You might see alarms for PSU down on the device being set and cleared multiple times in a day.

user@device> show chassis alarms no-forwarding

1 alarms currently active

Alarm time        Class Description

2023-05-02 01:08:38 EDT Major FPC 0 PSU 1 Output Failure

PSUs, or power supply units, are either removable or, in a few of the EX/QFX devices, are built-in. On most of the EX/QFX platforms, there is redundancy available for the power supply unit, so failure or impact on one PSU does not take the entire device down.

However, it is critical to keep all PSUs on the device in a Healthy state.

When PSU flapping is observed, the steps below can be taken to troubleshoot the issue.

Step-1:-  Monitor the LED status on the power supply unit. Below is an example of the LED status on a QFX5100 PSU



An amber color indicates a faulty PSU, and the PSU needs to be replaced.

However, as the issue is of flapping so there are chances that the led state when observed is either green or turned off in that scenario please follow the below steps.

Step 2:- Reseat the affected PSU and monitor for a few hours to check if the issue is resolved. Also, if available, replace the PSU with a spare unit. If the issue is not seen after replacing the PSU, then the PSU is faulty and needs a replacement. If a spare is not available onsite, then try swapping the PSUs and check if the alarm/issue moves to another PSU or stays in the same slot. If the Alarm moves, then the issue is still on the PSU, and it needs a replacement. However, if the alarm stays on the same PSU, then the issue is not with the PSU, and the steps below need to be followed to further troubleshoot the issue.

Step 3:-  If the issue is still seen, verify the External power source, and if possible, connect the affected PSU to an alternate power source and see if the issue is resolved. Also, ensure the power cable/adapters are verified as well in this step.

Step-4:- If the issue persists and the external power supply/Power cable/adapters are verified clean, then the issue is most likely on the chassis. As the issue can be a transient issue, please power cycle the device and check if the issue is resolved.

Step-5: If the issue is still seen, then the chassis needs to be replaced with an RMA.

Please ensure troubleshooting is done in a planned maintenance window and with Traffic/Services shifted away from the device, and open a JTAC case if any unexpected results/behavior is observed.
 

2024-03-04 : Article Created

2026-07-08: Grammar correction.