Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?


Troubleshooting the M120 Power System



Description: The power supply is not functioning properly.


  • If a red alarm condition occurs, issue the show chassis alarms command to determine the source of the problem.


    If the system temperature exceeds the threshold, the Junos OS shuts down all power supplies so that no status is displayed.

    The Junos OS also can shut down one of the power supplies for other reasons. In this case, the remaining power supply assumes the load, and you can still view the system status through the CLI or display.

  • If the power supply LED is off and no red alarm condition exists, check that the circuit breaker on a DC power supply or power switch on an AC power supply is switched to the on position (|).

  • Verify that the source circuit breaker has the proper current rating. Each power supply must be connected to a separate source circuit breaker.

  • If the LED is blinking, verify that the input voltage to the power supply is within the supply's operating range.

  • Verify that the power cord (AC) or power cables (DC) from the power source to the router are not damaged. If the insulation is cracked or broken, immediately replace the cord or cable.

  • Connect the power supply to a different power source with a new power cord or power cables. If the power supply LED still does not light, the power supply is the source of the problem. Replace the power supply with a spare, as described in Maintaining the M120 Power Supplies.

  • If the LED on the installed spare lights, the replaced power supply is faulty, and you should return it for replacement, as described in Returning a Hardware Component to Juniper Networks, Inc..

  • If you cannot determine the cause of the problem or need additional assistance, see Juniper Networks Technical Assistance Center.