Sony DFS-900M Operating Instructions Manual page 55

3
Set pin 2 of the DIP switch under the flat cable to the "ON" position.
Note
Do not change settings of the other pins.
4
Insert the external device interface connectors board into its original slot,
and align the notches of the levers on both sides of the board to the left and
right sides of the slot mouth.
55
Connecting Up the Switcher