Hello, I'm hoping to get some help with my intermittent connection. I own a MB8600. Quite frequently, I lose connection for a few minutes at a time. I've had this problem for as long as I can remember, but sometimes it is more noticeable than others. Looking at my logs, I've always had difficulty with consecutive T3 timeouts while ranging on upstream channels. In the past, I've used coax splitters to bring down my downstream power levels to the recommended levels, but that seemed to make my connection more unreliable. So now, My modem is connected as directly as possible to the Comcast coaxial line that enters my home. Although it throws out a ton of errors on my modem log, at least my connection is usable for my most important needs (not for online gaming though). I am hoping to be referred to a Comcast technician to evaluate my line quality from their end.
Here are my signals:
The downstream signals look OK, but the upstream levels on channel#4 are out of whack compared to channels #1-3. The levels on all four channels should be about the same. And the error log "Dynamic Range Window" and "Commanded Power Exceeds" errors both suggest a problem in the connection to Comcast's network affecting the upstream channels.
If you want to troubleshoot this yourself, please see Connection Troubleshooting Tips. Problems with Internet service are often due to poor coax connections between your equipment and Comcast's network, usually in or near your home.
If you can't find the problem or you'd rather have Comcast do the troubleshooting, call them at the phone number on your bill or 1-800-Comcast, or or use one of the options on https://www.xfinity.com/support/contact-us/. It isn't likely they can fix this remotely, and if not insist they send a tech out to identify the cause and correct it.
If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit unless you have their Service Protection Plan (https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast rental device, or anything outside your home, you shouldn't be charged.