Each Emax voice runs through its own SSM2047 combined VCF/VCA — see the Output Channel schematic (IC30) in this archive. A dead or misbehaving single voice usually traces to its analog back end.
Diagnosis: play a held note and sweep cutoff while scoping the voice output along the schematic chain (6012 DAC -> SSM2047 -> output amp). If the DAC node is moving but the post-filter output is silent or will not sweep, suspect the SSM2047 or its supporting parts. Confirm the +10 V and -12 V rails at the chip first.
SSM2047s are obsolete; NOS chips or a pull from a donor board are the usual fix. Verify everything against the service-manual schematics before desoldering. (Community-sourced procedure — verify for your board revision.)