Three button genesis controller. 

C button acts as the start button
start button does nothing 
b button works as it should 
a button does nothing
d-pad works as it should

i took this thing apart and it’s brand new inside. Took some isopropyl to the board contacts and rubber pads. No residue at all. 

Cord looks looks brand new. No bites, cuts or tears. It did have a bend in it right out of the controller shell. 

Any ideas? Thanks in advance. 

looks like the 3 button board has a 74hc157 multiplexer chip on it. I'd assume that's bad or isn't getting good inputs/outputs. you could try reflowing the solder but i'd replace it.