The microprocessor knows what function to do when pressing a key, for the voltage that reaches the pin of the key, for each function there will be a different voltage, this voltage difference is determined by the resistance value, which corresponds to each fabric, one side is ground and the other to a power supply, limited by a resistance, for each key it will be a different resistance value, this gives us the potential difference, I must check that that resistance is not altered, even if it is well, then proceed to alter that value slightly up or down, until you give the chanel function more, since as you replaced the swich, they are discarded .... greetings.