Community Forum

Random modem reboots - SYNC Timing Synchronization failure

Highlighted
Regular Visitor

Random modem reboots - SYNC Timing Synchronization failure

My NETGEAR C7000v2 modem is randomly restarting throughout the day after 17 months with no issues and I think I've gone through all the troubleshooting I could do by myself. I called support and they said it was the router, but the router support says it's the line.

 

I've swapped in a new cable from the wall to the modem and have a fan running next to it incase of overheating. I have no splitters inside my apartment. Since the error still occurs I have to believe it is the line, but it seems impossible to get a technician out by talking to their call center support. How can I actually get a technician out here to investigate this?

 

TimePriorityDescription
2020-7-27, 01:59:58Notice (6)Honoring MDD; IP provisioning mode = IPv6
2020-7-27, 01:59:43Warning (5)Dynamic Range Window violation
1970-1-1, 00:01:03Notice (6)Honoring MDD; IP provisioning mode = IPv6
1970-1-1, 00:00:43Critical (3)No Ranging Response received - T3 time-out;
1970-1-1, 00:00:40Notice (6)WiFi Interface [wl1] set to Channel 153 (Side-Band Channel:N/A) - Reason:INIT
1970-1-1, 00:00:40Notice (6)WiFi Interface [wl0] set to Channel 11 (Side-Band Channel:N/A) - Reason:INIT
1970-1-1, 00:00:37Critical (3)SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;
2020-7-26, 19:53:57Critical (3)Started Unicast Maintenance Ranging - No Response received - T3 time-out;
1970-1-1, 00:00:46Critical (3)No Ranging Response received - T3 time-out;
1970-1-1, 00:00:39Critical (3)SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;

 

Startup Procedure
ProcedureStatusComment
Acquire Downstream Channel687000000 HzLocked
Connectivity StateOKOperational
Boot StateOKOperational
SecurityEnabledBPI+
IP Provisioning ModeHonor MDDhonorMdd(4)
 
Downstream Bonded Channels
ChannelLock StatusModulationChannel IDFrequencyPowerSNRCorrectablesUncorrectables
1LockedQAM25637687000000 Hz8.4 dBmV39.3 dB10
2LockedQAM25621591000000 Hz9.1 dBmV39.2 dB00
3LockedQAM25622597000000 Hz9.1 dBmV39.2 dB20
4LockedQAM25623603000000 Hz8.9 dBmV38.6 dB00
5LockedQAM25624609000000 Hz8.7 dBmV37.4 dB20
6LockedQAM25625615000000 Hz9 dBmV36.8 dB150
7LockedQAM25626621000000 Hz9.8 dBmV38.4 dB10
8LockedQAM25627627000000 Hz9.9 dBmV38.9 dB340
9LockedQAM25628633000000 Hz10.1 dBmV39.5 dB480
10LockedQAM25629639000000 Hz10.3 dBmV38.9 dB330
11LockedQAM25630645000000 Hz10.2 dBmV39.1 dB250
12LockedQAM25631651000000 Hz10.2 dBmV39.1 dB150
13LockedQAM25632657000000 Hz9.8 dBmV38.8 dB200
14LockedQAM25633663000000 Hz9.9 dBmV38.8 dB100
15LockedQAM25634669000000 Hz9.6 dBmV39.1 dB80
16LockedQAM25635675000000 Hz9.2 dBmV38.4 dB20
17LockedQAM25636681000000 Hz7.9 dBmV39.8 dB00
18LockedQAM25638693000000 Hz8.2 dBmV39.9 dB00
19LockedQAM25639699000000 Hz8.2 dBmV39.6 dB00
20LockedQAM25640705000000 Hz8.4 dBmV39.9 dB00
21LockedQAM25641711000000 Hz9 dBmV40.2 dB00
22LockedQAM25642717000000 Hz9.4 dBmV40 dB00
23LockedQAM25643723000000 Hz9.5 dBmV39.7 dB00
24LockedQAM25644729000000 Hz9.2 dBmV39.9 dB00
 
Upstream Bonded Channels
ChannelLock StatusUS Channel TypeChannel IDSymbol RateFrequencyPower
1LockedATDMA51280 Ksym/sec41200000 Hz51 dBmV
2LockedATDMA15120 Ksym/sec17300000 Hz51 dBmV
3LockedATDMA25120 Ksym/sec23700000 Hz49.5 dBmV
4LockedATDMA35120 Ksym/sec30100000 Hz51 dBmV
5LockedATDMA45120 Ksym/sec36500000 Hz52.5 dBmV
6Not LockedUnknown00 Ksym/sec0 Hz0.0 dBmV
7Not LockedUnknown00 Ksym/sec0 Hz0.0 dBmV
8Not LockedUnknown00 Ksym/sec0 Hz0.0 dBmV
 
Extended Upstream Transmit Power
Enable Extended Upstream Transmit Power
 
Current System Time:Mon Jul 27 02:10:34 2020

System Up Time:00:12:10

Highlighted
Expert

Re: Random modem reboots - SYNC Timing Synchronization failure

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

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.



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!