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LSname
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3 Messages

Monday, March 4th, 2024 6:35 PM

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SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing

Hi,

I've been seeing intermittent SYNC logs on my modem for the past 2 months and have also been experiencing random internet drops over the past two months (prior to that its been pretty stable for about a year).  From looking at other questions here, other people occasionally have this issue as well and it requires further investigation on xfinity's end. I can provide logs as well if necessary but I don't see many besides the SYNC errors.

Thanks

Question

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Updated 

1 year ago

386

4

0

EG

Expert

 • 

111.5K Messages

1 year ago

What do the modem's signal stats look like ? 

Please copy all of the text in its entirety of the *Downstream Power Levels*, the *SNR's* (Signal to Noise Ratios), and the *Upstream Power Level* numbers and paste them into your next post.


What is the exact make and model number of the modem / gateway device ?

1

0

LSname

3 Messages

I see bonded channels, ODFM channels and ODFMA channels but nothing about power levels or SNRs.

This is a NETGEAR CM2000.

Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 25 573000000 Hz 0.6 dBmV 41.3 dB 0 0
2 Locked QAM256 1 417000000 Hz 0.3 dBmV 41.2 dB 0 0
3 Locked QAM256 2 423000000 Hz 0.4 dBmV 41.2 dB 0 0
4 Locked QAM256 3 429000000 Hz 0.2 dBmV 41.1 dB 0 0
5 Locked QAM256 4 435000000 Hz 0.1 dBmV 41.1 dB 0 0
6 Locked QAM256 5 441000000 Hz 0.1 dBmV 41.2 dB 0 0
7 Locked QAM256 6 447000000 Hz 0.4 dBmV 41.3 dB 0 0
8 Locked QAM256 7 453000000 Hz 0.5 dBmV 41.4 dB 0 0
9 Locked QAM256 8 459000000 Hz 0.2 dBmV 41.3 dB 0 0
10 Locked QAM256 9 465000000 Hz 0.3 dBmV 41.4 dB 0 0
11 Locked QAM256 10 471000000 Hz 0.4 dBmV 41.4 dB 0 0
12 Locked QAM256 11 477000000 Hz 0.4 dBmV 41.3 dB 0 0
13 Locked QAM256 12 483000000 Hz 0.2 dBmV 41.3 dB 0 0
14 Locked QAM256 13 489000000 Hz 0.2 dBmV 41.3 dB 0 0
15 Locked QAM256 14 495000000 Hz 0.5 dBmV 41.5 dB 0 0
16 Locked QAM256 15 507000000 Hz 0.2 dBmV 40.7 dB 0 0
17 Locked QAM256 16 513000000 Hz 0.1 dBmV 41.3 dB 0 0
18 Locked QAM256 17 519000000 Hz 0.2 dBmV 41.3 dB 0 0
19 Locked QAM256 18 525000000 Hz 0.3 dBmV 41.1 dB 0 0
20 Locked QAM256 19 531000000 Hz 0.0 dBmV 40.9 dB 0 0
21 Locked QAM256 20 543000000 Hz 0.3 dBmV 41.2 dB 0 0
22 Locked QAM256 21 549000000 Hz 0.5 dBmV 41.3 dB 0 0
23 Locked QAM256 22 555000000 Hz 0.3 dBmV 41.2 dB 0 0
24 Locked QAM256 23 561000000 Hz 0.3 dBmV 41.2 dB 0 0
25 Locked QAM256 24 567000000 Hz 0.4 dBmV 41.1 dB 0 0
26 Locked QAM256 26 579000000 Hz 0.5 dBmV 41.3 dB 0 0
27 Locked QAM256 27 585000000 Hz 0.4 dBmV 41.2 dB 0 0
28 Locked QAM256 28 591000000 Hz 0.8 dBmV 41.3 dB 0 0
29 Locked QAM256 29 597000000 Hz 0.9 dBmV 41.4 dB 0 0
30 Locked QAM256 30 603000000 Hz 1.0 dBmV 41.2 dB 0 0
31 Locked QAM256 31 609000000 Hz 0.8 dBmV 41.3 dB 0 0
32 Locked QAM256 32 615000000 Hz 0.6 dBmV 41.3 dB 0 0
 
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 1 2560 Ksym/sec 10400000 Hz 49.0 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 16400000 Hz 49.0 dBmV
3 Locked ATDMA 3 5120 Ksym/sec 22800000 Hz 48.5 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 29200000 Hz 48.5 dBmV
5 Locked ATDMA 5 5120 Ksym/sec 35600000 Hz 47.5 dBmV
6 Locked ATDMA 6 2560 Ksym/sec 40400000 Hz 48.0 dBmV
7 Not Locked Unknown 0 0 0 0.0 dBmV
8 Not Locked Unknown 0 0 0 0.0 dBmV
 
Downstream OFDM Channels
Channel Lock Status Profile ID Channel ID Frequency Power SNR / MER Active Subcarrier
Number Range		 Unerrored
Codewords		 Correctable
Codewords		 Uncorrectable
Codewords
1 Locked 0 ,1 ,2 ,3 159 722000000 Hz 2.98 dBmV 41.3 dB 1126 ~ 2969 281237693 10874045 0
2 Not Locked 0 0 0 Hz 0 dBmV 0 dB 0 ~ 4095 0 0 0
 
Upstream OFDMA Channels
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Not Locked 0 0 0 Hz 0 dBmV
2 Not Locked 0 0 0 Hz 0 dBmV

1 year ago

0

EG

Expert

 • 

111.5K Messages

1 year ago

Yeah. It's all right there. The upstream power is on the high side 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 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/re-configured. 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, etc.

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 !

1

LSname

3 Messages

Perfect, thanks for helping diagnose! I do have a splitter but its installed by xfinity.

We also had some work done back in January to install an EV charger in the vicinity of where the cable comes up and enters the house so I had been thinking there may have been some damage to the cable due to that but wanted to rule out that it was my modem causing issues. I'll check on the cable and probably call out a tech to see if they can help resolve it as well.

Thanks again!

1 year ago

0

EG

Expert

 • 

111.5K Messages

1 year ago

My pleasure ! Good luck with it ! Please post back with how things turn out.

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XfinityEmilyB

Official Employee

 • 

2.1K Messages

1 year ago

@LSname Welcome to our Xfinity Community Forum and thank you @EG for all your expert insight :). Did you get a chance to examine all your wiring? How is your internet connection doing? I'm here to help with troubleshooting and scheduling a technician if needed. 

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