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Xfinity Gigabit - SYNC Timing Synchronization failure - Speed Issues and Network issues

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Xfinity Gigabit - SYNC Timing Synchronization failure - Speed Issues and Network issues

Hi, 

over the past year or so I am having issues with my Xfinity service. In the meantime I have switched modem 4 times, switched cables from the modem to the computer and also tested with 2 differen t PCs and 1 Macbook Pro (2018). Reset and Factory Reset the modems - had them re-provisioned various times and so on. The modems I currently use is Netgear CM1100 (preferred) or Arris SB8200 (as backup).

 

What happens is that I get Errors in the log files of these modems (same errors on all modems used so far) saying SYNC Timing Synchronization failure. The time of the modem is 1h behind. So local time at the lof below was 17:36:47

 

Here is the latest log:

 

2019-05-09, 16:36:47 Critical (3) SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=3c:37:86:eb:33:c0;CMTS-MAC=00:5f:86:93:80:ee;CM-QOS=1.1;CM-VER=3.1;
2019-05-09, 16:24:44 Warning (5) Dynamic Range Window violation
2019-05-09, 16:24:44 Warning (5) RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=3c:37:86:eb:33:c0;CMTS-MAC=00:5f:86:93:80:ee;CM-QOS=1.1;CM-VER=3.1;
2019-05-09, 16:24:44 Warning (5) Dynamic Range Window violation
2019-05-09, 16:24:44 Warning (5) RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=3c:37:86:eb:33:c0;CMTS-MAC=00:5f:86:93:80:ee;CM-QOS=1.1;CM-VER=3.1;
2019-05-09, 16:24:44 Warning (5) Dynamic Range Window violation
2019-05-09, 16:24:44 Warning (5) RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=3c:37:86:eb:33:c0;CMTS-MAC=00:5f:86:93:80:ee;CM-QOS=1.1;CM-VER=3.1;
Time Not Established Notice (6) Honoring MDD; IP provisioning mode = IPv6
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=3c:37:86:eb:33:c0;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
Time Not Established Critical (3) No Ranging Response received - T3 time-out;CM-MAC=3c:37:86:eb:33:c0;CMTS-MAC=00:5f:86:93:80:ee;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=3c:37:86:eb:33:c0;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

 

As a result of this my line cuts off randomly. The modem resets itself from time to time. Speed fluctuates from 15 Mbps to 450 Mbps (I pay for 1G and Comcast has no solution whatsoever. 

 

Several technicians have been here. Change my line to another one. Maintenance team has been here. Nothing. They don't know why I do not get the speed I should get. It must be all my modems are faulty. Needless to say that I have tested one modem on a friend line and it works fine. 

 

So I was hoping that somebody here might have an idea as to what to do. I have read similar stories on this forum but no solution yet ?

 

Thank you.

 

 

Expert

Re: Xfinity Gigabit - SYNC Timing Synchronization failure - Speed Issues and Network issues

Please also post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.




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Official Employee

Re: Xfinity Gigabit - SYNC Timing Synchronization failure - Speed Issues and Network issues

Hello, sjbhh. Welcome to the Xfinity Forums!

I would like to take a closer look into your signal/health reports to see if we can pinpoint the cause and make repairs so you can enjoy reliable service again.  Please send me a private message with your first and last name so I can assist. 

 

 To send a private message, click my name "ComcastTambrey", then click "send a message".


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Expert

Re: Xfinity Gigabit - SYNC Timing Synchronization failure - Speed Issues and Network issues

@sjbhh 

 

Please post the info that I requested here / publicly as well so as to benefit all readers here. Thank you.



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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!
Official Employee

Re: Xfinity Gigabit - SYNC Timing Synchronization failure - Speed Issues and Network issues

 sjbhh, as I have not heard back from you in some time, I have closed this thread to further comments. I hope you were able to get the help you needed stabilizing your intermittent internet connectivity issue, but if you still need assistance, please feel free to start a new thread.


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Was your question answered? Mark the post as Best Answer!