The next time this happens, place your hand on the power supply and try to determine if it is overheating. It should be slightly warm to the touch, but not hot. Hot would indicate that something in the keyboard is overloading the power supply and needs attention by a Yamaha Factory Service Technician.
If the power supply is defective, which is quite rare, you can test this out by connecting another, similarly rated power supply and see if the problem recurs. If it does, then the problem obviously lies within the keyboard's hardware and should be taken care of by a factory service authorized service center.
Good luck,
Gary
