We hava a Casio CTK-601 Synthesizer Keyboard. It was accidently left plugged in with a 12 volt adaptor. It uses a 9 volt adaptor. We do not know if it was having the following problem before or after this incident. Eight keys in the middle do not play and thirteen keys on the right end do not play. We have a manual and have read it. We tried turning off all power (unplugging and removing any batteries). Then hold down power button for approximately 20 seconds, then plugging adaptor back in and turning on power, to reset to factory default settings. The keys that would not play will then make a sound one time when pressed. The eight keys in the middle, are very low sounding and one of the black keys will occassionally hang up and keep playing until you turn power off and back on. The thirteen on the right end, will then play very loud and occassionally one of the black keys will hang up and keep playing until you turn power off and on. I have asked a music store about this problem and was told their technician could look at it for $80, and that is not including if he finds anything wrong and fixes it. I understand that the wrong voltage adaptor can destroy one. My friend just purchased it for $50, used as is at an auction. That weekend the keyboard was left plugged in. When my friend went to pick-up her purchase she discovered it had been left plugged in, and the adaptor was very hot and burned her hand unplugging it. We were told the keys were playing before and that it was probably something minor that we had to do to make them play, or either the contacts may need cleaning. Can you help or have any solutions or suggestions? I have researched for a service manual and found two, but not sure how hard a job it would be to tackle it ourselves, and we don't want to have to sink a whole lot of money in it if it is not fixable. We would appreciate a response. Thank you. Barbara, NC