DEC 4000 Model 200 Operation Manual page 27

AC Present Indicator—The orange AC Present indicator lights
when the Power switch is set to on and voltage is present at the
input of the power supply. If the AC Present indicator does not
light when the Power switch is set to on, refer to your VAX 4000
Model 200 Troubleshooting and Diagnostics manual.
DC OK—When the green DC OK indicator is lit, the power supply
voltages are within the correct operating range. If the DC OK
indicator does not light when the Power switch is set to on, refer
to your VAX 4000 Model 200 Troubleshooting and Diagnostics
manual.
Fan Failure indicator—The amber Fan Failure indicator lights if
either of the two cooling fans stops working. The power supply
will automatically shut down the system as a precautionary
measure when a fan failure is detected. Call your Digital service
representative if a fan failure occurs.
Over Temperature Condition indicator—The amber Over
Temperature Condition indicator lights if the enclosure has shut
down due to an over temperature condition. Section 2.9 provides
instructions on recovering from an over temperature condition.
Power bus connectors—Three power bus connectors allow you
to configure a power bus for systems expanded with the R400X
or B400X expander. The power bus allows you to turn power
on and off for one or more expanders through the power supply
designated as the main power supply: this way, one power switch
can control power for an entire expanded system. Figure 1–11
illustrates a possible power bus configuration for an expanded
system.
NOTE: Dual-host systems should not be configured with a power
bus. Inadvertently shutting off a host system and bringing down
the cluster defeats the added reliability of a dual-host system.
The main out (MO) connector sends the power control
bus signal to the expander. One end of a power bus
cable is connected here, the other end is connected to the
secondary in (SI) connector of an expander power supply.
The secondary in (SI) connector receives the power bus
control signal from the main power supply. In a power
System Overview 1–17