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Cisco uBR905 Router Hardware Installation Guide
OL-0598-01 (9/2000)
Chapter 4
Troubleshooting
Troubleshooting Subsystems
Coaxial Cable Subsystem
For proper operation, the Cisco uBR905 router must be able to establish a connection with the service
provider’s CMTS. There are many conditions inherent to coaxial cable that can inhibit this connection:
Step 1
Verify the cable connection from the router to the HFC plant and headend by checking the video
reception. You should test the same coaxial cable that the router is connected to—if necessary,
disconnect the router from the coaxial cable and connect a cable-ready TV in its place.
If the TV does not receive any cable channels, contact the service provider to re-establish service to the
site. If the TV does receive cable channels, it indicates that the basic infrastructure between the site and
the HFC plant and headend is working; however, because data connections are much more sensitive to
signal interference than cable TV service, it is still possible that a problem exists that prevents reception
of the data signals.
Step 2
If you are using a splitter or coupler to share the coaxial cable between a TV and the router, remove the
splitter or coupler, TV, and any other devices connected to the cable (such as video or DVD players) so
that the router connects directly to the coaxial cable coming out of the CATV wall outlet. Make sure
that the router is the only device on this segment of cable.
If the router functions in this configuration, inspect the splitter and any other devices that were installed
on this cable segment. If necessary, upgrade them and their interconnecting cables with ones that have
higher-quality connectors—see “Coaxial Connector and Cable Specifications” in Appendix B,
“Connector and Cable Specifications” for the recommended cable and connector quality. A high-pass
filter might be necessary between the modem and TV to prevent signal interference. If this does not
help, you might need to install a separate cable for TV reception.
Step 3
Disconnect the coaxial cable from the back of the router and inspect the cable and its connector. Is the
center conductor on the coaxial cable end straight and of the correct length to ensure a good connection?
If the center conductor is not straight or appears to be too long or too short, cut the coaxial cable behind
the connector end, and strip the insulation back. Make sure that the newly exposed center conductor is
straight. Before replacing the new cable connector end, check the general condition of the cable. Make
sure that the new conductor end is securely crimped to the cable.
Note
The center connector should extend 1/8 inch (3.2 mm) beyond the end of the connector.
Step 4
Is the coaxial cable running to the router in excellent condition?
The coaxial cable between the router and the cable tap must be of very high quality. The cable insulation
must be at least 80 percent braid with foil. If the existing cable appears to be of lesser quality or in poor
condition, replace the cable from the ground block or tap to the cable end.
Step 5
Is the coaxial cable connection to the back of the cable access router secure?
Check that the coaxial cable end is securely screwed onto the F-connector at the back of the cable access
router. Hand-tighten the connector, making sure that it is finger tight; then give it a 1/6 turn.
Note
If you are unable to resolve the problem, contact your internal service organization for
instructions and assistance.
