yamaha u3silent problem

hi
i dont know if anyone here can help me but any advice is apreciated
i have u3 silent the acoustic part works very well but all b notes dont work and some c#
i dont know why i asked a technician a tuner who opened the lid there was a red laser beam which pssed from right side to left side throgh a metal piece with a cledt for every note if any object cut the laser beam there was sound he cleaned them with cotton and temporarily the problem solved but after several weeks the problem returned
thank you for help

hi
no digital expert here?

No, this forum is for acoustic pianos. Go back to the Forums page and choose the Digital Piano Forum.

ok
thank you