Frequent Visitor
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18 Messages
DOCIS 3.1 issues
For about 10 days now, my modem unlocks from DOCIS 3.1 (falls back fine to DOCIS 3.0) and speed is not affected. Looking at the status, all of the channels have signal levels in the -2.9 to -5.4 range except Channel 25 which is the OFDM carrier for 3.1 It is -7.4. It never was that low before. If the signal goes slightly above 7, the DOCIS 3.1 signal locks in. I have a good signal overall, and my cable signal is good according to the X1 tester. Did something change after the system wide maintenance last week?
| Channel ID | Lock Status | Modulation | Frequency | Power | SNR/MER | Corrected | Uncorrectables |
| 13 | Locked | QAM256 | 519000000 Hz | -3.2 dBmV | 43.0 dB | 0 | 0 |
| 1 | Locked | QAM256 | 441000000 Hz | -4.2 dBmV | 42.8 dB | 0 | 0 |
| 2 | Locked | QAM256 | 453000000 Hz | -4.4 dBmV | 42.6 dB | 0 | 0 |
| 3 | Locked | QAM256 | 459000000 Hz | -4.5 dBmV | 42.4 dB | 0 | 0 |
| 4 | Locked | QAM256 | 465000000 Hz | -3.9 dBmV | 42.7 dB | 0 | 0 |
| 5 | Locked | QAM256 | 471000000 Hz | -4.2 dBmV | 42.6 dB | 0 | 0 |
| 6 | Locked | QAM256 | 477000000 Hz | -4.0 dBmV | 42.8 dB | 0 | 0 |
| 7 | Locked | QAM256 | 483000000 Hz | -3.4 dBmV | 43.0 dB | 0 | 0 |
| 8 | Locked | QAM256 | 489000000 Hz | -3.0 dBmV | 43.1 dB | 0 | 0 |
| 9 | Locked | QAM256 | 495000000 Hz | -2.9 dBmV | 43.3 dB | 0 | 0 |
| 10 | Locked | QAM256 | 501000000 Hz | -2.8 dBmV | 43.3 dB | 0 | 0 |
| 11 | Locked | QAM256 | 507000000 Hz | -2.7 dBmV | 43.3 dB | 0 | 0 |
| 12 | Locked | QAM256 | 513000000 Hz | -2.9 dBmV | 43.0 dB | 0 | 0 |
| 14 | Locked | QAM256 | 525000000 Hz | -3.2 dBmV | 43.0 dB | 0 | 0 |
| 15 | Locked | QAM256 | 531000000 Hz | -3.3 dBmV | 42.9 dB | 0 | 0 |
| 16 | Locked | QAM256 | 537000000 Hz | -3.6 dBmV | 42.7 dB | 0 | 0 |
| 17 | Locked | QAM256 | 543000000 Hz | -3.5 dBmV | 42.8 dB | 0 | 0 |
| 18 | Locked | QAM256 | 555000000 Hz | -4.1 dBmV | 42.5 dB | 0 | 0 |
| 19 | Locked | QAM256 | 561000000 Hz | -3.9 dBmV | 42.6 dB | 0 | 0 |
| 20 | Locked | QAM256 | 567000000 Hz | -4.5 dBmV | 42.4 dB | 0 | 0 |
| 21 | Locked | QAM256 | 573000000 Hz | -4.6 dBmV | 42.3 dB | 0 | 0 |
| 22 | Locked | QAM256 | 579000000 Hz | -4.8 dBmV | 42.2 dB | 0 | 0 |
| 23 | Locked | QAM256 | 585000000 Hz | -5.1 dBmV | 41.9 dB | 0 | 0 |
| 24 | Locked | QAM256 | 591000000 Hz | -5.4 dBmV | 41.7 dB | 0 | 0 |
| 25 | Locked | Other | 693000000 Hz | -7.4 dBmV | 37.8 dB | 21269917 | 0 |
| 26 | Not Locked | QAM256 | 0 Hz | 0.0 dBmV | 41.8 dB | 0 | 0 |
| 27 | Locked | QAM256 | 597000000 Hz | -5.4 dBmV | 41.8 dB | 0 | 0 |
| 28 | Locked | QAM256 | 603000000 Hz | -5.2 dBmV | 41.6 dB | 0 | 0 |
| 29 | Locked | QAM256 | 609000000 Hz | -5.5 dBmV | 41.7 dB | 0 | 0 |
| 30 | Locked | QAM256 | 615000000 Hz | -5.6 dBmV | 41.5 dB | 0 | 0 |
| 31 | Locked | QAM256 | 621000000 Hz | -5.8 dBmV | 41.2 dB | 0 | 0 |
| 32 | Locked | QAM256 | 627000000 Hz | -5.9 dBmV | 41.5 dB | 0 | 0 |
Andyr1
Gold Problem Solver
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8K Messages
4 years ago
Your OFDM is locked. That channel below it that says 'not locked' is a bug in the display list. I see that when the OFDM is not the last channel listed on my SB8200.
