Question about Arris SURFboard SB5120 Modem

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Motorola SB5120 Problem with ethernet cable

For some reason when the modem was installed the guy connected it to the CPU with a USB cord. Now we are trying to set up a wireless router so we need to use the ethernet cable.

There is internet connection for a few minutes with the ethernet cable, but then it is lost completely. We can't get a connection to hold with the ethernet cable even though the network card and all other hardware is working fine. This keeps happening after several re-boots and resets of the modem. What is going on!


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Re: Motorola SB5120 Problem with ethernet cable

My PC is connected to my modem with my USB. Because I had to setup up my router, I needed to go through my Ethernet port. What I discovered was that the port on the modem was damaged - pins were misaligned an ethernet cable was yanked out of the socket. I realigned the pins with a screwdriver and that worked, but it's not an ideal solution.

Posted on Jul 14, 2008

Re: Motorola SB5120 Problem with ethernet cable

This may sound like a cop-out lame answer but I assure you I don't think it it.


Specifically (if memory serves me) I believe my problem like that stemmed from a "root-kit" type of VIRUS. Swear to God this is true. I had even run an antivirus scan but it missed this problem. I dunno what OS and software you are using, but I had Windows 2000 Professional at the time and used AVAST Anti Virus (free) and it cleaned out all the lingering bad stuff. LIKE MAGIC my ETHERNET connectivity problem vanished!

You may have to do something like I did to clear it up - I downloaded AVAST on a healthy PC elsewhere and then burned it onto a CD and loaded it onto my ailing PC. 10 minutes later... ALL BETTER! :)

Good Luck,

Posted on Jan 02, 2008

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How to open settings of motorola SURFboard SB5120 modem?

Support for the Motorola SB5120, discontinued product, see next site:

Connecting the device, see the "Quick Reference Guide":

For installing the modem the easiest way is to run the provided cdrom.
When not available perform the settings as showed in the guides.

Motorola 5100 series user guide:

See page 7 "Before You Begin" for the requirements and selecting either USB or Ethernet connection.

Page 22 gives the overview for the pages how to configure ethernet settings.

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Certainly not. You just have to choose between the two.

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Unplug the power to the modem and the USB cable. Plug in Ethernet cable in computer and plug in the modem. Wait for WAN side of the modem to connect and stabilize. If your PC is already on, you should see the network connection appear in the task bar (if it's configured to show up). Open a command prompt. Type 'ping' and press Enter. You should get 4 ping responses from the modem which indicates that you LAN connection to the modem is functional.

Let me know if this doesn't work and I'll guide you through other methods to get it working.

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Most cable company's will not allow you to use the USB and the ethernet connection at the same time. You will need to only use ethernet to your PC and your XBOX. Once you have the ethernet cord connected from your modem to the WAN/Internet port on your router you will need to press the reset button on the back of the arris to authorise the router for access. After that is done you will plug you XBOX into 1 of the 4 numbered ports on the router. Then you will need an additional ethernet cord for your PC.

Hope this helps

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You can only use the USB connection or the ethernet connection to get it work.  It won't work on both.  
What type of router are you using?

Sep 13, 2008 | Arris SURFboard SB5120 Modem

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Need to hook up Belkin G wireless router to Motorola SB5120

Plug your cable line into your modem, make sure it's tight, but don't use a tool. Next plug the ethernet line from the modem to your PC ethernet port. Then plug in your power to the modem. Allow your modem to sync. Don't use the USB line at all. Do not even hook it up unless your computer doesn't have a working ethernet line. Don't run the disk either, it will only install the modem driver that is only used if you use USB.

If you have issues connecting after that, you may have to go into your ethernet adapter settings and make sure that it is using DHCP. DSL usually uses a different setting (PPP I think) and you will not be able to connect.

By the way, excellent choice in modems.

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