Interesting, I never knew about issues playung US HuCards on a PC Engine either.
So riddle me this, folks. I have a converter, made in Japan, that allows you to play TurboGrafx-16 cards on a PC Engine. I've never tried it, it seemed kinda senseless to me since just about every decent game produced in the US is already available on the PC Engine. So what's the deal? This thing won't actually work?
Perhaps I'll find out for myself. I have a PC Engine Duo in the store, the converter is there too...
Until you ground pin 29 of the Hu6280 chip nearly all games shouldn't work. I'm sure there are a few HuCARDs that will play without the mod, however, since there always seem to be at least a few exceptions to this stuff. Could be an interesting experiment to verify this here at Digital Press.