Place a 4-inch piece of masking tape, sticky side up, on your work bench. Carefully remove all screws holding the digital piano housing in place and stick them onto the tape to keep them from rolling away. Remove the cover and set it aside.
Curl your finger under the far end of the key. Slowly slide the key off of the piano. Set it upside down on a soft surface so you do not scratch the top of the key.
Locate the key weight and remove it from the key. It might slide off easily, but you may have to pry it out with a flat head screwdriver. Clean the adhesive residue off the bottom of the piano key and the weight.
Use the coarse sandpaper to roughen the side of the weight where you will apply the adhesive. Apply the gel superglue to the underside of the piano key and use the tweezers to slide the weight back onto the key in its proper place. Allow to dry for about 10 minutes.
Use the plastic safe contact cleaner to clean the spot underneath the key where it contacts the digital message board. Even a small speck of dust on the contact can cause sound distortion.
Slide the key back into place on the keyboard, replace the housing and replace the screws.