This article explains what is a SPMB? What are its functions? Can we RMA the SPMB alone?

root@re0> show chassis alarms no-forwarding
1 alarms currently active
Alarm time        Class Description
2024-06-23 22:23:08 PDT Major SPMB 0 Major errors

SPMB stands for Switch Processor Mezzanine Board.

• The CB sits between the RE and the chassis. It provides power to the corresponding RE and be a power controller for all the FRUs.
• There is an Ethernet switch (BCM8747) within the CB and it provides Ethernet connectivity between the RE (10GE) and the FRUs (1GE for the local SPMB and 1GE each FPC).
• The SPMB on the CB manages the SIB control and data path. There are PCIe links from the SPMB to the SIBs in order to control the TF ASIC and CPLD on the SIB.

In the show chassis hardware, you might see the SN# for SPMB as follows-

SPMB 0  REV 06  711-030686  EF3492  SNG PMB
SPMB 1  REV 06  711-030686  EF3439  SNG PMB

This doesn't mean that we can RMA the SPMB separately with the above SN#. SPMB is an in-built module inside the CB.
So, when you have to RMA the SPMB, you need to create the RMA for the corresponding CB.