If Internet connection issues with the SB6121 arise, troubleshooting may resolve the issue, or may provide insight as to what is causing the issue. This document provides helpful information for troubleshooting connection issues with the SB6121.
This document contains the following sections, to be followed in sequence:
If the solutions provided in this document do not resolve the issue, please contact the cable operator.
- Checking the physical connection
- Verifying the LEDs
- Verifying the cable signal
- Power Reset
- Factory Reset
Checking the physical connection
- Verify that the SB6121 power cord is connected from the power port of the SB6121 to the power outlet.
- Verify that the coaxial cable is connected from the cable port of the SB6121 to the cable outlet.
- Verify that the Ethernet cable is connected from the Ethernet port on the SB6121 to the Ethernet port on the computer.
Verifying the LEDs
With the proper setup, the Online LED should be solid green, and the Link LED should either be amber or blue. If this is not the behavior that the SB6121 is displaying, please refer to this table for more information regarding LED behavior.
| ||Off||Flashing||Solid Green||Solid Blue||Solid Amber|
|POWER||No power to device||N/A||Modem is powered up||N/A||N/A|
|RECEIVE||Receive channel not found|
|Scanning for a receive (downstream) channel connection.||Downstream channel is connected.||Downstream channel is connected with bonded channels.||N/A|
|SEND||Send channel not found||Scanning for a send (upstream) channel connection.||Upstream channel is connected.||Upstream channel is connected with bonded channels.||N/A|
|ONLINE||Internet connection failed||Scanning for Network Connection||Connected to the Internet||N/A||N/A|
|LINK||No connection to the modem's Ethernet port detected||Transmitting or receiving data on Ethernet port||N/A||Computer is connected via a 10 mbps or 100 mbps Ethernet port||Computer is connected via a Gigabit (1000 mbps) Ethernet port|
Verifying the cable signal
- Launch a web browser, such as Internet Explorer, Firefox, or Safari. Enter http://192.168.100.1 into the address box. The Cable Modem Status page will appear.
- Click the Signal link on top menu. The Signal page will appear
- In the Downstream section, verify Power levels are within the acceptable range of - 15 dBmV to + 15 dBmV for each downstream channel.
- In the Downstream section, identify the Modulation and Power to find verify SNR levels are within the acceptable range for each downstream channel.
Acceptable SNR Levels (dB):
If QAM64, SNR should be 23.5 dBmV or greater.
If QAM256 and DPL( -6 dBmV to +15 dBmV) SNR should be 30 dBmV or greater.
If QAM256 and DPL(-15 dBmV to -6 dBmV) SNR should be 33 dBmV or greater.
- In the Upstream section, identify the Symbolic Rate to find verify Upstream Power levels are within the acceptable range.
Acceptable Upstream Power Levels (dBmV):
|Upstream Transmit Power Level|
|Channel||US Channel Type||Symbol Rate||Acceptable US Power Level|
|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|
|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|
| 2560 Ksym/sec||+52 dBmV to 45 dBmV|
| 5120 Ksym/sec||+51 dBmV to 45 dBmV|
- 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.
- Contact the cable provider to adjust the signal level to the acceptable level range.
Acceptable Signal Levels (per channel)
|Recommended Max Downstream|
Power Level (DPL)
|Recommended Min Downstream|
Power Level (DPL)
|+15 dBmV||-15 dBmV|
|Downstream Signal to Noise Ratio (SNR)|
|Modulation||Downstream Power Level||Acceptable DS SNR|
|64 QAM||n/a||23.5 dB or greater|
|-6 dBmV to +15 BmV||30 dB or greater|
|-6 dBmV to -15 dBmV||33 dB or greater|
|Upstream Transmit Power Level|
|Channel||US Channel Type||Symbol Rate||Recommended Max US Power Level||Recommended Min US Power Level|
|Single||TDMA||1280 Ksym/sec||+61 dBmV ||45 dBmV|
|ATDMA||2560 Ksym/sec||+58 dBmV ||45 dBmV|
|5120 Ksym/sec||+57 dBmV ||45 dBmV|
|Two||TDMA||1280 Ksym/sec||+58 dBmV ||45 dBmV|
|ATDMA||2560 Ksym/sec||+55 dBmV ||45 dBmV|
|5120 Ksym/sec||+54 dBmV ||45 dBmV|
|Three or more||TDMA||1280 Ksym/sec||+55 dBmV ||45 dBmV|
|ATDMA||2560 Ksym/sec||+52 dBmV ||45 dBmV|
|5120 Ksym/sec||+51 dBmV ||45 dBmV|
- Shutdown the computer.
- Unplug the cable modem from the AC wall outlet and wait one minute.
- Plug the cable modem into the wall outlet.
- Wait until the Power, Receive, Send, and Online LEDs are solid.
- Restart the computer.
- Disconnect the coaxial cable.
- Power cycle the unit by disconnecting the power cord for 10 seconds, then reconnect the power cord.
- 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.
- Click the Configuration link on top. The Configuraton page will appear.
- Click the Reset All Defaults button (as shown below).
- When asked, Do you want to proceed?, click the OK button. The modem will reset to it's factory state, and will go through the initialization process.
- Connect the coaxial cable to the modem.
NOTE: The initialization process may take 5 to 30 minutes.