Replacing an M120 DC Power Supply

In the DC power configuration, the router contains two DC power supplies (see DC Power Supply), located in the right rear of the chassis in slots PEM0 and PEM1 (left to right). A single DC power supply provides sufficient power for a fully configured router.

Each power supply (AC or DC) is hot-insertable and hot-removable.

Note: To maintain proper cooling and prevent thermal shutdown of the operating power supply unit, each power supply slot must contain either a power supply or a blank panel. If you remove a power supply, you must install a replacement power supply or a blank panel shortly after the removal.

Removing an M120 DC Power Supply

The power supplies are located at the rear of the chassis to the right of the CB1. Each power supply weighs approximately 8.4 lb (3.8 kg).

Caution: Do not leave a power supply slot empty for more than 30 minutes while the router is operational. For proper airflow, the power supply must remain in the chassis, or a blank panel must be used in an empty slot.

Note: After powering off a power supply, wait at least 60 seconds before turning it back on.

To remove a DC power supply:

1. Make sure that the voltage across the DC power source cable leads is 0 V and that there is no chance that the cables might become active during the removal process.
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.
3. Switch the circuit breaker on the power supply faceplate to the off position (O).
4. Remove the clear plastic cover protecting the terminal studs on the faceplate.
5. Remove the nut and washer from the terminal studs (see Figure 1). (Use a 3/8-in. nut driver or pliers.)

   Figure 1: Disconnecting Power Cables from the M120 DC Power Supply

   
6. Remove the cable lugs from the terminal studs.
7. Loosen the captive screws on the cable restraints on the lower edge of the power supply faceplate.
8. Carefully move the power cables out of the way.
9. Loosen the captive screw on each flange at the top and bottom of the power supply faceplate completely.
10. Grasp the handle on the power supply and pull firmly. Slide it halfway out of the chassis (see Figure 2).

    Warning: Do not touch the power connectors on the rear of the power supply (see Rear of the Power Supply Showing Midplane Connector). They can contain dangerous voltages.

11. Place one hand underneath the power supply to support it and slide it completely out of the chassis.

    Caution: Each power supply weighs approximately 8.4 lb (3.8 kg). Be prepared to support the full weight of the power supply as you remove it from the router.

Figure 2: Removing an M120 DC Power Supply

Installing an M120 DC Power Supply

To install a DC power supply (see Figure 3):

1. Make sure that the voltage across the DC power source cable leads is 0 V and that there is no chance that the cables might become active during installation.

   Caution: You must ensure that power connections maintain the proper polarity. The power source cables might be labeled (+) and (–) to indicate their polarity. There is no standard color coding for DC power cables. The color coding used by the external DC power source at your site determines the color coding for the leads on the power cables that attach to the terminal studs on the power supply faceplate.

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.
3. Switch the circuit breaker on the power supply faceplate to the off position (O).
4. Using both hands, slide the power supply into the chassis until you feel resistance.
5. Firmly push the power supply into the chassis until it comes to a stop. The power supply faceplate should be flush with any adjacent power supply faceplates.
6. Tighten the captive screws on the top and bottom flanges of the power supply faceplate to secure the power supply in the chassis.
7. Remove the clear plastic cover protecting the terminal studs on the faceplate.
8. Remove the nut and washer from the terminal studs.
9. Attach the lugs on the DC source power cables to the terminal studs, making sure the cables are not touching or in the way of any router components:
   • Attach the positive (+) DC source power cable lug to the RETURN (return) terminal.
   • Attach the negative (–) DC source power cable lug to the –48V (input) terminal.

     Note: For information about connecting to DC power sources, see M120 DC Power, Connection, and Cable Specifications.

10. Secure the power cable lugs to the terminal studs, first with the flat washer, then with the nut. Apply between 12 lb-in. (1.4 Nm) and 15 lb-in. (1.7 Nm) of torque to each nut (see Figure 4).
11. Loosen the captive screw on the cable restraint on the lower edge of the power supply faceplate.
12. Connect each DC power cable to the appropriate external DC power source.

    Note: For information about connecting to external DC power sources, see M120 DC Power, Connection, and Cable Specifications.

13. Switch the power switch on the power supply faceplate to the on position (|). Verify that the status LED on the power supply faceplate blinks, then lights steadily approximately one minute after you switch on the power switch.

Figure 3: Installing an M120 DC Power Supply

Figure 4: Connecting Power Cables to the M120 DC Power Supply