Two keys on the Yamaha P-150 are "hanging". I could open the P-150. The task is to replace those 2 keys: I ordered two keys in USA by Syntaur. All the tutorial YouTubes replacing keys in Yamaha Keyboards or Digital Pianos are different to the P-150. In another post, someone tell us, that all the keys should have to taken out for working from the back. Is this necessary?