Internet Dropouts with T3 and T4 Timeout Warnings in Modem Log

The upstream power is too high and it may be intermittently fluctuating even farther out of spec. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.

In an effort to try to obtain better connectivity / more wiggle room, check to see if there are any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage from Home Depot, Target, Wal-Mart, etc. Splitters should be swapped with known to be good / new ones to test.

Also check the coax cable for any damage such as cuts, nicks, abrasions, kinks, sharp bends, etc.

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two-way splitter connected directly off of the drop from the street / pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.

Thanks for the reply.  There is only one splitter and comcast supplied it.  As mentioned in original post all connections taken apart and reconnected.  The only support I am receiving is to replace the modem.

@jff6791 

If there is nothing that can be done to improve the connection quality, then you'll need a tech visit as stated. 

Bear in mind that if the premises facing techs can not find or fix a problem at your home, it is they who are responsible for escalating it up to their line / network / maintenance dept. techs. The problem may lie beyond your home in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home. And if the problem is found to be on their side of the demarcation point, there will not be any charge.

Good luck !

Is there any way to arrange one here.  The phone support is implicating the modem.

Yes. I'll escalate this topic to the Comcast corporate employees (The Digital Care Team) who are available to these boards. You should get a reply here in your topic. Good luck !

Thanks.  They did contact me and the soonest appointment for a truck roll was a week+ out.  I did receive a voicemail advising some non specific problem was located and corrected.  The upstream levels are now a little lower but still have uncorrectable errors after rebooting everything:

And there are still critical warnings in log but fewer than before:

Whatever problem was found did not totally address the issue apparently.

@jff6791 

Please redact all of the CM MAC and the CMTS MAC addresses from your error log entries for your privacy. They are considered to be personal information. The posting of personally identifiable information is a violation of their forum guidelines. The forum bot will not allow your post to be seen publically. It flagged your post as "Private". 

The upstream power levels are still N/G. There's no wiggle room.

Apparently there is still an upsteam channel / return path impairment in the line(s) somewhere. This can't be fixed remotely. It takes a *boots on the ground* tech intervention. 

I'll repeat this part: Bear in mind that if the premises facing techs can not find or fix a problem at your home, it is they who are responsible for escalating it up to their line / network / maintenance dept. techs. The problem may lie beyond your home in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home. And if the problem is found to be on their side of the demarcation point, there will not be any charge.

Good luck with it !

Update:  Underground service cable was replaced today (including the overhead splice at pole) but upstream levels only came down 1 or 2 dB.  Another tech was dispatched who traced the issue to line amp supplying the street.  After some adjustments were completed these are the current levels and the log has been clear of entries since:

Glad it got squared away ! Hope things hold up for you ! Best of luck with it !