The CM3000, which I have owned for <30 days, is having repeated disconnection issues. Cox is my ISP. The disconnections occur randomly, but multiple times per day and always require a hard reboot. The Event Log shows many lines associated with each disconnect, but the "critical" error that prompts the disconnect appears to be the following: SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1; This identical entry has occurred dozens of times. Cox technicians have replaced all cable lines and connections to and from the modem out to the street. The last Cox service technician says that the modem is failing to maintain an upstream channel lock and that the problem is with the modem. Additional information:ChannelLock StatusModulationChannel IDFrequencyPowerSNRCorrectablesUncorrectables1LockedQAM2565141000000 Hz7.9 dBmV45.6 dB002LockedQAM2561117000000 Hz7.6 dBmV45.2 dB003LockedQAM2562123000000 Hz7.9 dBmV45.6 dB004LockedQAM2563129000000 Hz7.9 dBmV45.6 dB005LockedQAM2564135000000 Hz8.0 dBmV45.8 dB006LockedQAM2566147000000 Hz7.8 dBmV45.9 dB007LockedQAM2567153000000 Hz7.7 dBmV45.9 dB008LockedQAM2568159000000 Hz7.7 dBmV45.9 dB009LockedQAM2569165000000 Hz7.6 dBmV45.9 dB0010LockedQAM25610171000000 Hz7.6 dBmV46.0 dB0011LockedQAM25611177000000 Hz7.5 dBmV45.9 dB0012LockedQAM25612183000000 Hz7.7 dBmV46.0 dB0013LockedQAM25613189000000 Hz7.7 dBmV46.0 dB0014LockedQAM25614195000000 Hz7.8 dBmV44.5 dB0015LockedQAM25615201000000 Hz7.8 dBmV45.1 dB0016LockedQAM25616207000000 Hz7.8 dBmV45.3 dB0017LockedQAM25617213000000 Hz7.9 dBmV46.0 dB0018LockedQAM25618219000000 Hz7.8 dBmV46.1 dB0019LockedQAM25619225000000 Hz7.7 dBmV46.2 dB0020LockedQAM25620231000000 Hz7.7 dBmV46.3 dB0021LockedQAM25621237000000 Hz7.5 dBmV46.3 dB0022LockedQAM25622243000000 Hz7.5 dBmV46.3 dB0023LockedQAM25623249000000 Hz7.4 dBmV46.3 dB0024LockedQAM25624255000000 Hz7.4 dBmV46.0 dB0025LockedQAM25625735000000 Hz6.0 dBmV44.1 dB0026LockedQAM25626741000000 Hz6.0 dBmV44.0 dB0027LockedQAM25627747000000 Hz5.9 dBmV43.9 dB0028LockedQAM25628753000000 Hz6.2 dBmV43.9 dB0029LockedQAM25629759000000 Hz6.1 dBmV43.8 dB0030LockedQAM25630765000000 Hz6.0 dBmV43.8 dB0031LockedQAM25631771000000 Hz5.9 dBmV43.7 dB0032LockedQAM25632777000000 Hz5.7 dBmV43.6 dB00 Upstream Bonded Channels (Partial Service)ChannelLock StatusUS Channel TypeChannel IDSymbol RateFrequencyPower1LockedATDMA25120 Ksym/sec24000000 Hz34.5 dBmV2LockedATDMA15120 Ksym/sec17600000 Hz34.0 dBmV3LockedATDMA35120 Ksym/sec30400000 Hz34.5 dBmV4LockedATDMA45120 Ksym/sec36800000 Hz35.0 dBmV5Not LockedUnknown0000.0 dBmV6Not LockedUnknown0000.0 dBmV7Not LockedUnknown0000.0 dBmV8Not LockedUnknown0000.0 dBmV Downstream OFDM ChannelsChannelLock StatusProfile IDChannel IDFrequencyPowerSNR / MERActive SubcarrierNumber RangeUnerroredCodewordsCorrectableCodewordsUncorrectableCodewords1Locked0 ,1 ,2 ,3159300000000 Hz7.78 dBmV45.5 dB296 ~ 7895822941641716482102Locked0 ,1 ,2 ,3160918000000 Hz7.18 dBmV43.4 dB2216 ~ 5975821676771106610534 Upstream OFDMA ChannelsChannelLock StatusModulation / Profile IDChannel IDFrequencyPower1Not Locked11 ,13636800000 Hz31.0 dBmV2Not Locked000 Hz0 dBmV Advice, assistance would be much appreciated.

