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this problem occurs when the strips of the contact board are not installed properly try to re-install them on the main board, I hope it will resolve the problem of touch response, because the velocity sensor's circuit has some obstructions and you could also try to clean the strip's ends as well and try to install them thoroughly, and then tell if the problem resolves or not
sorry for delay in replytell me the detail of keys, I mean send me pics of the keys which don't make any sound so that I can figure it out.
i would love to help you but not here my email address is firstname.lastname@example.org me mail and then i'll tell you what to do
sorry I don't know about your digital piano because I never repaired it.
thanks for nice comment, and IF you detach all the keys and put them into hot water to let the glue melt on itself and clean the weights, after that (for reassembling) you can use any Polychloroprene Adhesive for the weights to stick back, I am not sure about the toxicity of the glue but I use gloves, glasses and be a lot more careful while using these kind of adhesives, and wash my hands, you can ask some carpenter or technician or better a doctor about the toxic effects before using it, I hope it helps.