Internet keeps dropping

I have my own Netgear CM3000 and when it's connected the speed is plenty fast (I have an 800mps plan). However, my internet drops multiple times per day and this has been going on regularly for the past few weeks. We've had service at this address for 12 years (and with this modem for at least a year) and it hasn't been an issue until recently. It only drops for less than 30 seconds, but it's enough to drop my work calls and interrupt tv (I use a non-comcast streaming service). We had a tech out last week who removed an old amp from our line and said our modem was green, but the internet dropped again within 30 minutes of him leaving - and another 5 times that night! At this point our internet is so unreliable I'm researching alternative options, but fiber isn't available in my neighborhood yet.

I looked at my modem log and there seem to be a lot of T3 timeouts, which from these forums seem to suggest there is something wrong further up the line on the Comcast side? This is the log just from today:

Time	Priority	Description
Wed Jun 04 15:38:28 2025	(Notice (6))	CM-STATUS message sent. Event Type Code: 16; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 14:34:35 2025	(Critical (3))	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 13:42:46 2025	(Critical (3))	SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 13:42:44 2025	(Critical (3))	No Ranging Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 11:26:45 2025	(Critical (3))	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 08:29:35 2025	(Notice (6))	US profile assignment change. US Chan ID: 41; Previous Profile: 13; New Profile: 12 13.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 08:29:30 2025	(Notice (6))	DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 08:29:29 2025	(Notice (6))	DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 08:29:24 2025	(Notice (6))	TLV-11 - unrecognized OID;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Time Not Established	(Notice (6))	Honoring MDD; IP provisioning mode = IPv6
Time Not Established	(Critical (3))	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 08:26:29 2025	(Critical (3))	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;
Wed Jun 04 03:46:48 2025	(Critical (3))	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=xx:xx:xx:xx:xx:xx;CM-QOS=1.1;CM-VER=3.1;

Any help is appreciated!

Responses

EG

Expert

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110.8K Messages

2 days ago

@user_shp9gc

What do the modem's signal status values look like ?

Please also copy all of the text in its entirety of the *Downstream Power Levels*, the *SNR's* (Signal to Noise Ratios), and the *Upstream Power Level* numbers and paste them into your next post.

Is there a router / WiFi in the mix here ?

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user_shp9gc

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3 Messages

Thanks for your response. I tried to reply quicker but lost internet while pasting in the values. There is a router in play - I use an Asus Zen AX/Mesh system which I've had for a few years without incident.

Here are the modem stats:

Downstream Bonded Channels

Channel	Lock Status	Modulation	Channel ID	Frequency	Power	SNR	Correctables	Uncorrectables
1	Locked	QAM256	28	543000000 Hz	2.1 dBmV	43.4 dB	0	0
2	Locked	QAM256	13	453000000 Hz	1.8 dBmV	43.2 dB	0	0
3	Locked	QAM256	14	459000000 Hz	1.8 dBmV	43.2 dB	0	0
4	Locked	QAM256	15	465000000 Hz	1.9 dBmV	43.3 dB	0	0
5	Locked	QAM256	16	471000000 Hz	2.1 dBmV	43.4 dB	0	0
6	Locked	QAM256	17	477000000 Hz	2.3 dBmV	43.5 dB	0	0
7	Locked	QAM256	18	483000000 Hz	2.4 dBmV	43.5 dB	0	0
8	Locked	QAM256	19	489000000 Hz	2.4 dBmV	43.5 dB	0	0
9	Locked	QAM256	20	495000000 Hz	2.5 dBmV	43.5 dB	0	0
10	Locked	QAM256	21	501000000 Hz	2.5 dBmV	43.5 dB	0	0
11	Locked	QAM256	22	507000000 Hz	2.5 dBmV	43.6 dB	0	0
12	Locked	QAM256	23	513000000 Hz	2.2 dBmV	43.4 dB	0	0
13	Locked	QAM256	24	519000000 Hz	2.2 dBmV	43.4 dB	0	0
14	Locked	QAM256	25	525000000 Hz	2.1 dBmV	43.4 dB	0	0
15	Locked	QAM256	26	531000000 Hz	2.1 dBmV	43.4 dB	0	0
16	Locked	QAM256	27	537000000 Hz	1.9 dBmV	43.3 dB	0	0
17	Locked	QAM256	29	549000000 Hz	2.2 dBmV	43.4 dB	0	0
18	Locked	QAM256	30	555000000 Hz	2.2 dBmV	43.4 dB	0	0
19	Locked	QAM256	31	561000000 Hz	2.3 dBmV	43.4 dB	0	0
20	Locked	QAM256	32	567000000 Hz	2.4 dBmV	43.5 dB	0	0
21	Locked	QAM256	33	573000000 Hz	2.7 dBmV	43.6 dB	0	0
22	Locked	QAM256	34	579000000 Hz	2.8 dBmV	43.6 dB	0	0
23	Locked	QAM256	35	585000000 Hz	3.1 dBmV	43.8 dB	0	0
24	Locked	QAM256	36	591000000 Hz	3.2 dBmV	43.9 dB	0	0
25	Locked	QAM256	37	597000000 Hz	3.4 dBmV	43.9 dB	0	0
26	Locked	QAM256	38	603000000 Hz	3.3 dBmV	43.9 dB	0	0
27	Locked	QAM256	39	609000000 Hz	3.1 dBmV	43.8 dB	0	0
28	Locked	QAM256	40	615000000 Hz	3.1 dBmV	43.8 dB	0	0
29	Locked	QAM256	41	621000000 Hz	2.9 dBmV	43.6 dB	0	0
30	Locked	QAM256	42	627000000 Hz	3.0 dBmV	43.7 dB	0	0
31	Locked	QAM256	43	633000000 Hz	2.7 dBmV	43.5 dB	0	0
32	Locked	QAM256	44	639000000 Hz	2.6 dBmV	43.2 dB	0	0

Upstream Bonded Channels

Channel	Lock Status	US Channel Type	Channel ID	Symbol Rate	Frequency	Power
1	Locked	ATDMA	2	5120 Ksym/sec	22800000 Hz	48.3 dBmV
2	Locked	ATDMA	3	5120 Ksym/sec	29200000 Hz	48.3 dBmV
3	Locked	ATDMA	4	5120 Ksym/sec	35600000 Hz	48.5 dBmV
4	Locked	ATDMA	1	5120 Ksym/sec	16400000 Hz	48.3 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	690000000 Hz	2.58 dBmV	42.9 dB	388 ~ 3707	388601887	281681289	0
2	Locked	0 ,1 ,2 ,3	194	957000000 Hz	-2.92 dBmV	40.1 dB	148 ~ 3947	390580138	327378591	82

Upstream OFDMA Channels

Channel	Lock Status	Modulation / Profile ID	Channel ID	Frequency	Power
1	Locked	12 ,13	41	36200000 Hz	43.5 dBmV
2	Not Locked	0	0	0 Hz	0 dBmV

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2 days ago

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user_shp9gc

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3 Messages

Here is the overall status:

Cable Diagnostic

Status: Good

Action:
Your setup looks fine. If you can't access the internet, make sure you properly activated the modem. If modem has been activated and you still can't access the internet, contact your service provider for troubleshooting help.
If you can access the internet but has other internet issue, the Netgear Cable Knowledge Base can provide additional troubleshooting info.

CM Status: Green

Downstream Status: Green

Downstream Power Level: Green
Downstream SNR: Green

Upstream Status:

Upstream Power Level: Green

(edited)

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2 days ago

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user_shp9gc

Internet keeps dropping

EG

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