Fixing Key which is no longer sensitive to touch pressurehich sound is always full strength loud

I have had a Williams Allegro (v 2) for some years and it works very well. However recently three of the ‘black’ notes are no longer sensitive to key pressure and always sound at maximum volume. I remember a number of years ago having the same problem and after getting some advice (which involved opening the keyboard and working on it) I fixed it. However I can no longer remember what I did. I would be most grateful if someone can advise me on this.

I want to correct the typographical error in my topic TITLE
Fixing key which is no longer sensitive to touch pressure, in which sound is always full volume irrespective of the pressure. .