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Question B6121 modem going off-line


Junior Member
May 30, 2020
My older, approximately 5 years modem keeps going off line - AT RANDOM.
The provider checked at demark point and stated the " signal is OK ".
I can access the address and do the same and see "it is OK" .
However, when it last failed the "state" was "off line" and no valid data could be retrieved.
When the modem is off line that is to be expected.
Given the above data - besides having aged internal wiring,

what is a life expectancy of B6121 modem?

Next time it happens I plan to run the modem directly from demark point thus eliminating ALL internal wiring.

Is there a way to check the wirelesses connection when the network cable is disconnected ?

PS The modem is connncetd to RJ45 router and when Intertet goes belly-up the router power light goes "yellow" - I assume that is normal failure idaicator.


Golden Member
Jun 12, 2019
These things are pretty resilient. I have 2x sb6190s that have been in operation now for better part of a decade without fail.

As long as your router isn't blocking it, you should be able to go to and see the status of the modem, even when it is down. Check out the uncorrectable errors (ideally <100) and the event logs for any 'T3 time-out' entries. If you see any of these--it's the isp's signal vs your modem going bad imo.


Junior Member
May 30, 2020
This has been going on for few months, unfortunately I just "discovered" how to check it locally and not to rely on what the provide saiz. Of course it "works" when they test it.
( The provebial " the trouble is leaving form here just fine "...
I need to run more tests when it fails next time. BUT if the error is "off line" I do not see any more tests to run, uinless I can access it wirlessly.
Funny - it clears the error log to 1970 ! So even that is of no help.

Is there way to shut down / restart the modem without power down or unplugging the coax? Just to eliminate any mechanical issues.