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EG
Expert
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110.1K Messages
4 years ago
For about 10 days now, my modem unlocks from DOCIS 3.1 (falls back fine to DOCIS 3.0)
How are you determining that ? Do you intermittently see that *Other* channel in the list become Unlocked ? Do you see the front panel *Downstream* / *Receive* indicator light change from blue to green ? Both conditions ?
There is a bit of undesirable *cable tilt* on your line (The higher frequency channels are weaker than the lower frequency ones are). What do the upstream channel power levels look like.
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HankV
Frequent Visitor
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18 Messages
4 years ago
I have an indicator light which changes from blue to green. All green according to Arris means its in DOCIS 3.0 mode. Here are the upstream values. There are no issues with speed, its just that it wont stay in 3.1 mode and it seems to do with signal level. The unlocked is normal. Other means 3.1 OFDM modulation (This all according to Arris). It stays locked without issues until the signal dips to around -7.9 or lower.
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EG
Expert
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110.1K Messages
4 years ago
The upstream power is on the high side and it may be intermittently fluctuating even higher to out of spec levels. And the upper frequency downstream channels are on the weak / low side. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding / un-locking of channels.
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.
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EG
Expert
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110.1K Messages
4 years ago
Quite welcome ! Good luck with it ! Please post back with how things turn out.
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HankV
Frequent Visitor
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18 Messages
4 years ago
Thanks for the info, I've already done everything inside the house that I can. It may be time for someone to come in. Appreciate all the detail in your response and learned a bit especially about the upstream
Hank
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HankV
Frequent Visitor
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18 Messages
4 years ago
I believe I have found the problem. When the house was built, Comcast did not run the cabling into the house from their curb-side demark properly (run outside of their shell instead of inside. As a result the shell cannot be closed. Apparently one of my neighbors who always complains about the boxes being askew must have tried to close it and pinched the wire going into my house. Any idea how I can get Comcast to come back out and fix this issue? See attached photo.
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HankV
Frequent Visitor
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18 Messages
4 years ago
Thanks again!!!
Hank
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EG
Expert
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110.1K Messages
4 years ago
I'm going to escalate your issue to the Comcast corporate employees that are available to these boards. You should get a reply here in your topic. Good luck !
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XfinityThomasC
Official Employee
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2.5K Messages
4 years ago
Hello HankV! First, I’m so glad you chose us as your provider, thank you! 2nd, I’m very sorry for this experience with the DOCSIS 3.1 issues. I'd like to ask you some questions to narrow down the solution to this issue. Can you please send me a PM with your first and last name so I may further assist you? To send a private message, please click my name "ComcastThomasF" then select "Send a Message" on the right side.
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HankV
Frequent Visitor
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18 Messages
4 years ago
I just sent you the info and my email. Hope to hear from you soon. Thanks - Hank
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CTGreybeard
Regular Visitor
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9 Messages
4 years ago
I seem to be having the same problem. My modem is dropping back also. This started happening a couple of weeks ago, first intermittently and now I don't seem to get a DOCSIS 3.1 lock at all.
My upstream seems a little hot (one 49.0, the rest 50.0), all of the downstream channels are locked, noise is in the low 40's except channel 159 at 27.
I was considering a new modem, this is an SB8200, but maybe it's something that can be corrected?
Bill W
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EG
Expert
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110.1K Messages
4 years ago
@CTGreybeard
Please create a new topic of your own here on this board detailing your issue. Thanks.
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