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Cable Modem problems resolved, I hope

I have been having a problem with my cable modem losing signal strength and then either regaining it, or being unable to establish connection and rebooting automatically for a while now. It has been very frustrating.

I could see errors like these in the Cable Modem’s logs at (most Cable Modems have a local-only web-status page at that address):

Ranging Request Retries exhausted;CM-MAC=b8:16:19:2e:7a:ee;CMTS-MAC=00:01:5c:96:de:64;CM-QOS=1.1;CM-VER=3.0;
Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=b8:16:19:2e:7a:ee;CMTS-MAC=00:01:5c:96:de:64;CM-QOS=1.1;CM-VER=3.0; Cable Modem Reboot due to T4 timeout ;CM-MAC=b8:16:19:2e:7a:ee;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;

When things are working – I’d typically see downstream power levels in the 0 dBmV (-1 or 1, sometimes -2) range across all 8 channels. A few times a week that would drop entirely and the modem would reboot and recover.


Opened and Xfinity Support Chat – was assigned “RAM” who ran through a checklist… mostly more frustrating and boring, except…

one item was to check or replace the coax from wall to cable modem…
when checking it – I discovered a no longer used old T-Splitter inline between – probably from when I had Cable TV as well as Internet only (cancelled that in 2011). An unterminated coax is an antenna if I recall, and that would cause problems.

I removed that from the loop (connected Coax feed directly to the modem , bypassing the old T-Splitter)…

Result: Presto – immediately got 3 dBmV on all 8 channels (much stronger signal) – the un-terminated splitter was the problem I think.

Only time will tell – but I suspect that fixes my issue.

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