MG8725 Multiple internet dropoffs daily with SYNC Timing Synchronization failure

These issues cropped up shortly after a trench was dug through my yard to replace a cable to a neighbors house down the street about 6 months ago.

Logs sometimes have weird dates. Not sure, though it looks if the time is correct, many issue happen at 7pm

Not sure what OFDM is but corrected number looks out of whack.

Event Log

Time	Priority	Description
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1;
19:00:36 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:39 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6
06:01:29 Thu Jun 1 2023	Notice(6)	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1;
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:37 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:39 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6
15:15:07 Thu Jun 1 2023	Notice(6)	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:35 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:40 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6
21:15:04 Thu Jun 1 2023	Notice(6)	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:33 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:39 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6
03:06:29 Fri Jun 2 2023	Notice(6)	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:34 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:39 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6
12:52:08 Fri Jun 2 2023	Notice(6)	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:34 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:39 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6
20:16:39 Fri Jun 2 2023	Notice(6)	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:33 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:38 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6
05:54:32 Sat Jun 3 2023	Notice(6)	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:36 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:40 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6
16:20:47 Sat Jun 3 2023	Notice(6)	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:35 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:41 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6
02:30:17 Sun Jun 4 2023	Notice(6)	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:29 Web Dec 31 1969	Critical(3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:37 Web Dec 31 1969	Critical(3)	No Ranging Response received - T3 time-out;CM-MAC=00:00:00:00:00:00;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
19:00:42 Web Dec 31 1969	Notice(6)	Honoring MDD; IP provisioning mode = IPv6

Downstream Bonded Channels

Channel	Lock Status	Modulation	Channel ID	Freq. (MHz)	Pwr (dBmV)	SNR (dB)	Corrected	Uncorrected
1	Locked	256 QAM	9	507.0	12.4	43.3	0	0
2	Locked	256 QAM	6	483.0	12.0	42.9	0	0
3	Locked	256 QAM	7	489.0	12.1	43.0	0	0
4	Locked	256 QAM	8	495.0	12.5	43.2	0	0
5	Locked	256 QAM	10	513.0	12.4	43.3	0	0
6	Locked	256 QAM	11	519.0	12.7	43.4	0	0
7	Locked	256 QAM	12	525.0	12.8	43.2	0	0
8	Locked	256 QAM	13	531.0	12.9	43.2	0	0
9	Locked	256 QAM	14	537.0	12.9	43.3	0	0
10	Locked	256 QAM	15	543.0	13.3	43.4	0	0
11	Locked	256 QAM	16	549.0	13.4	43.3	0	0
12	Locked	256 QAM	17	555.0	13.5	43.5	0	0
13	Locked	256 QAM	18	561.0	13.7	43.5	0	0
14	Locked	256 QAM	19	567.0	13.9	43.5	0	0
15	Locked	256 QAM	20	573.0	13.8	43.6	0	0
16	Locked	256 QAM	21	579.0	13.7	43.5	0	0
17	Locked	256 QAM	22	585.0	13.9	43.5	0	0
18	Locked	256 QAM	23	591.0	14.1	43.6	0	0
19	Locked	256 QAM	24	597.0	14.1	43.6	0	0
20	Locked	256 QAM	25	603.0	13.9	43.4	0	0
21	Locked	256 QAM	26	609.0	13.9	43.5	0	0
22	Locked	256 QAM	27	615.0	14.3	43.4	0	0
23	Locked	256 QAM	28	621.0	14.6	43.5	0	0
24	Locked	256 QAM	29	627.0	14.5	43.5	0	0
25	Locked	256 QAM	30	633.0	14.5	43.3	0	0
26	Locked	256 QAM	31	639.0	14.6	43.6	0	0
27	Locked	256 QAM	32	645.0	14.9	43.5	0	0
28	Locked	256 QAM	33	651.0	14.8	43.5	0	0
29	Locked	256 QAM	34	657.0	14.9	43.4	0	0
30	Locked	256 QAM	35	663.0	15.1	43.6	0	0
31	Locked	256 QAM	36	669.0	15.3	43.7	0	0
32	Locked	OFDM	37	690.0	15.9	43.1	7268943	0

Upstream Bonded Channels

Channel	Lock Status	Channel Type	Channel ID	Symb. Rate (Ksym/sec)	Freq. (MHz)	Pwr (dBmV)
1	Locked	SC-QAM	1	5120	35.6	42.0
2	Locked	SC-QAM	2	5120	29.2	41.5
3	Locked	SC-QAM	3	5120	22.8	41.0
4	Locked	SC-QAM	4	5120	16.4	41.8
5	Locked	SC-QAM	5	1280	39.6	42.0

Responses

Oldest First

Selected Oldest First

Accepted Solution

EG

Expert

•

112.2K Messages

2 years ago

This may or may not be the root cause of the problem (YMMV) but it should be addressed regardless.

