Contributor
•
21 Messages
T3 SYNC errors and fail to receive ipv6 prefix Motorola MG8702
I am using a high-spec Motorola MG8702 (DOCSIS 3.1) that is certified for Xfinity, Spectrum and Cox. While my speeds are within the 75/10 plan range, my SNR (Signal-to-Noise Ratio) is clearly failing due to the 'Next-Gen' frequency shifts in my node. My logs prove a physical layer failure (T3 Timeouts/Sync Failures).
When the internet is up, it’s fast and highly efficient, including 2.4 and 5Ghz on the cell phone. But it just cannot stay there!
I also have an Obi VOIP phone adapter, the computer and printer hooked up to the gateway.
I tested with everything hooked up, as well as, only the gateway hooked up. I have rebooted several times, I have released/renewed WAN and reset ipv6 defaults. Nothing fixes it. (And yes the coax connections are snug lol)
(Even though the 8702 is dumber than my old SBG6850 that I have used for years (until 3 days ago), you set everything up and it just worked!). If I am supposed to modernize and get a $200-$300 DOCSIS3.1, wi-fi 5 and ipv6 working, then it needs to work.
Any help is greatly appreciated.
Connection is strong when up and running:
64 bytes from 9.9.9.9: icmp_seq=1 ttl=56 time=15.5 ms
64 bytes from 9.9.9.9: icmp_seq=2 ttl=56 time=15.0 ms
64 bytes from 9.9.9.9: icmp_seq=3 ttl=56 time=17.2 ms
64 bytes from 9.9.9.9: icmp_seq=4 ttl=56 time=16.8 ms
64 bytes from 9.9.9.9: icmp_seq=5 ttl=56 time=15.8 ms
64 bytes from 9.9.9.9: icmp_seq=6 ttl=56 time=14.4 ms
DOWNLOAD 83.77 Mbps
UPLOAD 11.91 Mbps
LATENCY 15ms
JITTER 2ms
Network WAN Connection
IPv4 Address [Edited: "Personal Information"]
Time Since Lease D: 02 H: 03 M: 16 S: 17
Lease Expiration Time Tue Apr 7 00:41:52 2026
IPv6 Address Unspecified
MAC Address XXX
WAN Connection Type DHCP
Multiple disconnects every day, resulting in double or triple reboot attempts at once. It can take 30 minutes of if I am lucky, 5 hours before it loses connection. I am on ethernet on the computer by the way. Cell phone I use wi-fi intermittently, which does not affect this problem.
Computer/BIOS time is correct, but 8702 is failing to sync.
High Uncorrected errors.
Summary Sample of Critical Signaling Failures (Multiples of each statement with Frequency Hopping):
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Time Not Established |
|
Critical (3) |
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SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1; |
|
|
20:35:14 |
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Critical (3) |
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UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1; |
||||||||
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Time Not Established |
|
Notice (6) |
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Honoring MDD; IP provisioning mode = IPv6 |
|||||||||
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00:16:15 |
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Notice (6) |
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DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1; |
|||||||||
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00:16:16 |
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Notice (6) |
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DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1; |
|||||||||
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00:16:29 |
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Notice (6) |
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CM-STATUS message sent. Event Type Code: 16; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1; |
|||||||||
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08:24:58 |
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Critical (3) |
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Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1; |
|||||||||
Provisioning Stalls (Notice 6):
Time Not Established; Honoring MDD; IP provisioning mode = IPv6
OFDM Profile Failure (Notice 6):
19:32:26 Sat Apr 4 2026; CM-STATUS message sent. Event Type Code: 16; Chan ID: 194; OFDM/OFDMA Profile ID: 2 3.
Channel 34 has been as bad as -17.8 dB
Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected
1 Locked QAM256 20 495.0 -6.3 42.3 0 0
2 Locked QAM256 1 381.0 -4.9 43.4 0 0
3 Locked QAM256 2 387.0 -5.1 43.3 0 0
4 Locked QAM256 3 393.0 -4.9 43.7 0 0
5 Locked QAM256 4 399.0 -5.0 43.4 0 0
6 Locked QAM256 5 405.0 -4.8 43.6 0 0
7 Locked QAM256 6 411.0 -5.2 43.3 0 0
8 Locked QAM256 7 417.0 -5.1 43.5 0 0
9 Locked QAM256 8 423.0 -5.5 43.2 0 0
10 Locked QAM256 9 429.0 -5.2 43.5 0 0
11 Locked QAM256 10 435.0 -5.6 43.2 0 0
12 Locked QAM256 11 441.0 -5.7 43.1 0 0
13 Locked QAM256 12 447.0 -5.8 43.0 0 0
14 Locked QAM256 13 453.0 -5.4 43.3 0 0
15 Locked QAM256 14 459.0 -5.8 43.0 0 0
16 Locked QAM256 15 465.0 -5.7 43.0 0 0
17 Locked QAM256 16 471.0 -6.0 42.6 0 0
18 Locked QAM256 17 477.0 -5.6 42.9 0 0
19 Locked QAM256 18 483.0 -6.1 42.6 0 0
20 Locked QAM256 19 489.0 -5.9 42.7 0 0
21 Locked QAM256 21 501.0 -6.3 42.5 0 0
22 Locked QAM256 22 507.0 -6.9 42.1 0 0
23 Locked QAM256 23 513.0 -6.9 42.0 0 0
24 Locked QAM256 24 519.0 -7.2 41.6 0 0
25 Locked QAM256 25 525.0 -7.4 41.4 0 0
26 Locked QAM256 26 531.0 -7.2 41.7 0 0
27 Locked QAM256 27 537.0 -7.0 41.9 0 0
28 Locked QAM256 28 543.0 -7.4 41.3 0 0
29 Locked QAM256 29 549.0 -7.5 41.2 0 0
30 Locked QAM256 30 555.0 -7.4 41.4 0 0
31 Locked QAM256 31 561.0 -7.6 41.1 0 0
32 Locked QAM256 32 567.0 -7.5 41.3 0 0
33 Locked OFDM PLC 193 690.0 -9.0 38.5 7371278 0
34 Locked OFDM PLC 194 957.0 -16.9 34.4 2987758 4505853
Upstream Bonded Channels
Channel Lock Status Channel Type Channel ID Symb. Rate (Ksym/sec) Freq. (MHz) Pwr (dBmV)
1 Locked SC-QAM 1 5120 16.4 49.5
2 Locked SC-QAM 2 5120 22.8 49.3
3 Locked SC-QAM 3 5120 29.2 50.8
4 Locked SC-QAM 4 5120 35.6 49.8
EG
Expert
•
117.3K Messages
7 days ago
The upstream power is on the high side, and it may be intermittently fluctuating even higher to out of spec levels. The downstream power is on the low / weak side as well, and the SNRs on the OFDM channels (33 & 34) are low / 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/reconfigured. 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, or animal chews.
