There might be a need to replace a faulty CB due to an HW issue or to simply reseat the CB. This KB tells the steps to follow while replacing the CB on-site.

When CB failure is seen & below alarm is raised . Post troubleshooting found to be a hardware issue on CB 0 Need to proceed with replacement of the FRU.

Router_A> show chassis alarms
1 alarms currently active
Alarm time Class Description
2023-08-25 20:32:44 PDT Major CB 0 19.44 MHz clock failure

Step1: Take the host subsystem offline.

NOTE:

You can remove the SCB and Routing Engine as a unit, or remove the Routing Engine separately.

1. Determine whether the host subsystem is the primary or backup using the show chassis routing-engine CLI command. The output of this command will show whether the host subsystem is functioning as the primary or backup.
2. If the host subsystem is functioning as the primary, switch it to backup using the request chassis routing-engine master switch command.
3. On the console or other management device connected to the backup Routing Engine, enter CLI operational mode and run one of the following commands to take the backup host subsystem offline:

> request vmhost halt command if the Routing Engine supports VMHost.

> request system halt command if the Routing Engine does not support VMHost.

Wait until a message appears on the console confirming that the operating system has halted.

Step2: Take the SCB offline by issuing the following CLI command:

user@host> request chassis cb slot slot-number offline

Step3: Place an electrostatic bag or antistatic mat on a flat, stable surface.

Step4: Attach an ESD grounding strap to your bare wrist, and connect the other end of the strap to an ESD grounding point.

Step5: Rotate the ejector handles simultaneously counterclockwise to unseat the SCB.

Step6: Grasp the ejector handles, and slide the SCB about halfway out of the chassis.

Step7: Place one hand underneath the SCB to support it, and slide it completely out of the chassis.

Step8: Place the SCB on the antistatic mat.

Step9: If you are not replacing the SCB now, install a blank panel over the empty slot.

Installing an MX240 Switch Control Board

Step1: Attach an ESD grounding strap to your bare wrist, and connect the other end of the strap to an ESD grounding point.

Step2: Carefully align the sides of the Switch Control Board with the guides inside the chassis.

Step3: Slide the Switch Control Board into the chassis until you feel resistance, carefully ensuring that it is correctly aligned.

Step4: Grasp both ejector handles, and rotate them simultaneously clockwise until the Switch Control Board is fully seated.

Step5: Place the ejector handles in the proper position, horizontally and toward the centre of the board.

Step6: Check the LEDs on the Switch Control Board faceplate to verify that it is functioning normally.

• The green OK/FAIL LED should light steadily a few minutes after the Switch Control Board is installed.
• If the OK/FAIL LED is red, remove and install the Switch Control Board again. If the OK/FAIL LED still lights steadily, the

Step7: Check the status of the Switch Control Board using the " show chassis environment cb" command

Check if the RE is up, if not, try bringing the RE online by CLI, or reseat the RE.

In case Switch Control Board is still not functioning properly. Contact your customer support representative.