AT&T 3B2 Maintenance Reference Manual page 91

Power
Each SCSI peripheral module (DCM, DM, TM) is equipped with an intelligent power supply
that automatically switches between input voltages of 120 and 240 volts AC for both domestic
and international applications. The SCSI XM power supply can be changed through an
inspection plate in the top of the supply. The SCSI 9-track tape drive power supply can be
changed by reversing a board inside the supply (see the Tape Drive Manual shipped with
unit). Both the SCSI XM and 9-track tape drive are ordered with the power supply set to the
desired voltage (120 or 240 volts).
As with other peripheral devices, SCSI devices should be connected to a reliable power source.
A
WARNING
Never remove power from any SCSI device while the system is powered up. This
includes removing power by external means or by operating the front-panel power
switch. An unexpected loss of power may cause loss of data on a SCSI storage device.
Soft Power
Each of the SCSI hardware components that have soft-power jacks are under power control of
the 3B2 computer. This means that when the 3B2 computer is powered up or powered down,
the SCSI devices are automatically powered up or down.
Most SCSI devices receive a soft-power signal through rear-panel soft-power jacks that daisy-
chain the signals from the 3B2 computer. An exception is the ESDI disk modules, that receives
soft-power signals through the 37-pin ESDI control cable from the disk controller module.
A
WARNING
The soft-power jacks on the rear panel of the ESDI disk modules are capped and
should not be used. Damage to the 3B2 computer will occur if a soft power cable is
connected to a DM/???E.
The SCSI 9-track tape drive cabinet has no soft-power jacks and, therefore, its power supply
has to be manually controlled.
382 Peripheral Overview 3-31