Product Overview 1-11
Overview of the Cisco 12008
If an overtemperature condition or a fan failure is detected within the router, the master
MBus module on the RP directs the MBus module on the clock and scheduler card (CSC)
to increase the operating voltage being delivered to the fan tray, causing the card cage fans
to run at “maximum” speed. This increases the volume of cooling air flowing through the
router.
If the increased fan speed does not alleviate the overtemperature condition in the affected
board, the MBus module on the board shuts down the bo ard’s power supply, taking the
board offline to protect it from thermal damage.
The MBus facility of the Cisco 12008 router is described in greater detail in the section
entitled “Cisco 12008 Environmental Monitoring Facility” on page74.
Power Supply Fa n Tray
The power supply fan tray is in the bottom of the power supply bays (see Figure1-2). This
fan tray maintains the temperature of the installed power supply(ies) within an acceptable
range.
Also designed for simplicity, the power supply fan tray incorporates four fans mounted on
a sheet metal carrier. The fan tray assembly contains associated wiring and a connector in
the back of the unit that enables it to draw operating power through the backplane from a
DC-DC converter on the CSC.
A captive installation screw mounted on the fan tray faceplate and guide rails in the sides
of the power supply bay facilitate insertion and removal of the unit. Once the unit is
inserted, you secure it in place by tightening the captive installation screw clockwise.
Similar to the card cage fan tray, the power supply fan tray is closely tied to the router’s
overall environmental monitoring system. If an overheating condition or a fan failure is
detected within the router, the voltage being delivered to the power supply fans by the CSC
is also increased, thereby causing the power supply fans to run at “maximum speed” to
increase the volume of cooling passing through the power supply bays.