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[MX] Minor alarm 'SFB Voltage Sensor Out-of-Range'



Article ID: KB36383 KB Last Updated: 26 Dec 2020Version: 1.0

This article explains how to troubleshoot ‚Äčthe following chassis alarm on Juniper MX devices:

SFB Voltage Sensor Out-of-Range

This minor alarm may not be is an issue with the SFB. Be sure to check logs for any PEM related issues as well.

In some cases, there may be a power supply module (PSM) outputting a voltage that is out of the range/tolerance limit for certain chassis components. This would trigger a minor alarm for the component as well as the PSM. However, in other cases the alarm for the PSM would clear, but not for the component.

show chassis alarms          
1 alarms currently active
Alarm time               Class  Description
2018-10-10 17:50:05 UTC  Minor  SFB 2 Voltage Sensor Out-of-Range

For example, there is a minor alarm for SFB 2 voltage sensor out-of-range.However, when checking the log messages, an issue is seen with the PSM module 10 which got cleared.

Oct 10 17:28:14  re0-jtac-lab chassisd[15349]: CHASSISD_PEM_VOLTAGE: Power supply 10 reports problem; check output voltage
Oct 10 17:28:34  re0-jtac-lab alarmd[16982]: Alarm cleared: PSM color=RED, class=CHASSIS, reason=PSM 10 Not OK
Oct 10 17:28:34  re0-jtac-lab craftd[15352]: Major alarm cleared, PSM 10 Not OK

After this, there was an alarm for SFB 2 voltage sensor out-of-range: 

Oct 10 17:40:01  re0-jtac-lab spmb0 cmty_sfb_voltage_check_one : sfb-03-SFB2-Bias-5V voltage outside tolerance!
Oct 10 17:40:01  re0-jtac-lab spmb0 Expected range (4500 - 5500)  read value: 5554
Oct 10 17:40:05  re0-jtac-lab alarmd[16982]: Alarm set: SFB color=YELLOW, class=CHASSIS, reason=SFB 3 Voltage Sensor Out-of-Range
Oct 10 17:40:05  re0-jtac-lab craftd[15352]:  Minor alarm set, SFB 2 Voltage Sensor Out-of-Range

Therefore, the SFB alarm is a victim and not the cause. In order to clear the alarm, physically reseat or replace the PSM module that reported the problem in the first place.

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