hey -i found the link-

http://sounddoctorin.com/synthtec/parts/key.htm


" Oberheim Matrix 6 As you can see, this is totally identical to Kawai K3 without weighting. The weights can be removed usually from those keys with ease in a pinch. Or not someone said. Possibly Kawai upgraded the glue job. One can always use them in a less used place with a shortened spring I suppose w/out pulling the weight out. "