Sony DFS-900M Operating Instructions Manual page 52

52
Installing Optional Expansion Boards
2
Remove the two screws (+B 4×8) securing the blank panel inside the
processor unit, and remove the blank panel.
3
Insert the BKDF-990 into the installation slot inside the processor unit, and
push it all the way in.
4
Using the two screws removed in step 2, secure the BKDF-990 to the
processor unit.