MB8611 Downstream Channel Error

The upstream power is too high and it may be intermittently fluctuating even higher to out of spec levels. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding 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.

Hello and thank you for taking the time to reach out to us! I would love to look into this further with you and review the signal levels on our end. Please click on my handle "ComcastBillie" and send us a private message with your full name and address to get started.

Hello,

I am having random disconnect problems with this same modem which I think might be related to EG's post above. Could you share what are "healthy" SNRs and power levels for both upstream and downstream channels? My MB8611 has randomly rebooted 19 times in the last 18 days, and Motorola Technical Support believes it is due to noise on the upstream side as the modem is repeatedly sending ranging requests and receiving no response from the provider. Here are my signal levels:

Downstream Bonded Channels

Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected    1 Locked QAM256 9 507.0 2.2 39.8 0 0    2 Locked QAM256 6 483.0 2.8 40.4 0 0    3 Locked QAM256 7 489.0 2.2 39.8 0 0    4 Locked QAM256 8 495.0 2.1 39.6 0 0    5 Locked QAM256 10 513.0 1.7 39.6 0 0    6 Locked QAM256 11 519.0 2.6 40.2 0 0    7 Locked QAM256 12 525.0 3.4 40.8 0 0    8 Locked QAM256 13 531.0 3.5 40.7 0 0    9 Locked QAM256 14 537.0 3.2 40.5 0 0    10 Locked QAM256 15 543.0 2.2 39.8 0 0    11 Locked QAM256 16 549.0 2.6 40.0 0 0    12 Locked QAM256 17 555.0 2.9 40.3 0 0    13 Locked QAM256 18 561.0 2.2 39.8 0 0    14 Locked QAM256 19 567.0 1.1 39.0 0 0    15 Locked QAM256 20 573.0 1.0 39.0 0 0    16 Locked QAM256 21 579.0 1.6 39.4 0 0    17 Locked QAM256 22 585.0 2.1 39.6 0 0    18 Locked QAM256 23 591.0 2.0 39.5 0 0    19 Locked QAM256 24 597.0 1.9 39.5 0 0    20 Locked QAM256 25 603.0 2.5 40.0 0 0    21 Locked QAM256 26 609.0 3.0 40.2 0 0    22 Locked QAM256 27 615.0 3.6 40.3 0 0    23 Locked QAM256 28 621.0 3.5 40.5 0 0    24 Locked QAM256 29 627.0 2.2 39.7 0 0    25 Locked QAM256 30 633.0 1.6 39.3 0 0    26 Locked QAM256 31 639.0 0.9 39.1 0 0    27 Locked QAM256 32 645.0 1.2 39.4 0 0    28 Locked QAM256 33 651.0 1.4 39.5 0 0    29 Locked QAM256 34 657.0 0.8 39.0 0 0    30 Locked QAM256 35 663.0 0.6 39.1 0 0    31 Locked QAM256 36 669.0 0.8 39.0 0 0    32 Locked OFDM PLC 37 690.0 0.0 37.5 1333930 0

Upstream Bonded Channels

Channel Lock Status Channel Type Channel ID Symb. Rate (Ksym/sec) Freq. (MHz) Pwr (dBmV)    1 Locked SC-QAM 1 5120 35.6 35.3    2 Locked SC-QAM 2 5120 29.2 36.0    3 Locked SC-QAM 3 5120 22.8 35.0    4 Locked SC-QAM 4 5120 16.4 34.5    5 Locked SC-QAM 5 1280 39.6 36.5

And here are the most recent event logs immediately after a disconnect: 

Event Log

Time    Priority    Description      Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     Time Not Established   Notice (6)   Honoring MDD; IP provisioning mode = IPv6     09:33:12 Fri Jun 18 2021   Notice (6)   DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;     09:33:31 Fri Jun 18 2021   Notice (6)   CM-STATUS message sent. Event Type Code: 24; Chan ID: 37; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0.;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;

I have attempted to work with Comcast on this but as is typical of a giant, greedy, monopolistic organization they want to charge me to fix their problem and after filing an FCC complaint against them they finally agreed to send a technician to check the outside wiring for free, did find a problem, supposedly corrected it, and closed the complaint, but still the random disconnects and terrible service continue. 

I am back in contact with them and have let them know I will continue to file more FCC complaints until they actually resolve the issue, but in the interim I would love to better understand how to interpret the upstream and downstream channel signal levels and what a healthy power level and SNR is.