We recently purchased a new modem (Netgear CM500) which replaced our rented modem (SMCD3GNV). Following a successful activation of the CM500 modem we noticed interruptions in normal internet usage i.e. streaming video was interrupted and websites were unable to connect. I ran a ping test to Google and was receiving "request timed out" every 5-10 seconds. I thought that the modem may have been defective so we went and got another CM500. The new modem successfully activated but also showed the same behavior as the previous CM500. The internet speed tests, ping tests and event logs all provided similar results between the two CM500 modems. In addition to trying the new modem I also double checked the coax connections and swapped out ethernet cables. These are the same connections and cables that were previously being used with no noticeable interruptions etc. Included in this message is connection info, event logs and a ping test following the addition of the new/current modem. All of this information was gathered with the modem connected directly to the PC.
The downstream power is on the weak side and it may be intermittently fluctuating even lower to out of spec levels. That can cause random disconnects, spontaneous re-booting of the modem, speed, and latency problems. And the modem is only locking on to a single upstream channel. There should be 3 or 4. Seems to be a signal impairment problem present. Perhaps there is noise ingress into the line(s) somewhere
Start with this;.
In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there 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 types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test
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 prompt reply EG. I suspected the singular upstream lock indicated an issue. As for the downstream being weak what is an acceptable downstream range? I will check for unneccessary splitters. I am guessing it is best to start from the modem coax and check for splitters towards the drop. We certainly have not added any new splitters. We have had Comcast/Xfinity techs check the line before and they have provided differing assessments i.e. one tech added a booster that plugged in directly beside the modem then the last tech to visit removed that booster. I think we have had noise issues detected before but they resurfaced over time or were never fully resolved. @EG
The closer to 0 dB, the better.