TurboGrafx-16 - for those of you who don't know about it...

[jperryss]

One site I found, but can't find now, was someone who made a NES controller work as a TG-16 controller, by using a chip. Handy as these controllers are quite expensive to replace.

This guy did a NES->Duo hack. The TG16 uses a different connector than the Duo does, but I'm sure he can point you in the right direction.
http://www.geocities.com/duo_r@sbcglobal.net/

[bacteria]

Found it! A mod to make a NES controller work on a TurboGrafx (TG-16): LINK and this I have an official TG-16 controller, taken it apart, going to use it; no sense buying extra components to mimic an official controller when I have the real thing!