A common problem amongst Yamaha series electronic keyboards is the development of "dead keys" or "dead notes." This is mainly due to a build up of dust and debris between the key and its electronic contact point, thus disrupting the signal that creates each individual note sound. Cleaning the electronic contact point beneath a dead key will solve the problem. However, it's strongly advised that you seek professional assistance if you are not comfortable repairing electronics. Otherwise, prepare for a relatively challenging and time-consuming process.
Put on an anti-static device, without which you would be risking a potential circuit short due to the release of static electricity. Remove the plastic backing around the keys by unscrewing the several small Phillips screws securing it in place.
Detach the circuit board from its plastic mounting by unscrewing it to gain access to keyboard's internal circuitry and assembly. Gently place the circuit board out of the way.
Remove the main key assembly very carefully, be extra cautious not to not to damage or accidentally detach any small wires and circuitry attached. Carefully set the main key assembly aside.
Detach the rubber strip of small grey or black buttons found directly beneath the keyboard's keys from the keyboard's main circuit board to reveal a long strip of black contact buttons. Locate the damaged contact and gently pop out the small black contact button with a gently push of a finger.
Gingerly dip a cotton swab into 90 per cent isopropyl alcohol and clean the dead contact point. Note: now would be a great time to clean the rest of the contact points if you feel the need to do so.
Reassemble your Yamaha keyboard and test the dead key, it should now produce a sound. If the problem persists, take the keyboard to a certified technician.
Take digital pictures while you are disassembling your keyboard to help you remember the exact reassembly. For the best results, take your time, if you become uncomfortable during any stage of this process, relax and take it to a certified technician as you could cause more damage than having just a dead note.