Regular Visitor
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3 Messages
Degraded download speed, downsteam bonded channel not locked, large uncorrectables
Hello and thank you in advance for any help. I'm a 10+ year Comcast customer; physical exterior wiring untouched since initial customer onboarding. I'm on an up-to 300Mbps plan and until ~2 months ago was receiving consistently >150Mbs over WiFi, which was totally acceptable. No known changes have occurred on my property that would have detrimentally impacted Internet performance. I live at the end of the street = no homes downline of me. Currently, I'm receiving ~35Mpbs maximum wired directly into the cable modem (Arris SB6190). I've activated and provisioned an older second cable modem and the same hardwared download speed performance is observed: ~35Mpbs maximum. On both cable modems tested, there are consistently 3-4 downstream channels either showing Not Locked or some other form of distress, and usually one channel with an overwhelmingly large number of Uncorrectable errors. These 3-4 channels are always grouped together, but do change when the modem is powercycled I've included both my SB6190's Status and Event Log at the bottom.
Objective: determine whether my two cable modems are both defective and require replacement or whether I need a Comcast tech to come out and rehab my wiring/installation. I'd like to remove WiFi entirely from the equation and just focus on speed as measured while hardwired into the cable modem.
As a 10+ year Comcast customer, I am familiar with Xfinity quirks: weekly (or more frequent) cable modem power cycling, call in to have cable modem reprovisioned, etc. I've tried all prior tactics to get my download speeds back up to an approximation of what I'm paying for, to no avail.
I've chatted with Comcast support twice, we do the same standard reboot process, the agent confirms she can proceed no further, and then I'm supposed to receive a call from Advanced Support, which is never received.
Whether coincident or causal remains unknown: my ex-AT&T customer neighbor two houses up-line became a Comcast customer, enjoys glorious >600Mbps over WiFi, having a model experience. This customer's Xfinity activation approximately aligns with my observed download speed performance decline.
My SB6190's Status - currently Channels 10, 11, and 12 show distress - the specific channels in distress change when I powercycle, but 3-4 adjacent channels consistently show problems:
| Channel | Lock Status | Modulation | Channel ID | Frequency | Power | SNR | Corrected | Uncorrectables |
| 1 | Locked | 256QAM | 21 | 555.00 MHz | -1.80 dBmV | 37.36 dB | 0 | 0 |
| 2 | Locked | 256QAM | 13 | 495.00 MHz | -1.10 dBmV | 37.64 dB | 0 | 0 |
| 3 | Locked | 256QAM | 14 | 507.00 MHz | -1.00 dBmV | 37.64 dB | 0 | 0 |
| 4 | Locked | 256QAM | 15 | 513.00 MHz | -1.30 dBmV | 37.36 dB | 11 | 0 |
| 5 | Locked | 256QAM | 16 | 519.00 MHz | -1.30 dBmV | 36.61 dB | 13 | 0 |
| 6 | Locked | 256QAM | 17 | 525.00 MHz | -1.20 dBmV | 36.61 dB | 12 | 0 |
| 7 | Locked | 256QAM | 18 | 531.00 MHz | -1.40 dBmV | 34.48 dB | 5 | 0 |
| 8 | Locked | 256QAM | 19 | 537.00 MHz | -1.30 dBmV | 35.60 dB | 20 | 0 |
| 9 | Locked | 256QAM | 20 | 543.00 MHz | -1.40 dBmV | 34.93 dB | 2 | 0 |
| 10 | Locked | 256QAM | 22 | 561.00 MHz | -1.70 dBmV | 31.69 dB | 17316 | 1613 |
| 11 | Not Locked | ---- | 23 | 567.00 MHz | ---- | ---- | ---- | ---- |
| 12 | Locked | 256QAM | 24 | 573.00 MHz | -1.70 dBmV | 27.64 dB | 194223 | 275612 |
| 13 | Locked | 256QAM | 25 | 579.00 MHz | -1.90 dBmV | 34.93 dB | 99 | 0 |
| 14 | Locked | 256QAM | 26 | 585.00 MHz | -2.10 dBmV | 37.36 dB | 0 | 0 |
| 15 | Locked | 256QAM | 27 | 591.00 MHz | -1.90 dBmV | 37.36 dB | 0 | 0 |
| 16 | Locked | 256QAM | 28 | 597.00 MHz | -1.90 dBmV | 37.36 dB | 0 | 0 |
| 17 | Locked | 256QAM | 29 | 603.00 MHz | -1.80 dBmV | 37.64 dB | 0 | 0 |
| 18 | Locked | 256QAM | 30 | 609.00 MHz | -1.90 dBmV | 37.36 dB | 0 | 0 |
| 19 | Locked | 256QAM | 31 | 615.00 MHz | -2.20 dBmV | 37.36 dB | 0 | 0 |
| 20 | Locked | 256QAM | 32 | 621.00 MHz | -2.10 dBmV | 37.36 dB | 0 | 0 |
| 21 | Locked | 256QAM | 33 | 627.00 MHz | -2.30 dBmV | 36.61 dB | 2 | 0 |
| 22 | Locked | 256QAM | 34 | 633.00 MHz | -2.30 dBmV | 37.36 dB | 0 | 0 |
| 23 | Locked | 256QAM | 35 | 639.00 MHz | -2.20 dBmV | 36.61 dB | 0 | 0 |
| 24 | Locked | 256QAM | 36 | 645.00 MHz | -2.40 dBmV | 36.61 dB | 0 | 0 |
| 25 | Locked | 256QAM | 37 | 651.00 MHz | -2.60 dBmV | 36.90 dB | 0 | 0 |
| 26 | Locked | 256QAM | 38 | 657.00 MHz | -2.30 dBmV | 36.90 dB | 0 | 0 |
| 27 | Locked | 256QAM | 39 | 663.00 MHz | -2.60 dBmV | 36.60 dB | 0 | 0 |
| 28 | Locked | 256QAM | 40 | 669.00 MHz | -2.60 dBmV | 36.60 dB | 0 | 0 |
| 29 | Locked | 256QAM | 41 | 675.00 MHz | -2.20 dBmV | 36.90 dB | 0 | 0 |
| 30 | Locked | 256QAM | 42 | 681.00 MHz | -2.50 dBmV | 36.60 dB | 0 | 0 |
