[Wlug] Test needed on declared-ill Modem. Who has a lab?

E Johnson iris.gates at gmail.com
Thu Sep 27 10:36:34 EDT 2012

I don't know how much of the recent comments are directed to me, or which
were responding to Richard.

This here:

> Make sure that you update the MAC address with charter, and that
> they actually update it. I've had a few problems where they
> haven't even though they said they did.

Yes! That happened to me, and the modem had to be re-registered two or
three times. It depends on the tech you talk to. My modem was incorrectly
or incompletely registered here by the install tach on the day the service
was hooked up. The internet generally worked as it should anyway, but
during times when there were connectivity problems here (see below), in
phone calls to tech support, every once in a while the tech would tell me
"I" had the wrong MAC address, that I was running an unauthorized modem,
etc.. Then I would have to explain why that seemed to be, and they would
try again to get that corrected.

My history here:

Charter here needs a DOCSYS3-compliant modem. I was running a Motorola
SB6120, which worked fine for 27 months. This has several nice diagnostic
pages, accessed at, including logs which give details of any
exceptions and error messages.

Connectivity problems in summer of 2010 were caused by new lines (coax)
from the pole to the box. I was able to prove to the provider that the
intermittant problems were not in my setup, but outside. There were several
issues, which they gradually seemed to fix. One had to do with connectivity
interruptions on the days following a big rainstorm. The connectors in the
new lines (at the pole) had not been weatherproofed, which they did.  Line
techs eventually checked and improved the weatherproofing throughout the
whole neighborhood.

Note that I have no other services (such as TV) which run on the incoming
line. Also note: I have no extra connectors in the coax running between the
box and my modem.

The sick modem I experienced here a few weeks ago may have simply been due
to a failing power supply (wall wart) running the modem.  Somehow that had
never occurred to me. I could have tested that by replacing it with an
equivalent new power supply.

Meanwhile 2 Charter techs had diagnosed my modem as 'dying', shook their
heads when they learned it was 2+ years old, replaced it with one of
theirs, and left. This is a Cisco, which sounded reasonable to me. But
there is only one page available to customers, at and this
only shows that the modem is connected, a few power levels, SNR, how many
channels are running. Further diagnostic pages can be accessed through a
password, but the usual logins and passwords don't work.

My ultimate solution is to get another modem which I will own and have
provisioned when I set it up. The one I'm planning to get is the Motorola
SB 6121, their replacement for the 6120, which they no longer manufacture.

A further note on the SB6120, in case anyone gets one on ebay or whatever:
These are very sensitive to incoming power levels. If the signal is too
"hot", such as 15 dBmV, they start throwing errors. These power levels seem
to vary according to temperature and humidity. Once I installed a 3db
attenuator pad between the incoming coax and my modem,  the power levels
the modem experienced came down to 10 or 12 dBmV, which allowed the modem
to operate without interruption for many months at a time.

I haven't heard if the SB6121 has the same sensitivity to hot power levels
or not. I'm still reading reviews and forum posts about this unit. I can
report on it once I get one in here and running. It will be nice to be able
to see the diagnostics pages and service logs again.

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