Juniper M40E Hardware Manual page 179

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The rear subsystem include upper and lower impellers in the rear of the chassis. They
cool the SFMs, host module, PCGs, and power supplies. See "M40e Chassis Description"
on page 8.
The cooling system draws in room air through the air intake vent located at the front of
the chassis below the cable management system. After entering the chassis, the air
stream separates into separate flows for the front and rear subsystems, and the MCS
monitors the temperature of each flow independently. For a graphic depiction of the
airflow, see "M40e Cooling System Description" on page 48.
For the cooling system to function properly, the clearance around the chassis must be
sufficient for unobstructed airflow. See "M40e Clearance Requirements for Airflow and
Hardware Maintenance" on page 71.
During normal operation, the impellers and fans in the fan tray function at less than full
speed. The MCS constantly monitors the temperatures detected by sensors on the
midplane and router components, adjusting the speed of the fans and impellers as
necessary. If the router temperature exceeds the acceptable maximum, the MCS turns
off the power supplies. The following conditions automatically cause the fans and
impellers to run at full speed and also trigger the indicated alarm:
A fan or impeller fails (red alarm).
One of the impellers is removed (yellow alarm).
The router temperature exceeds the "temperature warm" threshold (yellow alarm).
The temperature of the router exceeds the maximum ("temperature hot") threshold
(red alarm and automatic shutdown of the power supplies).
For more information about impeller-related alarms, see "M40e Chassis and Interface
Alarm Messages" on page 147.
To troubleshoot the fans and impellers, follow these guidelines:
If the red alarm LED on the craft interface lights, check the LCD on the craft interface
for the source of the problem. The display reports the number of alarm conditions and
the source of each alarm, as described in "LCD Alarm Mode" on page 37. For a list of
messages, see "M40e Chassis and Interface Alarm Messages" on page 147.
Issue the following CLI command for more information about the source of an alarm
condition:
user@host> show chassis alarms
On a DC-powered router, if the blue LED labeled
supply faceplate, the airflow passing by the power supply might be insufficient. Place
your hand near the exhaust vents at the rear of the chassis to determine whether the
impellers are expelling air.
Chapter 15: Troubleshooting M40e Hardware Components
OUTPUT OK is blinking on the power
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