Replacing a PCG in an M40e Router
During normal operation, both PCGs generate a 125-MHz clock signal, but only one is designated as the master. The modules and ASICs in the Packet Forwarding Engine that use the clock signal to gate packet processing use only the signal from the master PCG. For information about determining which PCG is the master, see Maintaining the M40e PCGs.
PCGs are hot-pluggable, as described in M40e Field-Replaceable Units (FRUs). Removal or failure of the backup PCG does not affect router function. If the master PCG fails or is removed from the chassis, however, the Packet Forwarding Engine resets so that the components start using the signal from the other PCG (which becomes the master). The Packet Forwarding Engine cannot accept incoming packets until each PFE component, including the SFM and FPCs, resets to recognize the new master PCG. This can result in traffic halting for several minutes.
Removing a PCG in an M40e Router
To remove a PCG (see Figure 1):
- Place an electrostatic bag or antistatic mat on a flat, stable surface.
- Attach an electrostatic discharge (ESD) grounding strap to your bare wrist, and connect the strap to one of the ESD points on the chassis. For more information about ESD, see Preventing Electrostatic Discharge Damage to an M Series, MX Series, or T Series Router.
- Remove the rear component cover by loosening the thumbscrew at each corner of the cover and pulling it straight off the chassis. For complete instructions, see Reinstalling the M40e Components into the Chassis.
- Press and hold the offline button on the PCG faceplate
until the yellow LED labeled FAIL lights, which takes about
3 seconds.
(Keep in mind that if you are removing the master PCG, forwarding halts while the Packet Forwarding Engine resets so that the components start using the clock signal from the other PCG, which becomes the master.
- Loosen the thumbscrew at the lower right corner of the PCG faceplate, using a Phillips screwdriver if necessary.
- Grasp the thumbscrew and slide the PCG about halfway
out of the chassis.
Caution: Be careful to slide the PCG straight out of the chassis to avoid bending any of the pins on the underside of the board.
- Place one hand under the PCG to support it, slide it completely out of the chassis, and place it on the antistatic mat or in the electrostatic bag.
Figure 1: Removing a PCG
Installing a PCG in an M40e Router
To install a PCG (see Figure 2):
- Attach an electrostatic discharge (ESD) grounding strap to your bare wrist, and connect the strap to one of the ESD points on the chassis. For more information about ESD, see Preventing Electrostatic Discharge Damage to an M Series, MX Series, or T Series Router.
- Place one hand under the PCG to support it and grasp the thumbscrew on the faceplate with the other hand.
- Align the rear of the PCG with the guides inside the chassis and slide it in completely.
- Tighten the thumbscrew on the faceplate to seat the PCG firmly in the chassis.
- Verify that the green LED
labeled OK lights steadily, which takes about 3 seconds.
You can also verify correct PCG functioning by issuing the show chassis environment pcg command, as described in Maintaining the M40e PCGs.
- Reinstall the rear component cover and tighten the thumbscrew
at each corner to secure it to the chassis. For complete instructions,
see Reinstalling the M40e Components into the Chassis.
Caution: To maintain proper airflow and provide electromagnetic shielding, do not operate the router without the rear component cover in place.
Figure 2: Installing a PCG
