Old thread I know but maybe this info is helpful to someone..?
I still cant quite believe Nintendo tried to region lock all accessories No other company before or since has done this AFAIK. Even Nintendo's video cables were specifically altered for PAL markets.
Just alittle extra info - Nintendo stopped using the 'controller lockout' in about 1994, and PAL SNES consoles made after that usually work fine with US/Japanese controllers with no alterations needed (Although ironically these PAL SNES's are usually much more difficult to 50/60Hz mod)
Oh, and if anyone here happens to have a picture of the rear of a US NES controller port board I would love to see it for comparison...
The US NES doesn't have controller port boards. The pins connect (via wires of course) to the connector on the console main board.
For what it's worth... I think the diodes used in the controller lines for European NES consoles may have been to do with a legal requirement relating to EM/RF interference protection, or maybe some kind of safety feature. Because PAL NES consoles sold in other regions (specifically the Hong Kong version NES) have no controller port boards, just like US NES consoles, and use US-type NES-004 controllers.