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Forum Discussion
Reliable cm1200 suddenly dropping on Comcast
I bought this modem a few years ago and it's been rock solid until the past week. I started noticing waiting icons as the internet seemed to have issues. In the early morning hours I get notices that it's offline. After a power cycle it comes back fine for a while. Mostly, it's been dropping for a few minutes and comes back. The early morning drops are a new phenomenon.
For Comcast, I've checked and my firmware seems to be current as v10.11.02. My hardware version is 1.01.
I have no issues with cable tv which makes me think it's not a Comcast issue. But could my data signal be a new issue? I don't know enough to speak intelligently with Comcast about it.
I'm pasting the most recent log. I'm also attaching a pdf of my modem status.
Sun Nov 30 15:38:27 2025 | Critical (3) | No Ranging Response received - T3 time-out; CM-MAC=9c:c9:eb:3f:a4:d8;CMTS-MAC=00:90:f0:4d:00:00; CM-QOS=1.1; CM-VER=3.1; |
Sun Nov 30 15:37:58 2025 | Warning (5) | TCS Partial Service; CM-MAC=9c:c9:eb:3f:a4:d8; CMTS-MAC=00:90:f0:4d:00:00; CM-QOS=1.1;CM-VER=3.1; |
Sun Nov 30 15:37:58 2025 | Critical (3) | UCD invalid or channel unusable;CM-MAC=9c:c9:eb:3f:a4:d8;CMTS-MAC=00:90:f0:4d:00:00;CM-QOS=1.1;CM-VER=3.1; |
3 Replies
Cable connections looks good for the modem.
Any Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem.
Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box.
Be sure your using good quality RG6 coax cable up to the modem.
Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
Be sure to power OFF the modem for 1 minute then back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Modems/m-p/1530376#M12853https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
https://highspeed.tips/docsis-events/
What brand and model# external wifi router is connected to the modem?Thank you. I wanted to add more info in my post but couldn't find a way to edit it.
Waking up early, I found the modem died six hours earlier. Wanting to get more relevant logs I could not load 192.168.100.1 despite the modem running. That seems to be a clue. So unable to access logs for that time period.
The only splitter between my modem and comcast is the original one installed at the DMARC. No other splitter to the modem. As noted no changes to its supply cable to the modem.
From the modem, it's driving an Ubiquiti Edgerouter.
Reviewing the links now, thx.
Have the ISP take a look at the event logs. Something is happening there.
Might ask the ISP for a loaner modem or check into another modem of your own to see if issues continue or not. Hoping the CM1200 hasn't died all the way.