All this is on the ISP. Got word that the ISP has corrected this on there side. CM3000 modems should be good now. Please contact the ISP for continued help and information regarding this. Good Luck.

I am providing the results of my further investigation. This assessment comes from a ChatGPT analysis of the CM3000 diagnostic information and event logs: Observed Technical Symptoms:1. Modem Diagnostic Status: - Startup Procedure: Successfully completes downstream acquisition, DHCP, and provisioning. - Cable Diagnostic: Status = Poor | Mode = Partial Service2. Upstream Bonding (SC-QAM & OFDMA): - Channels 1–4 (ATDMA) locked at: - Frequencies: 17.6–36.8 MHz - Power: 34.0 to 35.0 dBmV - Channel 5 and OFDMA Upstream Channel 1 (Channel ID 6 @ 36.8 MHz): - Not Locked - Power reported = 0 dBmV - Modulation/Profile = 11,13 - Power when it appears = 31.0 dBmV3. Downstream: - All 32 SC-QAM channels locked with SNR from 43.7 to 46.3 dB, power +5.8 to +8.0 dBmV - Two OFDM downstream channels locked, minimal correctables, zero uncorrectables4. DOCSIS Event Log (during each drop): - SYNC Timing Synchronization failure – Failed to acquire QAM/QPSK symbol timing - RNG-RSP CCAP Commanded Power Exceeds Value - Dynamic Range Window violation - DHCP Warning – Non-critical field invalid in response - Unrecognized OID - US profile assignment changeTechnical Assessment:The modem consistently fails to lock Channel 5 or the OFDMA upstream path (~36.8 MHz), which appears to be required under certain provisioning states or load.- OFDMA Channel ID 6 remains in a Not Locked state, often with low reported power (31.0 dBmV), likely below CMTS thresholds or too noisy to maintain sync.- The SYNC Timing and RNG-RSP events suggest return path SNR or ingress noise impairments, likely within the 24–40 MHz range, or an upstream profile mismatch with the CMTS.Advice would be appreciated.

Power is a bit high on some channels. What FW is loaded on the modem? Please post the Event logs data page so we can see that data.

Latest firmware is loaded. Event

Event Log: Fri May 30 14:27:11 2025(Critical (3))No Ranging Response received - T3 time-out;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;Fri May 30 14:25:42 2025(Notice (6))US profile assignment change. US Chan ID: 6; Previous Profile: 13; New Profile: 10 13.;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;Fri May 30 14:25:29 2025(Warning (5))Dynamic Range Window violationFri May 30 14:25:29 2025(Warning (5))RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;Fri May 30 14:25:24 2025(Notice (6))DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;Fri May 30 14:25:22 2025(Notice (6))DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;Fri May 30 14:25:17 2025(Notice (6))TLV-11 - unrecognized OID;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;Time Not Established(Warning (5))DHCP WARNING - Non-critical field invalid in response ;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;Time Not Established(Notice (6))Honoring MDD; IP provisioning mode = IPv4Time Not Established(Critical (3))SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

MojoGene

Tutor

May 29, 2025

CM3000 Repeated Cox disconnects with SYNC Timing Synchronization failure

The CM3000, which I have owned for <30 days, is having repeated disconnection issues. Cox is my ISP. The disconnections occur randomly, but multiple times per day and always require a hard reboot. The Event Log shows many lines associated with each disconnect, but the "critical" error that prompts the disconnect appears to be the following:

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

This identical entry has occurred dozens of times.

