C7000v2 LAN/WLAN Disconnects every ~15 seconds

[cub57000]

Have had this C7000v2 for less than 12 months.

Xfinity ISP

Firmware Version V1.03.08

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TV started losing wifi intermittently yesterday. The TVs network test would succeed then fail, randomly. A couple reboots of the modem/router, same problem. Duplicated with wifi on Android/Windows.

Plugged in Windows via ethernet. Pings look like this:

Pinging 192.168.0.1 with 32 bytes of data
Reply from 192.168.0.1: bytes=32 time<1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time<1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
PING: transmit failed. General failure.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=2ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=2ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
PING: transmit failed. General failure.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.23: Destination host unreachable.
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64
Reply from 192.168.0.1: bytes=32 time=1ms TTL=64

Swapped ethernet cable, no change.

Ability to access web GUI matched up with ability to ping.

Hard reset with pinhole, no change.

Factory reset via the GUI (during 15 seconds of connectivity), no change.

Swapped power supplies, no change.

Called it a night, went and bought an Arris SBG8300, everything immediately/consistently works fine.

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C7000v2 plugged into power only

Ethernet to a Windows PC

Same problem; local connectivity drops every ~15 seconds for about ~15 seconds. Same on all four LAN ports. Same with multiple cables, PCs. Same on Wifi 2.4 and 5.

The only log oddity I can find is the system time appears to be set to the year 1970. There are no messages regarding LAN connectivity that I can find.

Searched around these/other forums and can't seem to find any cases exactly like this. The Netgear is not rebooting, only the LAN is lost.

TL;DR LAN/WLAN connectivity dropping on a steady pattern of ~15 seconds on/off. Reboots, resets, known good cable/device swaps complete. No change.

Any ideas would be appreciated.

-a

[FURRYe38]

Please post a copy and paste of the modems connection status and event log page.
https://kb.netgear.com/30007/How-do-I-obtain-the-cable-connection-information-from-a-NETGEAR-cable-m...
https://kb.netgear.com/30008/How-do-I-view-or-clear-the-event-logs-on-my-NETGEAR-cable-modem-or-mode...

[cub57000]

Thank you for the reply.

Connection status: (there is no coax plugged in, intentionally):

Lan connection

Event log

Time Priority Description
1970-1-1, 00:00:40 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=c8:9e:43:75:23:b8;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
1970-1-1, 00:00:40 Notice (6) WiFi Interface [wl1] set to Channel 153 (Side-Band Channel:N/A) - Reason:INIT
1970-1-1, 00:00:40 Notice (6) WiFi Interface [wl0] set to Channel 11 (Side-Band Channel:N/A) - Reason:INIT
1970-1-1, 00:11:47 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=c8:9e:43:75:23:b8;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
1970-1-1, 00:00:40 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=c8:9e:43:75:23:b8;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
1970-1-1, 00:00:41 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=c8:9e:43:75:23:b8;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
1970-1-1, 00:04:24 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=c8:9e:43:75:23:b8;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;

What the process looks like, cx-wise

[FURRYe38]

Would need to see the requested data with the ISP service coax cable connected.