Hi sam,
I see that you are having issues with your Yamaha Keyboard.
Well that is a nice Gift still it is the thought that counts right, but this Keyboard has been discontinued in the market.
Regarding the Fix there are no manuals online that can help with your concern, try going to this site where you can get service center location near your area, just enter you Zip code then it should show you details of where you can have it checked click this
LinkI hope that this will help.
Thank you for choosing Fixya,
mvincentc