Casio CZ/ VZ/ FZ - Pro Series

There is an adjustment you can make for the sensitivity 
of the CZ-1 aftertouch sensor. VR4 on the main board #MA1M, 
located on the upper right of the board. Fully counter
clockwise for maximum sensitivity, and clockwise for 
less sensitivity. Unless the sensor strip under the 
keyboard is shot, this should dial in the amount of 
aftertouch pressure you prefer.

Terry (The Casio Kid)