Dell PowerEdge 6850 System Installation Manual page 16

12. Place the two slide switches on each side of the chassis in the unlocked position to release the chassis crossbar, then lift up the crossbar and remove it.
See Figure C-6.
Figure C-6. Removing and Installing the Chassis Crossbar
13. Disconnect all data interface cables, the chassis intrusion switch cable, and the RAID battery cable (if applicable) from the system board.
14. Disconnect the power distribution cable harness from the system board.
The power distribution cable harness and the side of the chassis have Velcro pads to hold the cable harness in place while you remove the system
board. Bend the cable harness straight up and secure it to the side of the chassis. See Figure C-7.
Figure C-7. Securing the Power Distribution Cable Harness