Description

This article describes the issue of the "PEM x Dipswitch 1 Feed Connection 1" alarm being generated, when the switch position of the MX960/SRXHE/EX9200 High Capacity DC PEM DIP device is set to 1.

 

Symptoms

For an MX960/SRX HE/EX9200 High Capacity DC PEM with two feed inputs selected (DIP switch in position 1), having input power only on one feed will generate the following alarm in the chassis:

user@router-re1> show chassis alarms
1 alarms currently active
Alarm time Class Description
2013-05-30 15:34:03 UTC Major PEM 2 Dipswitch 1 Feed Connection 1 <
user@router-re1>

Solution

For MX960, each High Capacity DC PEM will accept two DC feeds (labeled as INP0 and INP1). It is possible to operate with one feed, but with lower power output. The DIP switch on the PEM is near the on/off switch. This DIP switch should be set according to the number of DC feeds that are present for the PEM.

  • Position 0: Indicates that only one DC feed is provided

  • Position 1: Indicates that two DC feeds are provided

When two feeds are expected by the PEM (the DIP switch is in position 1) and only one input has power, you will see the "PEM X Dipswitch 1 Feed Connection 1" alarm. To clear the alarm, you must identify the cause of the alarm and resolve it.

NOTE: Flipping the DIP switch will not impact traffic. However, it is recommended to do so in a maintenance window to guard against unforeseen circumstances.

 

The following image illustrates the DIP switch (Input mode switch):

alt

 

The following example illustrates the alarm.

 

The PEM 2 DIP switch was set to position 1 and one input feed had no power; the alarm was generated and the PEM capacity is displayed as 1700W:

user@router-re1> show chassis alarms
1 alarms currently active
Alarm time Class Description
2013-05-30 15:34:03 UTC Major PEM 2 Dipswitch 1 Feed Connection 1
user@router-re1> show chassis power

PEM 2:
State: Online
DC input: Check (2 feed expected, 1 feed connected)  <<<< The DIP switch is in position 1.
DC input: 48.0 V input (58000 mV)
Capacity: 1700 W (maximum 4100 W)
DC output: 174 W (zone 0, 3 A at 58 V, 10% of capacity)

 

When PEM0 DIP is in position 1, then there is no alarm:

"show chassis power" shown - DC input: OK (2 feed expected, 2 feed connected)
===================================================================================================
user@router-re1> show chassis power

PEM 0:
State: Online
DC input: OK (2 feed expected, 2 feed connected) < When the DIP switch in position 1.
DC input: 48.0 V input (57500 mV)
Capacity: 4100 W (maximum 4100 W) < Capacity is 4100W
DC output: 969 W (zone 0, 17 A at 57 V, 23% of capacity)
user@router-re1>

 

Note for troubleshooting DIP switch issues:

  • When the DIP switch is in position 1 with two feeds connected and the alarm is seen, you would need to troubleshoot further to understand the cause for the alarms such as problems with circuit breakers and feeders or verify whether it is a real hardware issue.

  • Monitor the time of alarm generation, compare it with the system uptime, and assess whether the issue has been present from day 1 or has manifested due to recent failures.

If there is only one power feed for the PEM, move the dipswitch to position 0.

NOTE: Flipping the dip switch will not impact traffic. However, it is recommended to do so in a maintenance window to guard against unforeseen circumstances.

Check the power feeds to the PEM that is generating the alarm:

  • Make sure that the power leads are properly secured to the PEM inputs.

  • Make sure that there is power to both leads.

  • Make sure power cables are in good state and swap if needed.

  • Make sure that no circuit breakers have tripped or fuses blown in the facility DC circuits. Reset circuit breakers if needed.

CAUTION: The above steps should be performed only by someone trained and qualified in DC power operations.

If neither of the above steps resolves the alarm, open a case with your technical support representative to investigate the issue further.

For more detailed information, refer to KB75896 - [MX960/MX10K] "PEM X Feed X switch OFF but input connected" alarms [juniper.net].

Modification History

2024-02-09: Added a reference KB link (KB75896 [juniper.net]) in Solution
2023-12-05: Added note for troubleshooting DIP switch issues

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