Patches and discussion for Ensoniq VFX family

I just received the 2 service manuals (MR RAck + VFX)I ordered from
route66studios.com.
These manuals contain NO SCHEMATICS AT ALL and so are useless .
For exemple: they say : if you have syst code error, or bad sound kind
of pb=> change the mainboard !! do you believe this ? I could have
been an electronic specialist at ensoniq if the solution at any
problem encountered is : change the mainboard !! 
A french electronician which regularely deals with ensoniq material
such as MR Rack, told me that my pb was surely comming from the A/D
converter or operating amplifier (not sure of the translation). which
is a single piece that can  be change without changing the whole
mainboard !

fool