Sony DFS-900M Operating Instructions Manual page 61

Note
Do not turn off the power switches during shutdown processing. If you turn
off the power before the shutdown finishes, the switcher may become
unable to boot normally.
3
Turn off the POWER switch (when using the BKDF-901) or the POWER
switches A and B (when using the BKDF-902) on the rear panel of the
control panel.
4
Turn off the POWER switch on the processor unit.
61
Connecting Up the Switcher