remove the batterys and look for 1 to 4 screw holes. have a thin bladed knife to push in on the seam and to pry open. I start at the battery box side.. once apart you might have 1 or 2 small screws holding the curcit board down and some prongs to . Remove the srews and push the prongs to the side and pull off the board . you will be at the rubber button side. clean as much as possible. notice the inside of the buttons. you can use a pencil to draw on the inside to act as a conductor for the bad buttons that are worn