IBM 3270 Maintenance Manual page 309

The steps below describe how to move the fixed
disk adapter to the system unit while leaving the
fixed disk in the expansion unit.
1.
Set all work station Power switches to Off.
2. Remove the covers from both the system unit
and expansion unit.
3.
Remove the fixed disk adapter from the
expansion unit without removing the signal
cable from the adapter card.
4.
If you have two fixed disks, remove the signal
cable from the back of fixed disk D .
. CONTINUE
3-1700-22 Maintenance Information