We're experiencing frequent upstream signal issues with my Netgear cable modem on Xfinity Gig. The event log consistently shows:
- UCD Invalid or Channel Unusable – Modem struggles to lock on an upstream channel.
- SYNC Timing Synchronization Failures – Indicates loss of sync with the CMTS.
- T3 Timeouts (No Ranging Response Received) – Modem sends ranging requests but doesn't get a response.
- docsDevResetNow Modem Resets – Suggests possible firmware/configuration pushes from Comcast.
Current Modem Stats
- Upstream Power: ~45-46 dBmV (borderline high)
- SNR (Downstream): ~41-44 dB (seems fine)
- OFDM Channels: Locked, but experiencing correctable errors
Troubleshooting Done:
✔ Checked and tightened all coax connections
✔ One splitter as originally installed by Comcast
✔ Manual reboot and full factory reset
✔ Modem is directly connected to the wall jack
This has been consistent for months and last technician who came out did not have any additional advice to resolve.
We're experiencing periodic drops, latency and, at times, packet loss. Could this be an upstream SNR issue or provisioning error on Comcast’s end? Xfinity made a recent change in "CSG" to remove an error they had (originally had the modem listed as CM400 (DOCSIS 3.0) and not CM2000 (DOCSIS 3.1) which we have been using for years (activated and provisioned only with Comcast in the same location).
Any advice or suggestions for additional troubleshooting? Thank you!
| Cable Diagnostic |
| Status: Good |
|
| CM Status: |
|
|
|
|
|
|
|
| Startup Procedure |
| Procedure |
Status |
Comment |
| Acquire Downstream Channel |
399000000 Hz |
Locked |
| Connectivity State |
OK |
Operational |
| Boot State |
OK |
Operational |
| Security |
Enabled |
BPI+ |
| IP Provisioning Mode |
Honor MDD |
IPv6 only |
|
|
|
| Downstream Bonded Channels |
| Channel |
Lock Status |
Modulation |
Channel ID |
Frequency |
Power |
SNR |
Correctables |
Uncorrectables |
| 1 |
Locked |
QAM256 |
4 |
399000000 Hz |
2.0 dBmV |
43.7 dB |
0 |
0 |
| 2 |
Locked |
QAM256 |
1 |
381000000 Hz |
2.1 dBmV |
43.8 dB |
0 |
0 |
| 3 |
Locked |
QAM256 |
2 |
387000000 Hz |
2.0 dBmV |
43.8 dB |
0 |
0 |
| 4 |
Locked |
QAM256 |
3 |
393000000 Hz |
2.0 dBmV |
43.7 dB |
0 |
0 |
| 5 |
Locked |
QAM256 |
5 |
405000000 Hz |
1.9 dBmV |
43.7 dB |
0 |
0 |
| 6 |
Locked |
QAM256 |
6 |
411000000 Hz |
1.7 dBmV |
43.2 dB |
0 |
0 |
| 7 |
Locked |
QAM256 |
7 |
417000000 Hz |
1.8 dBmV |
43.6 dB |
0 |
0 |
| 8 |
Locked |
QAM256 |
8 |
423000000 Hz |
1.6 dBmV |
43.5 dB |
0 |
0 |
| 9 |
Locked |
QAM256 |
9 |
429000000 Hz |
1.7 dBmV |
43.5 dB |
0 |
0 |
| 10 |
Locked |
QAM256 |
10 |
435000000 Hz |
1.9 dBmV |
43.6 dB |
0 |
0 |
| 11 |
Locked |
QAM256 |
11 |
441000000 Hz |
1.8 dBmV |
43.5 dB |
0 |
0 |
| 12 |
Locked |
QAM256 |
12 |
447000000 Hz |
1.9 dBmV |
43.5 dB |
0 |
0 |
| 13 |
Locked |
QAM256 |
