This article explains recovery mechanism for MX304 FPC offline with reason as 'hard errors'

Below alarm will be seen and FPC may stay unresponsive:

root@lab-router> show chassis alarms no-forwarding

1 alarms currently active

Alarm time        Class Description

2024-05-20 01:28:21 UTC Major FPC 0 Hard errors

root@lab-router> show chassis fpc detail

Slot 0 information:

 State                Offline

 Reason               Unresponsive

 Total CPU DRAM          0 MB

 Total HBM             0 MB

 FIPS Capable            True

 Temperature           31 degrees C / 87 degrees F

 Max MPC base power consumption   0 Watts

 Max MPC total power consumption  0 Watts

PFE Information:

 PFE Power ON/OFF Bandwidth     SLC

 0  ON      800G

 1  ON      800G

 2  ON      800G

 3  ON      800G

 4  OFF      _

 5  OFF      _

Below are some of the solutions that can be tried:

1. Power cycle router to see if FPC comes online - it did not help in this case
2. Reseat of existing LMICs did not bring them online
3. Customer tried to bring FPC online without any LMIC in it and this confirms that this is chassis problem (since FPC is built-in)
4. New Chassis was replaced and existing LMIC was inserted in new chassis