Chassis midplane
The following illustration shows the location and connectors of the chassis midplane.

| 1 PSU cage | 3 PDB connectors | 
| 2 Chassis midplane | 4 PSU connectors | 
1 PSU cage: For the PSU slots, see Chassis rear view.
2 Chassis midplane: For the replacement of the PSU cage and Chassis midplane, see PSU cage and chassis midplane replacement.
3 PDB connectors: When a node is installed in the chassis, the power distribution board (PDB) in the node is connected to the corresponding connector on the chassis midplane.
4 PSU connectors: When a hot-swap power supply unit (PSU) is installed in the PSU cage, the PSU is connected to the corresponding connector on the chassis midplane.
- The firmware of the chassis midplane can be updated via Lenovo XClarity Controller (XCC) and Lenovo XClarity Essentials OneCLI (LXCE OneCLI). Only the caretaker node can perform this update. 
- By default, the caretaker node is automatically selected by the PSoC firmware on the chassis midplane. To change the chassis caretaker preference, see Configuring the D3 Chassis. 
- Go to Update the firmware for more information on firmware updating tools.