After a normal power up, press 4,5, 6 together to enter the scanner diagnostic. Press a key down slowly. say C4. It will first display the the first contact with C4, then the second contact with another C4 and then it should start showing MONO PRESSURE expressed as 1 to 256. I use the feel and common sense here. You want zero to 256 without excessive pressure. Check both sharps and naturals in several areas. If it takes excessive pressure to hit 256, a gain adjustment for each pressure strip is available.
To adjust differently, R17 is for the natural keys and R15 is for the black key. Both are located on the Player Control PCB, assy 121077. Turning either pot increase the gain of the op-amps connected to each mono pressure strip. More gain, the less pressure needed to get to 256.
These adjustment are at the machine level and done to calibrate how much pressure is needed to get from zero to 256.
Pressure can also varied in software setting in the master menu. You can also use the MIDI Scope in the Master/utility menu to view the MIDI values. They vary 0 to 127. I would do a hard reset before any testing, and to ensure the default mono pressure setting is selected before you do any tweaking.
Do you need a copy of the service manual?