Regular Visitor
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6 Messages
MB8600: Low SNR and huge uncorrected errors on specific downstream channels, no splitters
Hi,
I am seeing an issue that looks very similar to one I had years ago on this same Motorola MB8600:
https://forums.xfinity.com/conversations/your-home-network/mb8600-millions-of-uncorrected-errors-low-signal-to-noise-ratio-snr-slow-gigabit/602dae7ac5375f08cdeb752b
In that older thread, bypassing splitters fixed the issue. This time, there are no splitters and no extra coax. The modem is connected with about 12 inches of coax coming directly from outside the house.
Current status after about 20 hours of modem uptime:
- Modem is online and locked, with Network Access allowed.
- Downstream power levels mostly look normal, generally around -2 to 0 dBmV, with the OFDM PLC around -4 dBmV.
- Upstream channels are locked and around 44.0 to 44.5 dBmV.
- The problem is concentrated on specific downstream channels with very poor SNR and huge uncorrected errors.
Worst downstream channels:
555 MHz / Channel ID 19: SNR around 29.7 dB, 23M+ uncorrected
561 MHz / Channel ID 20: SNR 0.0 dB, 164M+ uncorrected
567 MHz / Channel ID 21: SNR around 29.7 dB, 84M+ uncorrected
573 MHz / Channel ID 22: SNR around 31.6 dB, 1.5M+ uncorrected
627 MHz / Channel ID 31: about 1M uncorrected
633 MHz / Channel ID 32: about 1M uncorrected
The event log repeatedly shows CM-STATUS messages for channel IDs 19, 20, 21, 22, 31, and 32, plus repeated MDD message timeout warnings.
I also checked the modem spectrum analyzer. The full-span sweep looks uneven, with noticeable drops/notches. I can provide screenshots of the connection page, event log, and spectrum analyzer.
Given that there are no splitters and essentially no inside coax to bypass, does this point to downstream ingress/noise or a drop/tap/plant issue? Could Xfinity check the drop, fittings, tap, and downstream impairment around those frequencies?
Thanks.
EFum
Regular Visitor
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6 Messages
5 hours ago
Hi @EG , thanks for your help on my last issue. Is there anything else I need to add to this thread to get help from an expert and/or Xfinity employee?
(edited)
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XfinityRay
Official Employee
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3.9K Messages
3 hours ago
Good evening, @EFum! Thank you for taking the time out of your day to reach out to our community. I am glad that the assistance provided here resolved your concern last time. We aim to do that again! I understand you are seeing intermittent service with timeouts and errors sowing up. You see one channel with a poor SNR. You don't have any splitters and the coax run is short. Anything past that would be repaired by a technician visit. You are correct that this can be noise along the line or at the tap or plant.
We do always recommend resetting the modem and to ensure the cable is finger tight at the back of the modem and where it comes out of the wall outlet. If that has been done, we will need to access your account to run some further testing and get a visit set up.
Please send us a direct message with your full name and complete service address to “Xfinity Support”. To do so, click on the direct messaging icon located at the top right of this forums page.
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