Yamaha FB-01 Service Manual page 9

Connection for MIDI Function Test
MIDI cable
(Unit being tested) (Standard unit © ) (Standard unit © )
Connection diagram for MIDI Function Test (Fig.2)
A "Standard unit" is defined as a properly functioning FB-01.
Three FB-01 units are required if the system channel test is to be performed.
FM Power Source (OPP: YM2164) and D/A (YM3012) Block Diagram
DAC INTERFACE D-GND + 5V