Cox technicians have replaced all cable lines and connections to and from the modem out to the street. The last Cox service technician says that the modem is failing to maintain an upstream channel lock and that the problem is with the modem.

Additional information:

Channel	Lock Status	Modulation	Channel ID	Frequency	Power	SNR	Correctables	Uncorrectables
1	Locked	QAM256	5	141000000 Hz	7.9 dBmV	45.6 dB	0	0
2	Locked	QAM256	1	117000000 Hz	7.6 dBmV	45.2 dB	0	0
3	Locked	QAM256	2	123000000 Hz	7.9 dBmV	45.6 dB	0	0
4	Locked	QAM256	3	129000000 Hz	7.9 dBmV	45.6 dB	0	0
5	Locked	QAM256	4	135000000 Hz	8.0 dBmV	45.8 dB	0	0
6	Locked	QAM256	6	147000000 Hz	7.8 dBmV	45.9 dB	0	0
7	Locked	QAM256	7	153000000 Hz	7.7 dBmV	45.9 dB	0	0
8	Locked	QAM256	8	159000000 Hz	7.7 dBmV	45.9 dB	0	0
9	Locked	QAM256	9	165000000 Hz	7.6 dBmV	45.9 dB	0	0
10	Locked	QAM256	10	171000000 Hz	7.6 dBmV	46.0 dB	0	0
11	Locked	QAM256	11	177000000 Hz	7.5 dBmV	45.9 dB	0	0
12	Locked	QAM256	12	183000000 Hz	7.7 dBmV	46.0 dB	0	0
13	Locked	QAM256	13	189000000 Hz	7.7 dBmV	46.0 dB	0	0
14	Locked	QAM256	14	195000000 Hz	7.8 dBmV	44.5 dB	0	0
15	Locked	QAM256	15	201000000 Hz	7.8 dBmV	45.1 dB	0	0
16	Locked	QAM256	16	207000000 Hz	7.8 dBmV	45.3 dB	0	0
17	Locked	QAM256	17	213000000 Hz	7.9 dBmV	46.0 dB	0	0
18	Locked	QAM256	18	219000000 Hz	7.8 dBmV	46.1 dB	0	0
19	Locked	QAM256	19	225000000 Hz	7.7 dBmV	46.2 dB	0	0
20	Locked	QAM256	20	231000000 Hz	7.7 dBmV	46.3 dB	0	0
21	Locked	QAM256	21	237000000 Hz	7.5 dBmV	46.3 dB	0	0
22	Locked	QAM256	22	243000000 Hz	7.5 dBmV	46.3 dB	0	0
23	Locked	QAM256	23	249000000 Hz	7.4 dBmV	46.3 dB	0	0
24	Locked	QAM256	24	255000000 Hz	7.4 dBmV	46.0 dB	0	0
25	Locked	QAM256	25	735000000 Hz	6.0 dBmV	44.1 dB	0	0
26	Locked	QAM256	26	741000000 Hz	6.0 dBmV	44.0 dB	0	0
27	Locked	QAM256	27	747000000 Hz	5.9 dBmV	43.9 dB	0	0
28	Locked	QAM256	28	753000000 Hz	6.2 dBmV	43.9 dB	0	0
29	Locked	QAM256	29	759000000 Hz	6.1 dBmV	43.8 dB	0	0
30	Locked	QAM256	30	765000000 Hz	6.0 dBmV	43.8 dB	0	0
31	Locked	QAM256	31	771000000 Hz	5.9 dBmV	43.7 dB	0	0
32	Locked	QAM256	32	777000000 Hz	5.7 dBmV	43.6 dB	0	0

Upstream Bonded Channels (Partial Service)

