base keyboard volume concern

Has enyone purchased a BASE (MODEL MK 962S) keyboard. the volume switch makes a clicking sound as the button is pressed to raise and lower the volume. How can I turn it off. It certainly spoils the instument. I am desperate. i am using it in a school production. Any help will be appreciated.I cannot even find the BASE keyboard sight.

.....maybe a workaround would be using a guitar volume pedal? just an idea or adjust it from a seperate mixer? hope this helps better late than never