The Passive Backplane; Figure 3-1: Detaching The Passive Backplane - Advantech AWS-8124T User Manual

3.1 The passive backplane

Four screws secure the 4-slot passive backplane to the inside of the
AWS-8124 chassis.
To service or replace the backplane, remove the top cover. There is
no need to slide the main chassis out. Remove the four screws that
secure the backplane to the chassis. Lift the backplane up and
remove the power cables.
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Figure 3-1: Detaching the passive backplane