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skered
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Tuesday, February 3rd, 2026 1:13 AM

signal issues cable modem

My modem is consistently showing issues isolated to two downstream channels.
Channel ID 42 is accumulating uncorrectable errors rapidly, and Channel ID 43 is accumulating corrected errors at a much higher rate than all other channels.
Every other downstream channel remains clean and stable, and my upstream levels are normal.
I’m connected directly from the wall to the modem, so this isn’t an inside‑wiring issue.
It appears to be a localized impairment affecting only those two channels.
Could you check the line on your side to verify signal quality for those channel IDs?

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EG

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4 hours ago

Are you actually experiencing any connection problems ?

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skered

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12 Messages

Today no.  However, the modem did restart yesterday afternoon that's when I started reading/researching the uncorrectable counts.

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3 hours ago

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skered

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And as of less than 24 hours after that reboot.  Channels 42, 43, and 44 have 3173324, 1074205, and 30530 uncorrected counts.

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3 hours ago

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EG

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3 hours ago

Please copy all of the text in its entirety of the *Downstream Power Levels*, the *SNR's* (Signal to Noise Ratios), and the *Upstream Power Level* numbers, and the correctable and uncorrectable bit errors and paste them into your next post.

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skered

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Downstream Overview
Port ID Frequency (Hz) Modulation Signal strength (dBmV) Signal noise ratio (dB) Octets Correcteds Uncorrectables Channel ID
1 543000000 256QAM 13.400 40.366 2519692890 0 0 28
2 495000000 256QAM 14.100 38.605 2519693035 7 0 20
3 591000000 256QAM 12.800 38.983 2519693155 0 0 36
4 639000000 256QAM 10.900 38.605 2519504728 158215 30533 44
5 453000000 256QAM 13.300 40.366 2519693389 0 0 13
6 459000000 256QAM 13.400 40.946 2519693372 123 0 14
7 465000000 256QAM 13.600 40.366 2519693607 12 0 15
8 471000000 256QAM 13.700 40.946 2519693716 8 0 16
9 477000000 256QAM 13.800 40.366 2519693840 0 0 17
10 483000000 256QAM 14.100 38.983 2519693929 26 0 18
11 489000000 256QAM 13.800 38.983 2519694050 13 0 19
12 501000000 256QAM 13.700 40.366 2519694166 3 0 21
13 507000000 256QAM 14.000 38.605 2519694296 0 0 22
14 513000000 256QAM 14.000 37.356 2519694409 0 0 23
15 519000000 256QAM 13.800 38.605 2519694519 0 0 24
16 525000000 256QAM 13.900 38.983 2519694632 0 0 25
17 531000000 256QAM 13.700 38.983 2519694758 0 0 26
18 537000000 256QAM 13.900 38.983 2519694876 0 0 27
19 549000000 256QAM 13.700 38.983 2519694981 0 0 29
20 555000000 256QAM 13.500 40.366 2519695094 0 0 30
21 561000000 256QAM 13.400 38.605 2519695212 0 0 31
22 567000000 256QAM 13.300 38.983 2519695319 0 0 32
23 573000000 256QAM 13.000 38.983 2519695434 0 0 33
24 579000000 256QAM 13.100 38.983 2519695554 0 0 34
25 585000000 256QAM 12.600 38.983 2519695671 0 0 35
26 597000000 256QAM 12.400 38.983 2519695776 0 0 37
27 603000000 256QAM 12.000 38.983 2519695893 0 0 38
28 609000000 256QAM 11.900 38.983 2519695997 0 0 39
29 615000000 256QAM 11.500 38.605 2519696121 0 0 40
30 621000000 256QAM 11.700 38.983 2519696226 0 0 41
31 627000000 256QAM 11.200 38.605 2511918179 1980778 3181645 42
32 633000000 256QAM 11.400 37.636 2512251807 5808032 1092589 43
Reset FEC Counters
OFDM Downstream Overview
Receiver FFT type Subcarr 0 Frequency(Hz) PLC locked NCP locked MDC1 locked PLC power(dBmv) SNR(dB) Octets Correcteds Uncorrectables
0 4K 623600000 YES YES YES 10.300003 40 338816534 320873943 87
1 4K 803600000 YES YES YES 0.500000 37 678347148 602365208 88
Reset FEC Counters
Upstream Overview
Port ID Frequency (Hz) BandWidth (Hz) Modulation Type DOCSIS Mode Signal Strength (dBmV) Channel ID
1 22800000 6400000 64QAM ATDMA 38.521 18
2 35600000 6400000 64QAM ATDMA 40.021 20
3 29200000 6400000 64QAM ATDMA 38.771 19
4 16400000 6400000 64QAM ATDMA 38.271 17
OFDMA Upstream Overview
Channel Index State Subcarr 0 Frequency(Hz) lin Digital Att Digital Att BW (sc's*fft) Report Power Report Power1_6 FFT Size
0 OPERATE 36200000 0.1724 5.7102 44.4000 52.6826 38.2500 4K
1 DISABLED 0 0.0000 0.0000 0.0000 0.0000 0.0000 2K

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3 hours ago

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EG

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115.8K Messages

3 hours ago

This may or may not be the root cause of the problem (YMMV), but it should be addressed regardless.


The downstream power is too high / out of spec. It may be overdriving the front-end receiver circuit of the modem. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.


Is there a drop amplifier on the coax cable line leading to the modem ? If so, try removing / bypassing it and see. If not, you can try installing a -6 attenuator pad such as this one on the coax port on the rear of the modem to knock that power level down and see;

https://www.amazon.com/6db-Attenuator-Pad-1-each/dp/B0013L48XA 

I don't see any channels 42, 43, or 44 listed there ? 

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EG

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115.8K Messages

2 hours ago

You can go the tech visit route if you so choose. Good luck !

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skered

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1 hour ago

I'd assume Xfinity should be able to do an init. triage here?   Can we get a CC* member to comment here?

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