That stinks.
Usually if I work on a system that has controller button issues but the problems are not related to faults with the controller board, it ends up being a faulty HU6280 CPU
You can test controller button functions directly from the CPU. Simply use a wire. One side of the wire soldered to ground somewhere(doesn't have to be ground on the CPU itself) then touch the other end to the pins for button functions to see if they work or not. Simply test each pin with the colored lines shown on the picture below to see if each one performs a button press when connected to ground. If one of the pins does nothing, well then it's a faulty HU6280 chip.
