AT&T Network Adapter 25 Installation And Maintenance Manual page 243

Each power supply has one green LED on its front that can be seen through
the fan assembly. The LED is visible through the ventilation slots on the front
cover, but the cover must be removed for diagnostic and service purposes.
This LED is always lighted when the system is receiving 5.1 volts power. The
LED is dark when there is a failure in the +5 volt power supply or power
connections, or when there is a short on the backplane.
If the green LED on the power supply is dark, first make sure that the cabinet
is receiving ac power. Be sure that the fans are running, that the connection
to building ac power has been made correctly, and that the power rocker
switch is in the ON (1) position.
internal power connections (see Figure 4-8).
The power cord must be unplugged before the rear
Danger:
cover is removed. Simply setting the power switch to
OFF is not sufficient.
See DANGER below. Then check the
MAINTENANCE
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