Yamaha MU80 Owner's Manual page 31

Operation
1 Use the PART q buttons to select Part 2.
P a r t 2 .
2 Use the SELECT w buttons to call up the "Rcv CH" display
below.
3 Use the VALUE q buttons to change the MIDI Receive Chan-
nel to "A01."
4 Finally, use the SELECT w buttons to move the arrow cursor
back to the instrument icon (so that the Voice name is displayed),
and play the MIDI keyboard again.
Both "level meter" move together.
If both Parts 1 and 2 have been set to MIDI channel 1, both of their "level
meters" should move together as you play. And, if the two Parts are set to
different Voices, you should hear two different Voices sound at the same
time. (To change the Voice for a Part, refer back to Selecting Voices above.)
Current MIDI Receive Channel.
GUIDED TOUR
2 1