Apple Xserve Intel (Late 2006) DIY Procedure for Power Distribution Board - Manual (Page 7)

Xserve (Late 2006) Power Distribution Board Replacement Instructions 
Drive Interconnect Backplane
Release the two locking levers on the front panel board cable connector and disconnect the
cable from the front panel board. Move the front panel board cable out of the way.
Disconnect the backplane-to-logic board I/O cable from the backplane.
Release the thumbscrew that secures the backplane to the enclosure.
Note: The thumbscrew is captive; you cannot remove it.
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