Buttons not working on older game king

[bud0143]

I have a older 19” crt “big” game king. It doesn’t have the regular I/o cards. It has 3902 board. There is a board under monitor that I changed out. When you turn it on it boots as it should but only one button lights up and is active. So you can’t change games. Would my next check be to change out power supply? I did notice one red light inside power supply. Or should I replace motherboard/ backplane. The machine is at Friends house but I brought power supply home to check it. I know I can use s2000 power supply but forgot what pins to move. Thank you in advance

[bud0143]

so it ended up being the 3902 board.