Problem with direcional on games.

the resistors on the side are all "pull ups", that make that when the input is not grounded (like moving the stick) at bit level it returns (1) , when you move the stick UP, the joysticks grounds the line, so it reads (0), there is two things, as you already changed the little board, it is obvious a problem in the mainboard

can be some big problem like the input at the engine just broken (doing short circuit to ground).

but can be some tiny problem like the track just cutted (open circuit), so the "open collector pin of the engine don't receive the pull up voltage"

ah checks also the wiring. with a continuous meter

there is can be have a discharge of static electricity at the time of the solder to make repairs
when the plate of the joystick is removed the test gives it always the movement has one ?
check the wire and sold on the main board and clean it with a solvent

I left only the joystick board to repair. So i don´t think that some static may caused mal fuction. I purchased this msx on march 2011 and this problem already exists.

that is because now without that board attached, any line UP DOWN LEFT RIGHT, has NOT its PULL UP resistente to +5v.... so the software understand &B0000 = something to do ...

and by that reason that is not a proof that it is the joystick little board. Because now, all the lines behaves like the broken one.

Understood.