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.
Good luck with it !
(edited)
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ComputerJunkie
Contributor
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21 Messages
7 days ago
I really did try to think of what obvious questions I would be before getting asked and I see I missed some. LOL
I do not need to check to see if there are any splitters-I have 0 splitters nor need for one. If there are any bad splitters they are inside the walls or out at the tap, installed by Comcast/Xfinity.
3 to 5 years ago, I stopped a cable guy, outside to ask for a new length of cable, which is less than 15’ long, to set the equipment where it is still sitting today. I have never moved it-it's undamaged. I just checked and the pins are still a nice color-no visible corrosion. I already stated the connections were snug.
Years ago, I had issues with internet and they said it was a squirrel chewed cable outside-I do not know if it was at the building or in the junction box.
Another year I was told the tech was waiting for his boss because the connections were so entangled he did not know what to do. Both those cases fixed internet inside my flat.
The point is, it’s not inside my walls unless some invisible force is at play.
It’s on Xfinity’s end and I need help. I have a systemic frequency drop at 957 MHz (Channels 33 & 34) that 15 feet of copper cannot cause. This is an External Node/Tap failure - not a loose nut. If anything it’s being caused by the rat’s nest at the tap or even something wrong with the firmware being sent to my gateway.
Because I have only ever received an ipv4 address, an not an ipv6 address and still losing connection any time it tries to pull an ipv6 addy, shows a problem. As stated, the connection is strong, when it’s working, but let it try to change channels from noise or whatever, bam! A 2-3 boot process.
And now that I am back at the computer I just checked the gateway event log again:
Log
Time
Priority
Description
21:01:28
Sat Apr 4 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
21:46:22
Sat Apr 4 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
21:50:13
Sat Apr 4 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
02:46:29
Sun Apr 5 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
02:50:19
Sun Apr 5 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
07:16:27
Sun Apr 5 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
12:01:24
Sun Apr 5 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
13:16:24
Sun Apr 5 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
14:16:22
Sun Apr 5 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Notice (6)
Honoring MDD; IP provisioning mode = IPv6
15:46:15
Sun Apr 5 2026
Notice (6)
DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
15:46:16
Sun Apr 5 2026
Notice (6)
DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
15:46:21
Sun Apr 5 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
15:46:30
Sun Apr 5 2026
Notice (6)
CM-STATUS message sent. Event Type Code: 16; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
Update 4/6/2026: I decided I need to hook the Obi back up because I need to call tomorrow if I don't get any answers. Everything is fine, the 2 green lights, the ethernet data light blinks with the 8702 but I keep getting dial tone, make a call, then the beeps and "There is no service to complete your call." And no error codes.
This tells me the coax outside is too jammed up with noise to talk back and forth correctly.
And again, I want to point out, everything was working fine 4-5 days ago when I was still using the SBG6850 along with the Obi. I find it funny when I called in to activate this gateway, I was told all green so enjoy your internet, yet they did not do diagnostics to make sure EVERYTHING, i.e. ipv6, was working.
01:50:24
Mon Apr 6 2026
Critical (3)
UCD invalid or channel unusable;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
01:50:32
Mon Apr 6 2026
Notice (6)
CM-STATUS message sent. Event Type Code: 16; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
02:01:05
Mon Apr 6 2026
Notice (6)
CM-STATUS message sent. Event Type Code: 16; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
02:05:41
Mon Apr 6 2026
Notice (6)
CM-STATUS message sent. Event Type Code: 24; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
02:18:12
Mon Apr 6 2026
Notice (6)
CM-STATUS message sent. Event Type Code: 16; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
02:19:57
Mon Apr 6 2026
Notice (6)
CM-STATUS message sent. Event Type Code: 24; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
02:27:12
Mon Apr 6 2026
Notice (6)
CM-STATUS message sent. Event Type Code: 16; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=XXX;CMTS-MAC=XXX;CM-QOS=1.1;CM-VER=3.1;
(edited)
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ComputerJunkie
Contributor
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21 Messages
6 days ago
I am truly tired of being ghosted and seeing a lot of others on the forum being ghosted.
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EG
Expert
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117.3K Messages
4 days ago
@ComputerJunkie @XfinityBillie
Please circle back here and post any possible solutions for the issue here in these open public forums so that all readers here may benefit from the exchange / info. This is in keeping with the spirit for which these public help forums were originally intended. Thank you.
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