Sequential circuits samplers

Hello Again,

OK - i got my disk drive swapped out (thanx to the info provided
here) via a Sony model 
from eBay ($3.50 - not bad), but I am now facing the daunting task of
diagnosing/fixing 
the lack of velocity on about 8 keys. 
Starting with D4 (D in the 4th octave - counting from left to right),
I am seeing no velocity 
response for the next 8 keys. Do I need to pick up the service manual
(is this even covered 
in the service manual?)? Or does somoen here have expereience with
this? 
Thanx again to the Prophet Community,
James