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SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

New Poster

SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

SB6120 Modem: Seems to shut itself off at random then turn itself back on again. It's happened about 12 times or so in the last 3 to 4 hours. I had this happen before, and had a tech come out and go through the splitters with me and eventually we decided to eliminate all the splitters we could and leave only the ones that were needed. That was 4 years ago when I bought the house. Since then everything has been fine, no issues. I have not added any splitters/added any boxes/ added any tv's... I've not really added or done anything, its the same internet and the same computer, and the same box, its all the same.

 

Yesterday it happened again and today all day. The last 2 hours seem to be the worst. Is there a chance this is something happening outside my junction/box upstream from me somehow? Here are my modem logs.

 

This is the modem log:

Apr 06 2018 20:48:45 5-Warning Z00.0 MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:13 6-Notice N/A Cable Modem Reboot due to IP loss ;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:47:36 3-Critical T05.0 SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:36:33 5-Warning Z00.0 MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:13 6-Notice N/A Cable Modem Reboot due to T4 timeout ;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:35:41 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:35:41 3-Critical R07.0 Unicast Ranging Received Abort Response - initializing MAC;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:35:12 5-Warning Z00.0 MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:13 6-Notice N/A Cable Modem Reboot due to T4 timeout ;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:34:23 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:34:23 3-Critical R07.0 Unicast Ranging Received Abort Response - initializing MAC;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:34:03 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:34:03 3-Critical R07.0 Unicast Ranging Received Abort Response - initializing MAC;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:33:43 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:33:43 3-Critical R07.0 Unicast Ranging Received Abort Response - initializing MAC;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:31:50 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:23:55 5-Warning Z00.0 MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:24 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:13 6-Notice N/A Cable Modem Reboot due to T4 timeout ;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;
Apr 06 2018 20:23:02 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=e4:83:99:5a:4c:b5;CMTS-MAC=00:9e:1e:59:d2:41;CM-QOS=1.1;CM-VER=3.0;

 

Downstream Bonding Channel Value
Channel ID 25  26  27  28 
Frequency 639000000 Hz  645000000 Hz  651000000 Hz  657000000 Hz 
Signal to Noise Ratio 36 dB  36 dB  36 dB  36 dB 
Downstream Modulation QAM256  QAM256  QAM256  QAM256 
Power Level
The Downstream Power Level reading is a snapshot taken at the time this page was requested. Please Reload/Refresh this Page for a new reading
-5 dBmV   -5 dBmV   -5 dBmV   -6 dBmV  

 

Upstream Bonding Channel Value
Channel ID
Frequency 35800000 Hz 
Ranging Service ID 1320 
Symbol Rate 5.120 Msym/sec 
Power Level 52 dBmV 
Upstream Modulation [3] QPSK
[3] 64QAM
 
Ranging Status Success 

 

Signal Stats (Codewords) Bonding Channel Value
Channel ID 25  26  27  28 
Total Unerrored Codewords 14036522  12248464  12248948  12250074 
Total Correctable Codewords 15551  14988  15423  14496 
Total Uncorrectable Codewords 23220  23238  22311  22122 
Expert

Re: SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

The upstream power is borderline too high and may be intermittently fluctuating even higher out of spec. That can cause random disconnects, spontaneous re-booting of the modem, and speed and latency problems.

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there 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 types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

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.


New Poster

Re: SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

Hi EG,

 

The splitters I have now are all installed by a comcast tech who came out 4 years ago. I can have a tech swap them again I guess, but I don't anticipate that would improve the situation. Is there any reason why after 4 years this issue would come back with no changes to equipment or splitters? I currently only have 1 splitter left in between the street and modem, and the tech removed the other 2, and installed this one, 4 yrs ago.

Expert

Re: SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

Coax, connectors and splitters do degrade over time. Most likely your issue is related to wiring in your home, but it could be a problem on Comcast's end or the modem itself could be failing. 

 

Tip: If you need service, sign up for the Service Protection Plan (SPP). It's around $6 a month and you must keep it for at least 60 days after your service call. If you have SPP, you won't incur a service charge. You can sign up when you schedule an appointment.

 

I've asked a Comcast employee to help you. You should expect a reply in this thread. 

Official Employee

Re: SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

Reicaden2, thanks for posting. I don't come across T4 timeouts very often, but when I do, there is usually an issue with the signal on the line toward the plant. Please send me a private message with your full name and account related phone number for help.

New Poster

Re: SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

Private message sent, thanks!

 

I'll document some of it here, in case it helps the next person and to see what others opinions are on how to proceed:

 

I think I identified the problem, but would still need a tech to maybe bring a replacement. I think the Coaxial cable at the street node has degraded/melted. To Identify this: I removed the splitter, and brought my modem outside with an extension cord and connected it directly to the orange drop line from the street that enters my cable box outside. I used a laptop and attached the ethernet to monitor the power levels. SNR seemed fine around 35 to 37 but power levels were at 54 and jumped as high as 57 before the modem rebooted and threw a T4 error. I then went and opened the green "box" on the street and found that the cable to my house was not long enough when initially installed and was attached with a coupler and a smaller piece (1 foot long) of orange coaxial cable to reach the street node post. The smaller 1 foot long piece, has some corrosion on the tip, and the black section of the jacket at the end of the orange sleeve seemed melted. I switched this piece out with a random small piece I had from previous and retested the levels at the junction box. Power levels were 46 and I saw them to go to 48 at one point, but never past 50 that I could tell while standing there monitoring. I then attached it back to my house entry point and checked inside, power levels were the same (there is only 1 splitter so I did not expect a change unless that splitter went bad). Seems stable for the last 24 hours.

 

I would need someone to bring a small piece of outdoor rated coaxial cable to place there though, as the piece I used is for interior use and is the only piece I had available. Since this is something that is outside the home, would I still get charged to have a tech come out and replace that piece?

Expert

Re: SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

Good catch! Anything outside before the ground block is Comcast's problem - no charge to you for repairs. Smiley Happy

New Poster

Re: SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

Thats good to hear! how do i get them to come out and repair it though>? I mean, its working... I just figure an exterior cable would work best.

Expert

Re: SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

@Reicaden2 Send @ComcastKenF a private message. Let him know what you found and ask him to set an appointment up for you. 

Official Employee

Re: SB6120 Modem resets spontaneously- Log says "Cable Modem Reboot due to T4 timeout"

If the outdoor coax piece needs to be replaced, then a tech fee shouldn't apply. 

 

I'll follow up with you in private message. 

 

KenF