CM820A/NA: Troubleshoot Internet Connection

If Internet connection issues with the CM820 arise, troubleshooting may resolve the issue, or may provide insight as to what is causing the issue.  This document provides helpful information for troubleshooting Internet connection issues with the CM820.

The following troubleshooting steps are to be followed in sequence:

1. Check the physical connection
2. Verify the LEDs
3. Power Reset
4. Verify the cable signal

NOTE: If the solutions provided in this document do not resolve the issue, please contact the cable operator for assistance.

Check the physical connection

1. Verify that the CM820 power cord is connected from the power port of the CM820 to the power outlet.
2. Verify that the coaxial cable is connected from the cable port of the CM820 to the cable outlet.
3. Verify that the Ethernet cable is connected from the Ethernet port on the CM820 to the Ethernet port on the computer.
    

Verify the LEDs

With the proper setup, the Online and Link LED should be solid yellow or green.  If this is not the behavior that the CM820 is displaying, please refer to this table for more information regarding LED behavior.

Power Reset

1. Shutdown the computer.
2. Unplug the cable modem from the AC wall outlet and wait one minute.
3. Plug the cable modem into the wall outlet.
4. Wait until the Power, Receive, Send, and Online LEDs are solid.
5. Restart the computer.

Verify the cable signal

1. Launch a web browser, such as Internet Explorer, Firefox, or Safari.  Enter http://192.168.100.1 into the address box.  The Status page will appear.
    
2. In the Downstream section, verify Power levels are within the acceptable range of - 15 dBmV to + 15 dBmV for each downstream channel. 
   
   
    
3. In the Downstream section, identify the Modulation and Power to verify SNR levels are within the acceptable range for each downstream channel. 
   
   Acceptable SNR Levels (dB): 
   If QAM64, SNR should be 23.5 dB or greater. 
   If QAM256 and DPL( -6 dBmV to +15 dBmV) SNR should be 30 dB or greater. 
   If QAM256 and DPL(-15 dBmV to -6 dBmV) SNR should be 33 dB or greater.   
   
   
    
4. In the Upstream section, identify the number of Upstream Channels, Channel Type, and Symbolic Rate to verify thePower levels are within the acceptable range for each upstream channel. 
   
   Acceptable Upstream Power Levels (dBmV):
   
   
    

   Upstream Transmit Power Level
   Channel	US Channel Type	Symbol Rate	Acceptable US Power Level
   Single	TDMA	1280 Ksym/sec	+61 dBmV to 45 dBmV
   	ATDMA	2560 Ksym/sec	+58 dBmV to 45 dBmV
   		5120 Ksym/sec	+57 dBmV to 45 dBmV
   Two	TDMA	1280 Ksym/sec	+58 dBmV to 45 dBmV
   	ATDMA	2560 Ksym/sec	+55 dBmV to 45 dBmV
   		5120 Ksym/sec	+54 dBmV to 45 dBmV
   Three or more	TDMA	1280 Ksym/sec	+55 dBmV to 45 dBmV
   	ATDMA	2560 Ksym/sec	+52 dBmV to 45 dBmV
   		5120 Ksym/sec	+51 dBmV to 45 dBmV

5. Refresh the page at least twice to identify variations in SNR, Downstream Power, and Upstream Power.   
   
   NOTE: If the either of the signal levels are outside of the acceptable range, power cycle or factory reset the modem.  Factory resetting the modem will eliminate any customized settings.
    
6. Contact the cable provider to adjust the signal level to the acceptable level range.

Acceptable Signal Levels