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SYNC Timing Synchronization Failure and low Downstream Power Levels
Hi there,
My down/up speeds have been extremely sporadic. I pay for 300 down/20 up, and while I sometimes get close to that, I frequently am getting 1-5 Mbps down and 0 - 0.09 Mbps up (basically extremely low). I have an ARRIS Surfboard SB6183 with an TP-Link AC1900 router. I have a service technician coming out tomorrow and would like to avoid having them come out if it's an issue on my end, since I don't want to be charged a service fee.
Here's what I got from my modem dashboard:
| Downstream Bonded Channels | ||||||||
|---|---|---|---|---|---|---|---|---|
| Channel | Lock Status | Modulation | Channel ID | Frequency | Power | SNR | Corrected | Uncorrectables |
| 1 | Locked | QAM256 | 30 | 555000000 Hz | -22.0 dBmV | 29.3 dB | 117927 | 0 |
| 2 | Locked | QAM256 | 31 | 561000000 Hz | -18.8 dBmV | 31.7 dB | 22 | 0 |
| 3 | Locked | QAM256 | 32 | 567000000 Hz | -18.1 dBmV | 31.8 dB | 24 | 0 |
| 4 | Locked | QAM256 | 33 | 573000000 Hz | -18.2 dBmV | 28.0 dB | 6620758 | 735804 |
| 5 | Locked | QAM256 | 34 | 579000000 Hz | -18.4 dBmV | 31.3 dB | 606 | 0 |
| 6 | Locked | QAM256 | 35 | 585000000 Hz | -14.4 dBmV | 33.7 dB | 0 | 0 |
| 7 | Locked | QAM256 | 36 | 591000000 Hz | -12.6 dBmV | 29.8 dB | 15173 | 2 |
| 8 | Locked | QAM256 | 37 | 597000000 Hz | -14.7 dBmV | 32.3 dB | 5 | 0 |
| 9 | Locked | QAM256 | 38 | 603000000 Hz | -19.9 dBmV | 28.8 dB | 5150692 | 85230 |
| 10 | Locked | QAM256 | 39 | 609000000 Hz | -23.3 dBmV | 27.5 dB | 28218909 | 47931 |
| 11 | Locked | QAM256 | 40 | 615000000 Hz | -19.9 dBmV | 30.6 dB | 1842 | 0 |
| 12 | Locked | unknown | 41 | 621000000 Hz | -25.1 dBmV | 0.0 dB | 81772 | 432492 |
| 13 | Locked | unknown | 42 | 627000000 Hz | -22.3 dBmV | 0.0 dB | 208743 | 1106468 |
| 14 | Locked | QAM256 | 43 | 633000000 Hz | -19.0 dBmV | 27.5 dB | 1704896 | 4460497 |
| 15 | Locked | QAM256 | 44 | 639000000 Hz | -20.4 dBmV | 27.1 dB | 2333745 | 4365112 |
| 16 | Locked | QAM256 | 45 | 645000000 Hz | -20.2 dBmV | 29.5 dB | 864100 | 1982090 |
| Upstream Bonded Channels | ||||||
|---|---|---|---|---|---|---|
| Channel | Lock Status | US Channel Type | Channel ID | Symbol Rate | Frequency | Power |
| 1 | Locked | ATDMA | 4 | 5120 Ksym/sec | 35600000 Hz | 54.0 dBmV |
| 2 | Locked | ATDMA | 1 | 5120 Ksym/sec | 16300000 Hz | 54.0 dBmV |
| 3 | Locked | ATDMA | 2 | 5120 Ksym/sec | 22800000 Hz | 54.0 dBmV |
| 4 | Locked | ATDMA | 3 | 5120 Ksym/sec | 29200000 Hz | 54.0 dBmV |
| Time Not Established | Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=redacted;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0; |
Any input would be appreciated.
BruceW
Gold Problem Solver
•
26.5K Messages
1 year ago
Downstream power levels and SNR are out of spec (both too low). The upstream power levels are also out of spec (too high). Network connection problems like this are often due to poor coax connections or damaged coax cable, usually in or near your home. Running the cable through a surge protector, a defective splitter, or too many splitters can cause signal problems as well. If there is an amplifier in the line make sure it's getting power.
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 be sure to keep your service appointment.
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 (approx $100) 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.
Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.
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