NETGEAR is aware of a growing number of phone and online scams. To learn how to stay safe click here.

Forum Discussion

brabq's avatar
brabq
Aspirant
Feb 08, 2021
Solved

CM400: Post-Reset Fast Speeds, then Slow (Downstream Channel Shift?)

I have a CM400 (Netgear) cablemodem, which has worked fine for the last several years. In the last 24 hours, however, I've seen it slow to a crawl. Resetting the cable modem - whether I do it, or Xfi...
  • brabq's avatar
    brabq
    Feb 08, 2021

    For what it's worth, and for anyone that should find this in the future.  Oddly enough, disconnecting the CM400 from power for some time (minutes) before reconnecting it seems to have solved the issue.  Now, the uptime has been >60 minutes and the modem has continued to use the initial/boot downstream channel and has not "chased" the apparently bad-choice downstream channel as it previously had.  I hope this helps someone else.

FURRYe38's avatar
FURRYe38
Guru - Experienced User
Feb 08, 2021

Please post a copy and paste of the modems connection status page.
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. 
Be sure to power OFF the modem for 1 minute them back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Modems/m-p/1530376#M12853

brabq's avatar
brabq
Aspirant
Feb 08, 2021

FURRYe38:

 

Thanks.  Here's what the page looks like currently.  I have performed several resets, and - like clockwork - at "uptime" of 13m0s is when it switches downstream channels and the quality drops.

 

<tabindex=-1>Startup Procedure</tabindex=-1>
ProcedureStatusComment
Acquire Downstream Channel663000000 HzLocked
Connectivity StateOkOperational
Boot StateOkOperational
SecurityEnabledBPI+
IP Provisioning ModeHonor MDDhonorMdd(4)
Downstream Bonded Channels
ChannelLock StatusModulationChannel IDFrequencyPowerSNRCorrectablesUnCorrectables
1LockedQAM 25625627000000 Hz4.8 dBmV37.9 dB72104
2LockedQAM 25626633000000 Hz4.7 dBmV38.2 dB442963
3LockedQAM 25627639000000 Hz4.7 dBmV38.2 dB162032
4LockedQAM 25628645000000 Hz4.7 dBmV38.6 dB211299
5LockedQAM 25629651000000 Hz4.3 dBmV38.2 dB292214
6LockedQAM 25642657000000 Hz2.2 dBmV36.3 dB253867
7LockedQAM 25631663000000 Hz4.0 dBmV38.2 dB292102
8LockedQAM 25632669000000 Hz4.0 dBmV38.2 dB583001
Upstream Bonded Channels
ChannelLock StatusUS Channel TypeChannel IDSymbol RateFrequencyPower
1LockedATDMA15120 Ksym/sec16400000 Hz39.0 dBmV
2LockedATDMA25120 Ksym/sec22800000 Hz39.0 dBmV
3LockedATDMA35120 Ksym/sec29200000 Hz39.0 dBmV
4LockedATDMA45120 Ksym/sec35600000 Hz39.0 dBmV
Current System Time: Mon Feb 8 13:37:31 2021
System Up Time: 02:09:57
 
 
  • brabq's avatar
    brabq
    Aspirant
    Feb 08, 2021

    For what it's worth, and for anyone that should find this in the future.  Oddly enough, disconnecting the CM400 from power for some time (minutes) before reconnecting it seems to have solved the issue.  Now, the uptime has been >60 minutes and the modem has continued to use the initial/boot downstream channel and has not "chased" the apparently bad-choice downstream channel as it previously had.  I hope this helps someone else.