The downstream power is too high. It may be over-driving the front-end receiver circuit of the modem. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.

Is there a drop amplifier / powered splitter on the coax cable line leading to the modem ? If so, try removing / bypassing it and see. If not, you can try installing a -6 dB attenuator pad such as this one to knock that power level down and see;

https://www.amazon.com/6db-Attenuator-Pad-1-each/dp/B0013L48XA

It won't affect the upstream power level which is within spec. Good luck !

user_3cb19e

Visitor

•

9 Messages

@EG Do you believe -6 will be the one I need or should i get a -1, -3 and -10? Also, after adding, what downstream power levels should I be shooting for?

Thought I remember my tivo's had trouble with too much power when they switched to all digital

2 years ago

EG

Expert

•

112.2K Messages

@user_3cb19e

I'm sorry. I gave you the wrong link. Don't use an overall attenuator pad like that one. You want to use a forward path-only attenuator like this: https://www.amazon.com/FPA6-54-Forward-Attenuator-DOCSIS-Internet/dp/B08KTRC3XZ

It won't affect the upstream power levels which are in spec as I stated. You can get two of them and put them back to back if one is insufficient. So below +7 dB is good. The closer to 0 dB (zero), the better.

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? Please mark an Accepted Answer! tick

2 years ago

Accepted Solution

EG

Expert

•

112.2K Messages

2 years ago

Sure. Try it and see. And remember that I stated this in my first reply: "This may or may not be the root cause of the problem (YMMV) but it should be addressed regardless". Something else could be going on. Good luck !

EG

Expert

•

112.2K Messages

2 years ago

@user_3cb19e

Please redact all of the CM MAC and the CMTS MAC addresses from your error log entries for your privacy. They are considered to be personal information. The posting of personally identifiable information is a violation of their forum guidelines. The forum bot will not allow your post to be seen publically. It flagged your post as "Private".

user_3cb19e

Visitor

•

9 Messages

@EG Thank you. Not sure what I was thinking. Will the bot change the privacy or do I need to repost?

2 years ago

user_3cb19e

Visitor

•

9 Messages

2 years ago

Attenuator on back order, just installed this morning.

Some channels still high. I bought 2 just incase. Should I install the 2nd also?

TIA

Downstream Bonded Channels

Channel	Lock Status	Modulation	Channel ID	Freq. (MHz)	Pwr (dBmV)	SNR (dB)	Corrected	Uncorrected
1	Locked	256 QAM	9	507.0	6.3	43.2	0	0
2	Locked	256 QAM	6	483.0	5.9	42.8	0	0
3	Locked	256 QAM	7	489.0	6.1	42.9	0	0
4	Locked	256 QAM	8	495.0	6.4	43.1	0	0
5	Locked	256 QAM	10	513.0	6.3	43.2	0	0
6	Locked	256 QAM	11	519.0	6.6	43.2	0	0
7	Locked	256 QAM	12	525.0	6.7	43.3	0	0
8	Locked	256 QAM	13	531.0	6.8	43.2	0	0
9	Locked	256 QAM	14	537.0	6.8	43.3	0	0
10	Locked	256 QAM	15	543.0	7.2	43.2	0	0
11	Locked	256 QAM	16	549.0	7.3	43.3	0	0
12	Locked	256 QAM	17	555.0	7.5	43.4	0	0
13	Locked	256 QAM	18	561.0	7.7	43.3	0	0
14	Locked	256 QAM	19	567.0	7.9	43.5	0	0
15	Locked	256 QAM	20	573.0	7.8	43.4	0	0
16	Locked	256 QAM	21	579.0	7.6	43.5	0	0
17	Locked	256 QAM	22	585.0	7.8	43.4	0	0
18	Locked	256 QAM	23	591.0	8.0	43.5	0	0
19	Locked	256 QAM	24	597.0	8.0	43.5	0	0
20	Locked	256 QAM	25	603.0	7.8	43.3	0	0
21	Locked	256 QAM	26	609.0	7.8	43.5	0	0
22	Locked	256 QAM	27	615.0	8.2	43.3	0	0
23	Locked	256 QAM	28	621.0	8.5	43.6	0	0
24	Locked	256 QAM	29	627.0	8.4	43.4	0	0
25	Locked	256 QAM	30	633.0	8.4	43.1	0	0
26	Locked	256 QAM	31	639.0	8.5	43.5	0	0
27	Locked	256 QAM	32	645.0	8.8	43.5	0	0
28	Locked	256 QAM	33	651.0	8.6	43.4	0	0
29	Locked	256 QAM	34	657.0	8.7	43.4	0	0
30	Locked	256 QAM	35	663.0	9.0	43.5	0	0
31	Locked	256 QAM	36	669.0	9.1	43.6	0	0
32	Locked	OFDM	37	690.0	9.7	43.0	3357068	0

