Rhodes Chroma Polaris

my polaris still wont play softly on channel one - turn off touch sensitivity and its fine.  Im trying to face the problem again.
--i have tried swapping all 5 socketed chips zx01 - zx05  and done the volume offset adjustment.No improvement. I am wondering what part of the main board takes the keyboard signal that seems on the schematic to have 'A' and 'B' contact  paths (apparently correlating to the regular and touch sensitive signals) and selects how they go to the 6 voices. and where do these A and B signals enter the voice channel. The schematic shows a section called 'channel control" with 4 chips [incl z79-78 and z31-32]. would this be involved, or would the trouble lie only within the single voice (channel 1)?And where do these 2 signals combine to be one sound?  any help to understand would be appreciated . Perhaps the problem is not in a socketed chip but even just a bad connection in the  path of either the A or B signal, but would this discontinuity  have to be in the  voice channel area?.
thanks for any ideas.