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Huffman, TX

Help with SB 5100 modem and comcast service

So I decided to stop paying comcast $7 to rent a modem every month and bought this SB 5100 on ebay. I got it switched over from the isp. It sorta works. It keeps going offline, sometimes for just a few minutes some times for long periods. The SB 5101 that comcast was lending me worked fine. All I did was swap all 3 lines from the back of the modem. So I'm pretty sure its not the cat 5 or the coax line.

If I check the modem status logs it has this error several hundred times.

2013-02-08 10:38:28 3-Critical D003.0 DHCP WARNING - Non-critical field invalid in response.
2013-02-08 10:38:19 3-Critical R002.0 No Ranging Response received - T3 time-out
2013-02-08 10:38:12 3-Critical R007.0 Unicast Ranging Received Abort Response - Re- initializing MAC

It has a few other errors that don't repeat as often.

2013-02-08 10:31:19 3-Critical T001.0 SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing
2013-02-08 10:31:19 3-Critical T002.0 SYNC Timing Synchronization failure - Failed to acquire FEC framing

Can anyone help me out as to what's going on or how to fix it? I have not tried to restore factory defaults or update the firmware, mostly because I can't find the firmware yet.

Irving, TX
Sounds like it might be a defective modem, or comcast doesn't ahve the MAC assigned correctly.


Huffman, TX
reply to isenhart
I think I figured it out. I moved the modem to the coax line that comes into the house, now it says online. Must have a bad connection. Weird that it only affects the older modem.

Ukiah, CA
reply to isenhart
said by isenhart:

I have not tried to restore factory defaults or update the firmware, mostly because I can't find the firmware yet.

Comcast automatically updates the firmware on supported modems that are connected to their network. There are no end-user firmware upgrades.


reply to isenhart
Did you happen to check your signal levels on the old modem compared to the new modem? Might have a bad coax port on the modem...

Chris 313
Come get some
Houma, LA
·AT&T U-Verse
·Comcast Digital ..
reply to isenhart
Comcast will be EOLing Docsis 2 modems like the 5100 sometime in late 2013 or into 2014 with the way the speed upgrades are currently going. So if you do have a bad modem, forget about ebay and buy from a known legit source. You took a chance with the used 5100 you bought. Hope you didn't pay too much for it.

These are 2 well known modems and are the current Docsis 3 tech, you'll also be future proofed, depending on how fast you wanna go right right off the bat:

» ··· le+modem

» ··· a+SB6141

There is also a new white version of the 6141, but the specs are the same except for small differences.