Channel	Lock Status	US Channel Type	Channel ID	Symbol Rate	Frequency	Power
1	Locked	ATDMA	2	5120 Ksym/sec	24000000 Hz	34.5 dBmV
2	Locked	ATDMA	1	5120 Ksym/sec	17600000 Hz	34.0 dBmV
3	Locked	ATDMA	3	5120 Ksym/sec	30400000 Hz	34.5 dBmV
4	Locked	ATDMA	4	5120 Ksym/sec	36800000 Hz	35.0 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	159	300000000 Hz	7.78 dBmV	45.5 dB	296 ~ 7895	82294164	17164821	0
2	Locked	0 ,1 ,2 ,3	160	918000000 Hz	7.18 dBmV	43.4 dB	2216 ~ 5975	82167677	11066105	34

Upstream OFDMA Channels

Channel	Lock Status	Modulation / Profile ID	Channel ID	Frequency	Power
1	Not Locked	11 ,13	6	36800000 Hz	31.0 dBmV
2	Not Locked	0	0	0 Hz	0 dBmV

Advice, assistance would be much appreciated.

cm3000

22 Replies

Replies have been turned off for this discussion

BrokenRubber
Aspirant
Aug 24, 2025
Same issue with my modem and cox, had 5 techs on site they replaced everything inside and outside my home, made a FCC complaint with cox they replaced a bunch of stuff on the street as well as the hub and still having the same problems as so many other people (up stream not locking, constant disconnects, intermittent disconnects, and disconnects where nothing show up in the logs and everything shows good connection but have no internet) i really wish i could have returned this modem at this point, i bought it back in may it worked for about 20 days and than the problem's started when they pushed this firmware. and here we all are with a 300$ piece of useless equipment. kind of crazy this has started 3 months ago and netgear hasn't really done anything to fix this.
- FURRYe38
  Guru - Experienced User
  Aug 26, 2025
  All users having the CM3000 modem with v6 FW need to tell the ISP to roll back the FW to prior working FW. Only ISPs can effect this revert in FW. CC/XF has already rolled users back. Make contact with NG support in regards to let them know your situation. NG has already been working with most ISPs regarding this.
  
  Nothing further can be done here in the forums.
  
  Good Luck.
  - FURRYe38
    Guru - Experienced User
    Aug 27, 2025
    All this is on the ISP. Got word that the ISP has corrected this on there side. CM3000 modems should be good now. Please contact the ISP for continued help and information regarding this.
    
    Good Luck.
MojoGene
Tutor
Jun 06, 2025
Thanks. I have the 500G service and typically experience downloads speeds in the 500-600G range with uploads 50-60G range. Plenty for what I do and no hiccups (for now).
- iFrog
  Guide
  Jun 06, 2025
  Gotcha, I had that while I was troubleshooting my connection being unstable on gigabit. Works well, so yeah, the SB8200 will be fine for that if it stays stable. Also the one before that ending in 90, I think 6190 is also certified for 500 with Cox and that's a 3.0 modem. Either way, glad you got it sorted, and you can enjoy a stable connection again.
iFrog
Guide
Jun 06, 2025
Also, because I can't edit my last post to add this, I prefer the S33 as it has the 2.5G port and even with a 1G package, having a 2.5 connection gives you the full Gigi so not capped at 940 Mbps.
MojoGene
Tutor
Jun 01, 2025
Thanks iFrog. I posted on the Reddit page.
- iFrog
  Guide
  Jun 01, 2025
  You're welcome.
MojoGene
Tutor
May 31, 2025
Thanks, iFrog. The first Cox service reps who came out identified a number of issues with the lines, which were probably 30 years old and revealing signal degradation. He replaced every line and connection from the modem out to the street and even some in the local area. The infrastructure is now pristine. Curiously, the upload channel issues appeared only after all the upgrade work was done.

