On my mega pad model 1850 only one button works

[grzegorzzyla]

I have 3 buttons A B C and START. Only 1 button works via the adapter. Interestingly, when I connect the quickshoot python joystick and set it to the SEGA standard, both buttons on the joystick work.
I looked at the controller diagram https://www.raspberryfield.life/2019/02/15/sega-mega-drive-genesis-3-button-abc-controller/ I have exactly the same model, only there is a different PCB, the direction contacts are on the same side as the buttons.
What is wrong?
I'll check that pad.