Sony DFS-900M Operating Instructions Manual page 46

To install function expansion boards
46
Installing Optional Expansion Boards
MV1 socket
MV2 socket
Use the following procedure to install function expansion boards.
1
Remove the four screws (+B 3×6) securing the board tray stabilizers, and
remove the stabilizers.
2
As shown in the figure below, push the levers on each end of the standard I/
O module to open them, and then pull the standard I/O module out.
Standard I/O module
DME1 socket
DME2 socket