In the MIXER section:
- set both OSC 1 and OSC 2 on
- make sure the levels for OSC 1 and OSC 2 are turned up (12 o'clock for both is a good starting point)
In the OSCILLATOR 2 section
- set DUO MODE on
- set KB CTRL off (both LO and HI lights being off)
- set OCTAVE and FREQUENCY to the desired drone note
Playing the keyboard should now give you a drone note (OSC 2) and a melody note (OSC 1).