| 31 | Locked | 256QAM | 43 | 687.00 MHz | -2.40 dBmV | 36.60 dB | 0 | 0 |
| 32 | Locked | 256QAM | 44 | 693.00 MHz | -2.30 dBmV | 36.40 dB | 6 | 0 |
| Channel | Lock Status | US Channel Type | Channel ID | Symbol Rate | Frequency | Power |
| 1 | Locked | ATDMA | 6 | 5120 kSym/s | 29.20 MHz | 52.50 dBmV |
| 2 | Locked | ATDMA | 8 | 5120 kSym/s | 16.40 MHz | 54.00 dBmV |
| 3 | Locked | ATDMA | 7 | 5120 kSym/s | 22.80 MHz | 52.50 dBmV |
| 4 | Locked | ATDMA | 5 | 5120 kSym/s | 35.60 MHz | 52.50 dBmV |
Current System Time: Mon Sep 21 09:17:17 2020
The Event Log is an infinite stream of this:
The table below contains the log of events that the SB6190 has detected. This log can be important to the service provider to help diagnose and correct problems, if any should occur.
| Mon Sep 21 09:17:06 2020 | 5 | Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
| Mon Sep 21 09:17:08 2020 | 5 | RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
| Mon Sep 21 09:17:14 2020 | 5 | Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
| Mon Sep 21 09:17:14 2020 | 5 | RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
| Mon Sep 21 09:17:26 2020 | 5 | Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
| Mon Sep 21 09:17:26 2020 | 5 | RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
| Mon Sep 21 09:17:34 2020 | 5 | Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
| Mon Sep 21 09:17:34 2020 | 5 | RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
| Mon Sep 21 09:17:36 2020 | 5 | Lost MDD Timeout;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
| Mon Sep 21 09:17:37 2020 | 5 | RCS Partial Service;CM-MAC=d4:04:cd:24:f5:d1;CMTS-MAC=cc:46:d6:a7:9a:3d;CM-QOS=1.1;CM-VER=3.0; |
Thank you in advance for any help/guidance offered.
BruceW
Gold Problem Solver
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26.5K Messages
5 years ago
Besides the several downstream channels you mentioned, all four upstream channels are out of spec/too high.
If you want to troubleshoot this yourself, please see Internet Troubleshooting Tips. If you can't find the problem or you'd rather have Comcast take care of it, call them at the phone number on your bill or 1-800-Comcast, or use one of the options on https://www.xfinity.com/support/contact-us/. If they can't fix the problem remotely (unlikely), insist they send a tech out to identify the cause and correct it.
If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit unless you have their Service Protection Plan (https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast rental device, or anything outside your home, you shouldn't be charged.
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JB27
Regular Visitor
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3 Messages
5 years ago
Thank you very much @BruceW ! I appreciate your time and assistance - will update on resolution.
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JB27
Regular Visitor
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3 Messages
5 years ago
Updating and closing out this thread: on @BruceW 's recommendation, I requested Comcast send a technician to review overall installation status. Tech arrived yesterday afternoon, assessed all exterior lines/connectors, and tested signal health at each junction.
Observations/actions:
Cable from exterior attic entry to the cable modem is perhaps 130', with at least one known splitter. To address in-attic signal noise would require in-attic inspection, splitter replacement, possible cable replacement, etc. We decided not to do that at this time.
Upon fitting the exterior cabling with modern-style connectors and removing the signal booster (which was itself determined to have little benefit/detriment in our testing), now receiving strong performance inside the house at the cable modem.
Outcome: All errors originally listed above and four downstream channels in distress have been resolved, all 32 downstream channels are now Locked, 0 Uncorrectable errors on all downstream channels, and download and upload speeds are in line with or exceed my plan (>300Mbps down, >20Mbps up). All four upstream bonded channels are at 48.25 dBmV.
The technician advised/reminded me that the signal noise in the attic cabling remains, which may contribute to variable download speeds. We'll address this subsequently if it presents as an issue.
Many thanks!
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BruceW
Gold Problem Solver
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26.5K Messages
5 years ago
That's awfully close to the upper limit, but should be OK if it's stable. Here's hoping it holds for you!
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CCMorgan
Gold Problem Solver
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3.3K Messages
5 years ago
Thank you for reporting back! Take care.
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