T

Visitor

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3 Messages

Fri, Apr 16, 2021 10:55 PM

SB6190 Losing downstream locks

I've got an SB6190 that keeps getting into a state of having a bunch of downstream channels not locked (11 or 12). Right after rebooting the modem (and for about 10-15 minutes), here's what the state looks like:


Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Corrected Uncorrectables
1 Locked 256QAM 33 627.00 MHz -7.50 dBmV 37.36 dB 0 0
2 Locked 256QAM 13 495.00 MHz -20.10 dBmV 30.00 dB 334 0
3 Locked 256QAM 14 507.00 MHz -14.70 dBmV 34.35 dB 0 0
4 Locked 256QAM 15 513.00 MHz -13.60 dBmV 34.93 dB 0 0
5 Locked 256QAM 16 519.00 MHz -11.80 dBmV 35.78 dB 0 0
6 Locked 256QAM 17 525.00 MHz -10.20 dBmV 36.39 dB 6 0
7 Locked 256QAM 18 531.00 MHz -8.80 dBmV 36.61 dB 0 0
8 Locked 256QAM 19 543.00 MHz -7.30 dBmV 37.64 dB 0 0
9 Locked 256QAM 20 549.00 MHz -7.30 dBmV 37.36 dB 0 0
10 Locked 256QAM 21 555.00 MHz -7.50 dBmV 37.36 dB 0 0
11 Locked 256QAM 22 561.00 MHz -7.40 dBmV 37.36 dB 0 0
12 Locked 256QAM 23 567.00 MHz -7.40 dBmV 37.36 dB 0 0
13 Locked 256QAM 24 573.00 MHz -7.70 dBmV 37.64 dB 0 0
14 Locked 256QAM 25 579.00 MHz -7.40 dBmV 37.64 dB 0 0
15 Locked 256QAM 26 585.00 MHz -7.60 dBmV 37.36 dB 0 0
16 Locked 256QAM 27 591.00 MHz -7.70 dBmV 37.36 dB 0 0
17 Locked 256QAM 28 597.00 MHz -7.20 dBmV 37.64 dB 0 0
18 Locked 256QAM 29 603.00 MHz -7.70 dBmV 37.36 dB 0 0
19 Locked 256QAM 30 609.00 MHz -7.40 dBmV 37.36 dB 0 0
20 Locked 256QAM 31 615.00 MHz -7.70 dBmV 37.36 dB 0 0
21 Locked 256QAM 32 621.00 MHz -7.70 dBmV 37.64 dB 0 0
22 Locked 256QAM 34 633.00 MHz -8.00 dBmV 36.39 dB 0 0
23 Locked 256QAM 35 639.00 MHz -6.90 dBmV 36.84 dB 7 0
24 Locked 256QAM 36 645.00 MHz -7.50 dBmV 37.36 dB 0 0
25 Locked 256QAM 37 651.00 MHz -7.30 dBmV 36.90 dB 0 0
26 Locked 256QAM 38 657.00 MHz -6.90 dBmV 36.90 dB 0 0
27 Locked 256QAM 39 663.00 MHz -7.50 dBmV 37.30 dB 0 0
28 Locked 256QAM 40 669.00 MHz -6.60 dBmV 36.90 dB 0 0
29 Locked 256QAM 41 675.00 MHz -7.00 dBmV 36.90 dB 0 0
30 Locked 256QAM 42 681.00 MHz -6.80 dBmV 36.90 dB 0 0
31 Locked 256QAM 43 687.00 MHz -6.70 dBmV 37.30 dB 0 0
32 Locked 256QAM 44 693.00 MHz -7.00 dBmV 36.90 dB 0 0
        

Upstream Bonded Channels  
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power  
1 Locked ATDMA 4 5120 kSym/s 35.60 MHz 42.00 dBmV  
2 Locked ATDMA 5 2560 kSym/s 40.40 MHz 39.50 dBmV  
3 Locked ATDMA 3 5120 kSym/s 29.20 MHz 42.00 dBmV  
4 Locked ATDMA 2 5120 kSym/s 22.80 MHz 42.00 dBmV  
5 Locked ATDMA 1 5120 kSym/s 16.40 MHz 42.00 dBmV  

#### Clearly unhappy with anything less than around 500MHz, but that's only 2 channels.  After about 15 minutes, something happens (nothing is in the event log), causing  a major hiccup in connectivity with packets getting dropped), and this is now the status for the modem:

Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Corrected Uncorrectables
1 Locked 256QAM 25 579.00 MHz -7.30 dBmV 37.64 dB 0 0
2 Not Locked ---- 1 423.00 MHz ---- ---- ---- ----
3 Not Locked ---- 2 429.00 MHz ---- ---- ---- ----
4 Not Locked ---- 3 435.00 MHz ---- ---- ---- ----
5 Not Locked ---- 4 441.00 MHz ---- ---- ---- ----
6 Not Locked ---- 5 447.00 MHz ---- ---- ---- ----
7 Not Locked ---- 6 453.00 MHz ---- ---- ---- ----
8 Not Locked ---- 7 459.00 MHz ---- ---- ---- ----
9 Not Locked ---- 8 465.00 MHz ---- ---- ---- ----
10 Not Locked ---- 9 471.00 MHz ---- ---- ---- ----
11 Not Locked ---- 10 477.00 MHz ---- ---- ---- ----
12 Not Locked ---- 11 483.00 MHz ---- ---- ---- ----
13 Not Locked ---- 12 489.00 MHz ---- ---- ---- ----
14 Locked 256QAM 13 495.00 MHz -20.00 dBmV 30.15 dB 0 0
15 Locked 256QAM 14 507.00 MHz -14.60 dBmV 34.48 dB 0 0
16 Locked 256QAM 15 513.00 MHz -13.50 dBmV 35.08 dB 14 0
17 Locked 256QAM 16 519.00 MHz -11.80 dBmV 35.60 dB 0 0
18 Locked 256QAM 17 525.00 MHz -10.20 dBmV 36.61 dB 8 0
19 Locked 256QAM 18 531.00 MHz -8.80 dBmV 36.61 dB 0 0
20 Locked 256QAM 19 543.00 MHz -7.20 dBmV 37.64 dB 0 0
21 Locked 256QAM 20 549.00 MHz -7.20 dBmV 37.64 dB 0 0
22 Locked 256QAM 21 555.00 MHz -7.40 dBmV 37.64 dB 0 0
23 Locked 256QAM 22 561.00 MHz -7.30 dBmV 37.64 dB 0 0
24 Locked 256QAM 23 567.00 MHz -7.40 dBmV 37.36 dB 0 0
25 Locked 256QAM 24 573.00 MHz -7.70 dBmV 37.30 dB 0 0
26 Locked 256QAM 26 585.00 MHz -7.50 dBmV 37.30 dB 0 0
27 Locked 256QAM 27 591.00 MHz -7.70 dBmV 37.30 dB 0 0
28 Locked 256QAM 28 597.00 MHz -7.20 dBmV 37.30 dB 0 0
29 Locked 256QAM 29 603.00 MHz -7.60 dBmV 37.30 dB 0 0
30 Locked 256QAM 30 609.00 MHz -7.40 dBmV 37.30 dB 0 0
31 Locked 256QAM 31 615.00 MHz -7.60 dBmV 37.30 dB 0 0
32 Locked 256QAM 32 621.00 MHz -7.70 dBmV 36.90 dB 0 0
        

Upstream Bonded Channels  
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power  
1 Locked ATDMA 4 5120 kSym/s 35.60 MHz 42.00 dBmV  
2 Locked ATDMA 5 2560 kSym/s 40.40 MHz 39.50 dBmV  
3 Locked ATDMA 3 5120 kSym/s 29.20 MHz 42.00 dBmV  
4 Locked ATDMA 2 5120 kSym/s 22.80 MHz 42.00 dBmV  
5 Locked ATDMA 1 5120 kSym/s 16.40 MHz 42.00 dBmV  


For some reason all of the channels over 621 MHz are dropped, and the modem tries to connect to a bunch of channels < 500 MHz which have poor power.


Any ideas where the problem might be? Modem? XFinity? Cables?

Responses

BruceW

Gold Problem Solver

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22.3K Messages

1 m ago

All the downstream channel power levels are borderline (too low), and the ones below 540 MHz are out of spec. Network connection problems like this are most often due to poor coax connections or damaged coax cable, usually in or near your home.

If you want to troubleshoot this yourself, please see https://forums.xfinity.com/conversations/your-home-network/connection-troubleshooting-tips/602da777c5375f08cdea3db9#mainmainContent. 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/. It's not likely they can fix the problem remotely. If not, 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.

(edited)

Visitor

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3 Messages

Thanks for the information -- I had read that thread but was trying to figure out why the modem dropped 11 channels that had better power levels (> 621MHz) and then tried to reconnect with the lower frequency channels. Any idea why the modem would drop those channels 10-15 minutes after reboot? (seems to happen after every reboot -- you get 33 good locked channels and then after 10-15 minutes, those 11 channels get dropped and replaced with the lower frequency ones).

Visitor

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3 Messages

Ok, first, kudos to XFinity. We called them last night, they did some remote check, and dispatched a tech today. Using some pretty cool technology graphing things out, they saw a complete dropout in the lower frequencies, found a filter installed at the cable modem (which seemed to fix the specific channel dropping we saw), but the poor lower frequency power was still there.

Tracing it back to the pole, there was a filter installed at the pole as well (apparently because we ordered only internet long long time ago, they installed a filter to only allow the specific frequencies through that the cable modems way back then). After removing that (yes, the bucket truck came out on-demand!), the lower frequencies (< around 520MHz) have gone from -20 to -0.5.  The others have gone from -7ish to -4ish.

BruceW

Gold Problem Solver

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22.3K Messages

Thanks for posting the fix, and good to hear you got it!

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