic off of the hole in the FC case, the female port from the extension cord will slide in fairly nicely onto the back of the FC if you don't like having another cord hanging out of the back.

I also spliced the male end of the extension cord onto the FC controller, although apparently they need 2 resistors added: https://16bitgamer.canadian-forum.com/t ... -a-famicom