The article explains On MX platforms, if a Minor alarm is reported for CB [x] for both Fabric chip reports an underlying issue with CB[x] and possible actions to be taken.

The MX Switch Control Board (SCB) provides Control Plane functions, Chassis management functions, and Switch Plane functions. It is also a carrier for the Routing Engine (RE).                
Each control board has two switch fabrics: SF0 and SF1. Each switch fabric has two fabric planes.
The alarm indicates all the planes under CB[x] are offline reports underlying issue with CB [x]

The below chassis alarm is reported during the issue time.

User@RE0> show chassis alarms no-forwarding

2 alarms currently active
Alarm time               Class  Description
2024-01-19 03:35:18 UTC  Minor  CB 1 Fabric Chip 1 Not Online
2024-01-19 03:35:18 UTC  Minor  CB 1 Fabric Chip 0 Not Online
 

User@RE0> show chassis fabric summary no-forwarding

Plane   State    Uptime
 0      Online   775 days, 19 hours, 7 minutes, 37 seconds
 1      Online   775 days, 19 hours, 7 minutes, 37 seconds
 2      Online   775 days, 19 hours, 7 minutes, 31 seconds
 3      Online   775 days, 19 hours, 7 minutes, 30 seconds
 4      Offline
 5      Offline
 6      Offline
 7      Offline



Chassisd logs:

Jan 19 03:35:17  acb_take_offline: CB 1, offlines, offlining planes
Jan 19 03:35:19  acb_offline_finish: fpm_atlas_set_cb_offline_led OFF all LEDs
Jan 19 03:35:19  i2cs_green_led_off: CB#1 - ok(green) LED turned off
Jan 19 03:35:19  power disable verified, CB#1

Messages logs :

Jan 19 03:35:17  acb_take_offline: CB 1, offlines, offlining planes
Jan 19 03:35:18  atlas_i2cs_fabric_active_led_off: CB#1 - active(blue) LED turned off
Jan 19 03:35:18  send: yellow alarm set, device CB 1, reason CB 1 Fabric Chip 0 Not Online
Jan 19 03:35:18  send: yellow alarm set, device CB 1, reason CB 1 Fabric Chip 1 Not Online
 

This could be a transient/ permanent Hardware issue with CB[X]
Kindly perform the below in a MW
 
From RE0 >> (here the alarm persist on CB 1)
 
request vmhost/system power-off other-routing-engine 
request chassis cb slot 1 offline
 
Verification :
show chassis environment cb 1
Wait for 1-2 minutes  

request chassis cb slot 1 online

Verification :
show chassis environment cb 1
show chassis alarm

Additional note:

If the CB1 does not go offline due to RE1 being online

Please halt the RE1 and then perform the CB1 offline action 
request system halt other-routing-engine 

request chassis cb slot 1 offline
 
Verification :
show chassis environment cb 1
Wait for 1-2 minutes  

request chassis cb slot 1 online

Verification :
show chassis environment cb 1
show chassis alarm

If the alarm does not clear even after following the steps, then contact JTAC Support for initiating an RMA for CB[x].