IBM 9009-41A Manual page 30

Figure 13. Disconnecting the signal cable and the power cable
8. Ensure that all cables are carefully positioned out of the way, such that the disk drive backplane can
be easily lifted and removed.
9. Carefully unscrew the captive thumbscrew (A) of the disk drive backplane until fully loose as shown
in the following figure.
If needed, use a Phillips screwdriver to loosen the screws.
16 Power Systems: Power Systems: Drive backplanes