AT&T System 25 - Manual (Page 198)

MAINTENANCE
Removing and Restoring Power
When the following procedures are performed, the system must be
unplugged from the ac power source:
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Reseating or replacing the Service Circuit or CPU/Memory CPs
Replacing the frontplane ribbon connector between the Call
Processor and Memory CPs (Release 1 only)
Replacing the power supply
Replacing the fan assembly.
Danger: The System 25 cabinet(s)
This equipment must be
technicians.
.
Before removing power from one or
tape backup. To save translations,
Digital Tape Unit” in this section.
more
contain hazardous voltages.
serviced only by qualified
cabinets, save translations on
follow the procedures under “Using
the
the
To remove power from a cabinet, set the power switch on the rear panel of
the cabinet to the OFF (0) position. Unplug the cabinet power cord. When the
repair or replacement has been completed, restore power by plugging in the
cabinet power cord and setting the power switch to the ON (1) position. Note
that when power is removed from the first cabinet (contains the common
control circuits), the Emergency Transfer Unit automatically activates.
CAUTION: Removing a CP that is in use will cause users to be
disconnected.