[sdiy] CS70M aftertouch

[gm]

Currently working on a Yamaha CS70M with, among other problems, no 
response to keyboard aftertouch.
The service manual doesn't have much on this feature (other than a 
schematic of the sensor).
I need to understand how this is supposed to work.

It looks like there's a spring-mounted bar under the keyboard that is 
deflected out of position when pressure is applied;  this appears to 
deflect the metal plate mounted over the sensor.
With the keyboard in the upright position, I can manipulate this 
deflector to initiate the pressure-mod response;  it isn't working with 
the keyboard in the down position.

If someone who knows this unit could tell me the following:
--how critical is the angle of the deflector plate?
--how free is the spring-mounted bar supposed to be?  This one moves 
stiffly, and doesn't always return to original position.
--is there something else I should be looking at?
... I'd be most appreciative.

~GMM