Cable Modem Troubleshooting: Motorola SB5120

Light patterns, images, manuals and more helpful info for the Motorola SB5120 cable modem –

Manufacturer: Motorola Model: SB5120
Modem Light Indicators

Flashing – Startup diagnostics in progress.
On – Cable modem is powered on.


Flashing – Scanning for a downstream channel.
On – Downstream channel is connected.

Send Flashing – Scanning for an upstream channel.
On – Upstream channel is connected.

Flashing – Scanning for a network connection.
On – Startup process complete. Modem aqcuired.


Flashing or On – Transmitting or receiving data.


This light turns on when the standby button is pressed and standby
mode is activated. If this light is on, all other lights will be off.
Notes and Useful Information:

Installation and User Manual (Requires Adobe Acrobat)
Motorola Product Website

19 thoughts on “Cable Modem Troubleshooting: Motorola SB5120”

  1. Pingback: Simplehelp » Cable Modem Index

  2. I have this Motorola cable modem. Does anyone know how I can put the modem into standby mode remotely. Is there a way I could put it to “sleep” after a set amount of time, like you would a TV or stereo.

  3. I have a Motorola SB5120 cable modem. I keep getting knock off line. I have to pull the power cable wait a few seconds and try again.

    Do I need a new Modem?

  4. how do i connect my motorola modem to my belkin wireless connection due to the fact theirs no cable to connected the tow from the shops is there an alternative?

  5. Hi i have an modem like this and my problem is that i can’t punt another PC on network only that pc if i put the cable on another PC it doesn’t connect please can you help me ?? !

  6. I need the adapter cube info for this item, I need to replace it, how is it configured i.e. polarity of center tip of female plu?
    Thank you

  7. I would like to know how to change from a usb connection to a ethernet connection…I have tried un pluging the modem to reset it and that didnt work.

  8. I’m looking for the link or whatever for the “user friendly online diagnostics page” that is advertised in all the materials for this modem. They seemed to have left out how to actually GET THERE, though… anyone know?

  9. I have a Motorola SB5120 cable modem. I keep getting knock off line. I have to pull the power cable wait a few seconds and try again.

    Do I need a new Modem?

  10. This modem only connects to the service provider and indefinite supplies one IP address per computer. If you use a computer and then want to connect another after, you have to switch off the modem and then switch it on again. Otherwise if you want to connect more than one computer at a time, you need a router. I personally have a Dlink wireless router. Hope this helps.

  11. Also you can connect two computers if one uses the ethernet connection and the other the USB connection.

  12. If you connecting another network device(hub, switch, router) another pc

    Remember to hard reset modem you have to do the following:
    Unplug power from Cable modem
    Unscrew Coax (TVcable) for 5 minutes (not 1, not 4 min)
    Screw the coax back, power on cable modem, wait for solid Online

    hope this helps….

  13. Alguien me regalo este modem y quisera saber como instalarlo a mi computadora, creo que necesito bajar algun software o algo. alguien me puede ayudar?

  14. Cable ISP Tech

    If you want more than one computer connected online, you will have to get a router.

    If you are having to power cycle(unplug -plug) the modem constantly, you either have a bad modem or your signal to the modem is bad. You will probably need to call your internet provider.
    There is no way to remotely shut down administer the standby button, unless you can remotely access the PC that the modem is connected to.

    Some ISPs will not let you connect both the Network cable and the USB connection simultaneously.

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