Why are some of the keys not sounding?

I have an old Casio CA-100 keyboard and some of the keys stoped working. I took it apart and made sure everything was clean, some keys were broken but not in a way for there to be no connection to the circuit board underneath. After looking at the circuit board, and testing out each individual direct connection to the membrane. I still can’t figure out why some of the sounds aren’t working. When you touch some of the connections the speaker will cackle confirming they are receiving power but no sound, others aren’t receiving power at all.