user_3cb19e

Visitor

•

9 Messages

2 years ago

@user_3cb19e

Downstream Bonded Channels

Channel	Lock Status	Modulation	Channel ID	Freq. (MHz)	Pwr (dBmV)	SNR (dB)	Corrected	Uncorrected
1	Locked	256 QAM	9	507.0	0.6	43.5	0	0
2	Locked	256 QAM	6	483.0	0.2	43.4	0	0
3	Locked	256 QAM	7	489.0	0.4	43.4	0	0
4	Locked	256 QAM	8	495.0	0.7	43.7	0	0
5	Locked	256 QAM	10	513.0	0.6	43.5	0	0
6	Locked	256 QAM	11	519.0	0.9	43.7	0	0
7	Locked	256 QAM	12	525.0	1.0	43.7	0	0
8	Locked	256 QAM	13	531.0	1.1	43.6	0	0
9	Locked	256 QAM	14	537.0	1.2	43.6	0	0
10	Locked	256 QAM	15	543.0	1.5	43.6	0	0
11	Locked	256 QAM	16	549.0	1.7	43.8	0	0
12	Locked	256 QAM	17	555.0	1.8	43.7	0	0
13	Locked	256 QAM	18	561.0	2.0	43.7	0	0
14	Locked	256 QAM	19	567.0	2.2	43.9	0	0
15	Locked	256 QAM	20	573.0	2.1	43.6	0	0
16	Locked	256 QAM	21	579.0	2.0	43.7	0	0
17	Locked	256 QAM	22	585.0	2.2	43.7	0	0
18	Locked	256 QAM	23	591.0	2.4	43.9	0	0
19	Locked	256 QAM	24	597.0	2.4	43.7	0	0
20	Locked	256 QAM	25	603.0	2.1	43.6	0	0
21	Locked	256 QAM	26	609.0	2.1	43.8	0	0
22	Locked	256 QAM	27	615.0	2.6	43.5	0	0
23	Locked	256 QAM	28	621.0	2.8	43.6	0	0
24	Locked	256 QAM	29	627.0	2.7	43.7	0	0
25	Locked	256 QAM	30	633.0	2.7	43.5	0	0
26	Locked	256 QAM	31	639.0	2.8	43.8	0	0
27	Locked	256 QAM	32	645.0	3.1	43.7	0	0
28	Locked	256 QAM	33	651.0	2.9	43.7	0	0
29	Locked	256 QAM	34	657.0	3.0	43.8	0	0
30	Locked	256 QAM	35	663.0	3.2	43.7	0	0
31	Locked	256 QAM	36	669.0	3.4	43.7	0	0
32	Locked	OFDM	37	690.0	3.9	43.2	1365191	0

Upstream Bonded Channels

Channel	Lock Status	Channel Type	Channel ID	Symb. Rate (Ksym/sec)	Freq. (MHz)	Pwr (dBmV)
1	Locked	SC-QAM	1	5120	35.6	43.8
2	Locked	SC-QAM	2	5120	29.2	43.3
3	Locked	SC-QAM	3	5120	22.8	42.5
4	Locked	SC-QAM	4	5120	16.4	43.0
5	Locked	SC-QAM	5	1280	39.6	43.8

So, still getting disconnects. Added the 2nd 6db attenuator

Hopefully, this will fix the problem.

If not, well back to the drawing board

EG

Expert

•

112.2K Messages

2 years ago

The values are very good now ! Something else is going on. Perhaps there is noise ingress into the line(s) / an upstream channel / return path impairment somewhere.

There are other signal stat values that can't be read by the modem. They are the "Upstream Rx Power" (Upstream Receive Power Level), the "Upstream SNR Ch." (Upstream Signal To Noise Ratio), and the "Upstream ICFR" (In Channel Frequency Response). These are as equally important in diagnosing connectivity issues as are the modem's stats.

I'm going to escalate your issue to the Comcast corporate employees (The Digital Care Team) who are available to these boards. They will be able to poll the CMTS (Cable Modem Termination System) to check for any real-time degradation and / or error reports, see your node / cable plant, and modem health, and see whether or not everything is in the green zone. They can also see a history plot for the modem and poll the CMTS for those upstream receive signal stats.

You should get a reply here in your topic. Good luck !

user_3cb19e

Visitor

•

9 Messages

2 years ago

Thanks for keeping me in mind. Really, this only started happening after they dug the trench through my yard. I believe my part of the neighborhood has a main feed of some sorts right in my yard. That's why they started digging under my driveway and running through my front yard and under the street down to the neighbors. I believe I am right there where everything diverges <shrug>

Ill keep checking my logs and see if it begins resetting again.

Thanks again

user_3cb19e

Visitor

•

9 Messages

2 years ago

Yes, unfortunately I am still getting errors. Pretty much same ones