I did notice that on those occasions when the cable modem connection status shows "Good" the diagnostic information shows that Upstream Channel OFDMA #1 is locked. The modem then (apparently) encounters a condition that flips it "Poor" with OFDMA Channel #1 unlocked.
- iFrog
  Guide
  May 31, 2025
  If you take a look at this Reddit thread, it suggests the latest firmware for this modem is partly responsible for the issues:
  https://www.reddit.com/r/NETGEAR/comments/1kxeazx/cm3000_cable_modem_new_firmware_v60103_slow_webui/
MojoGene
Tutor
May 30, 2025
Hardware Version 1.01
- iFrog
  Guide
  May 31, 2025
  Hey, Just reporting the same issues with my CM3000 and Cox. The modem wasn't able to hold a solid connection, even though the lights on both my router and modem suggested otherwise.
  When the Cox tech was out he replaced old connectors in the wall where the modem connects to coaxial, and in the closet where the outside line comes into the apartment.
  
  In my case, I have a direct line from the tap to the wall, no splitters in between, which makes my signal come in a bit high, but is still within spec for Cox. Anyway, the tech gave me, a 6db attenuator for the modem, and when connected, it flips the poor signal, the upstream turns yellow and download turns green. Without the attenuator, my status is the same as the OP, downstream green, and upstream yellow. My firmware, and hardware version(s) are also identical to op's. I drew the conclusion that the Netgear, can't deal with the signal in this particular environment, as I put an Arris S33 into use, with the attenuator, and it holds a perfect connection, and the only issues I've had are known Cox outages.
  
  Historical.y I've had issues with Netgear products except my Gigabit 8 port ProSafe switch, but wanted to try the CM3000 as a troubleshooting measure when I was having issues with the Arris, as I had no other modem to test against.
  
  As it turned out for me, the Arris is the reliable modem, and the CM3000 isn't. However, when the CM3000 does work, and did stay connected, it worked well.
  
  Also, issues took so long to show up, that I missed the return window from Best Buy, so I'm stuck with the CM3000, so I've decided to just keep it as a secondary modem to use for troubleshooting at this point, if I have issues with the Arris, or if I ever need a high split compatible modem.
  - MojoGene
    Tutor
    Jun 06, 2025
    To close out this thread, I replaced the CM3000 with an ARRIS SB8200 and I am now on the 6th day of flawless performance with not one disconnect. The circumstantial evidence suggests that the CM3000 does not, at least on occasion, play well with Cox internet service. This issue should be marked UNRESOLVED.
MojoGene
Tutor
May 30, 2025
Cable Firmware Version V6.01.03
MojoGene
Tutor
May 30, 2025
Thanks. The advice from the Cox service rep yesterday was that the modem was at fault. i have requested an elevation of the issue to a higher tier technician. Just curious as to whether my experience is unique or whether others have encountered this issue.
- FURRYe38
  Guru - Experienced User
  May 30, 2025
  What is the actual FW version #? Versions vary depending on ISP and released.

MojoGene

Tutor

May 30, 2025

Event Log:

Fri May 30 14:27:11 2025	(Critical (3))	No Ranging Response received - T3 time-out;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;
Fri May 30 14:25:42 2025	(Notice (6))	US profile assignment change. US Chan ID: 6; Previous Profile: 13; New Profile: 10 13.;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;
Fri May 30 14:25:29 2025	(Warning (5))	Dynamic Range Window violation
Fri May 30 14:25:29 2025	(Warning (5))	RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;
Fri May 30 14:25:24 2025	(Notice (6))	DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;
Fri May 30 14:25:22 2025	(Notice (6))	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;
Fri May 30 14:25:17 2025	(Notice (6))	TLV-11 - unrecognized OID;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;
Time Not Established	(Warning (5))	DHCP WARNING - Non-critical field invalid in response ;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:9a:d2:d2:dd:cb;CM-QOS=1.1;CM-VER=3.1;
Time Not Established	(Notice (6))	Honoring MDD; IP provisioning mode = IPv4
Time Not Established	(Critical (3))	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=54:07:7d:c6:e4:28;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

MojoGene
Tutor
May 30, 2025
Latest firmware is loaded.

Event
- FURRYe38
  Guru - Experienced User
  May 30, 2025
  What is the actual FW version #? Versions vary depending on ISP and released.
  
  Any Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem.

Forum Discussion

CM3000 Repeated Cox disconnects with SYNC Timing Synchronization failure