13 |
453000000 Hz |
2.0 dBmV |
43.5 dB |
0 |
0 |
| 14 |
Locked |
QAM256 |
14 |
459000000 Hz |
1.7 dBmV |
43.3 dB |
0 |
0 |
| 15 |
Locked |
QAM256 |
15 |
465000000 Hz |
2.0 dBmV |
43.4 dB |
0 |
0 |
| 16 |
Locked |
QAM256 |
16 |
471000000 Hz |
2.0 dBmV |
43.4 dB |
0 |
0 |
| 17 |
Locked |
QAM256 |
17 |
477000000 Hz |
1.8 dBmV |
43.3 dB |
0 |
0 |
| 18 |
Locked |
QAM256 |
18 |
483000000 Hz |
1.8 dBmV |
43.3 dB |
0 |
0 |
| 19 |
Locked |
QAM256 |
19 |
489000000 Hz |
1.9 dBmV |
43.2 dB |
0 |
0 |
| 20 |
Locked |
QAM256 |
20 |
495000000 Hz |
1.8 dBmV |
43.2 dB |
0 |
0 |
| 21 |
Locked |
QAM256 |
21 |
501000000 Hz |
1.8 dBmV |
43.1 dB |
0 |
0 |
| 22 |
Locked |
QAM256 |
22 |
507000000 Hz |
2.0 dBmV |
43.2 dB |
0 |
0 |
| 23 |
Locked |
QAM256 |
23 |
513000000 Hz |
1.6 dBmV |
43.0 dB |
0 |
0 |
| 24 |
Locked |
QAM256 |
24 |
519000000 Hz |
1.8 dBmV |
43.1 dB |
0 |
0 |
| 25 |
Locked |
QAM256 |
25 |
525000000 Hz |
1.6 dBmV |
42.9 dB |
0 |
0 |
| 26 |
Locked |
QAM256 |
26 |
531000000 Hz |
1.2 dBmV |
42.7 dB |
0 |
0 |
| 27 |
Locked |
QAM256 |
27 |
537000000 Hz |
1.4 dBmV |
42.8 dB |
0 |
0 |
| 28 |
Locked |
QAM256 |
28 |
543000000 Hz |
1.3 dBmV |
42.7 dB |
0 |
0 |
| 29 |
Locked |
QAM256 |
29 |
549000000 Hz |
1.2 dBmV |
42.6 dB |
0 |
0 |
| 30 |
Locked |
QAM256 |
30 |
555000000 Hz |
1.4 dBmV |
42.5 dB |
0 |
0 |
| 31 |
Locked |
QAM256 |
31 |
561000000 Hz |
1.3 dBmV |
42.5 dB |
0 |
0 |
| 32 |
Locked |
QAM256 |
32 |
567000000 Hz |
1.2 dBmV |
42.4 dB |
0 |
0 |
|
|
|
| Upstream Bonded Channels |
| Channel |
Lock Status |
US Channel Type |
Channel ID |
Symbol Rate |
Frequency |
Power |
| 1 |
Locked |
ATDMA |
3 |
5120 Ksym/sec |
29200000 Hz |
46.0 dBmV |
| 2 |
Locked |
ATDMA |
2 |
5120 Ksym/sec |
22800000 Hz |
45.8 dBmV |
| 3 |
Locked |
ATDMA |
1 |
5120 Ksym/sec |
16400000 Hz |
45.0 dBmV |
| 4 |
Locked |
ATDMA |
4 |
5120 Ksym/sec |
35600000 Hz |
46.0 dBmV |
| 5 |
Not Locked |
Unknown |
0 |
0 |
0 |
0.0 dBmV |
| 6 |
Not Locked |
Unknown |
0 |
0 |
0 |
0.0 dBmV |
| 7 |
Not Locked |
Unknown |
0 |
0 |
0 |
0.0 dBmV |
| 8 |
Not Locked |
Unknown |
0 |
0 |
0 |
0.0 dBmV |
|
|
|
| Downstream OFDM Channels |
| Channel |
Lock Status |
Profile ID |
Channel ID |
Frequency |
Power |
SNR / MER |
Active Subcarrier
Number Range |
Unerrored
Codewords |
Correctable
Codewords |
Uncorrectable
Codewords |
| 1 |
Locked |
0 ,1 ,2 ,3 |
193 |
722000000 Hz |
3.48 dBmV |
41.5 dB |
388 ~ 3707 |
19058078 |
17381550 |
0 |
| 2 |
Locked |
0 ,1 ,2 ,3 |
194 |
957000000 Hz |
2.68 dBmV |
40.3 dB |
148 ~ 3947 |
19268384 |
17351838 |
0 |
|
|
|
| Upstream OFDMA Channels |
| Channel |
Lock Status |
Modulation / Profile ID |
Channel ID |
Frequency |
Power |
| 1 |
Not Locked |
0 |
0 |
0 Hz |
0 dBmV |
| 2 |
Not Locked |
0 |
0 |
0 Hz |
0 dBmV |
|
|
|
Extended Upstream Transmit Power 
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No Responses!