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New CM205V Interferes with TV Signal
When a CM2050V is connected to a three-way coax splitter (the modem, and two TVs to Xfinity Voice/Data/Cable television service, it disrupts the signal to the two tvs. Disconnect it, and the TVs are fine. Disconnect the standalone router, problem still exists. I rolled back to a Netgear C7100V in passthrough mode, and everything works again. The problem is definitely the modem. The only reason I bought this modem is because I received an email advising that Netgear will stop support for the C7100V on 7/31/25. Neither Comcast nor Netgear support can explain what's going on, much less make it work. Would be better to upgrade to CM2050V, but the C7100V will stay in place for now ANY ideas how to solve this problem? Thanks in advance.
Way too many correctable/uncorrectable errors for a 24 hour period of time.
DOCSIS 3.1 is backward compatible with DOCSIS 3.0. I do not think DOCSIS 3.1 is backward compatible with DOCSIS 2.0. If you are looking at DOCSIS 2.0 hardware, you want to check the coax type to ensure it is correct for the current DOCSIS 3.1 connections (RG6).
What were the upload/download throughputs with your new splitters in place?
You might find some ideas in chapter 3 of this reference: https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
42 Replies
Way too many correctable/uncorrectable errors for a 24 hour period of time.
DOCSIS 3.1 is backward compatible with DOCSIS 3.0. I do not think DOCSIS 3.1 is backward compatible with DOCSIS 2.0. If you are looking at DOCSIS 2.0 hardware, you want to check the coax type to ensure it is correct for the current DOCSIS 3.1 connections (RG6).
What were the upload/download throughputs with your new splitters in place?
You might find some ideas in chapter 3 of this reference: https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
Speedtest gives me 700+ Mbps upload and 40+ Mbps downloads, pretty much the same as before. Thanks for the article. Could this be them (Xfinity) and not me?
Could this be them (Xfinity) and not me?
I suppose it is possible, but very very difficult to determine and pin down when your are using a customer owned and maintained (COAM) modem. When a piece of COAM hardware is in the signal path, the ISP has no interest is what happens past that point.
New splitters cleaned things up but still had problems with occasional pixilation and anomalies in ever-changing areas of the screen. Rolled back to the old modem, things back to normal again. Report attached. Somehow this modem is not compatible with my system. Maybe it's the DOCSIS 2.0 cable boxes I use. Maybe it's something else. Couldn't get the new cable box to respond to the IR emitter connected to a legacy universal remote system, so that's not an option at present. Internet speeds are the same on the new and old modem. Thanks to all for your time and effort.
For both, power levels are good now for both, however both modems are seeing too many Correctables and Un-correctables.
The C series is DOCSIS 3.0 and the CM is 3.1.
Something maybe happening down the line after the modem.
One of the other big tells is the ofdma channels. Your normal ones are pretty much in range (ish). The ofdma has 1 channel barely in range and the other outside of it. Something is restricting its power levels. (which is why the docsis 3.0 device works fine but not the docsis 3.1 device) So its either the splitters or something in the line causing issues on those channels range.
Info as requested. Looks like an awful lot of errors...
Info as requested. Looks like an awful lot of errors...
Yes, but you cut off the part that would provide more of a complete picture. Such as the system up time. The correctable/uncorrectable values accumulate over time and reset to zero when your modem is rebooted. With the information you provided, no one knows the time frame.
I don't see an uptime stat on the report generated by the CM2050V. I see it in the cable modem stats on the C7100V, which is currently online (for 114 hours of Up Time, it shows errors in the low thousands on downstream channels 1-16 and does not provide error counts on upstream channels. The CM2050V is not online at present. When I try again next week, I'll try to get more useful info. Sorry about that. Thanks again.
Ya, tons of correctables and un-correctables that should be mostly zeros.
Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box.
Be sure your using good quality RG6 coax cable up to the modem.
Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
Be sure to power OFF the modem for 1 minute then back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Modems/m-p/1530376#M12853
https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
https://highspeed.tips/docsis-events/
Copy/paste not POSTING…
See above post for upstream/downstream info.
We want the actual values. Not the general info or log.
Copy/paste log info not working. Tried three times. Struck out. Tomorrow is another day. Thanks for your time and interest.
Please post a copy and paste of the modems connection status log page.
https://kb.netgear.com/30007/How-do-I-obtain-the-cable-connection-information-from-a-NETGEAR-cable-modem-modem-routerPlease post the data on that same page that is down farther. Please scroll down.
Got a screensnip of the cable connections that shows upstream/downstream info?
The C7100V is only docsis 3.0 vs the CM is a docsis 3.1 device. the recommendation from Kitsap could be right on in the interference issue.
I'd also try the double splitter before splitting for the cable tv connections. But a lot could depend on your signal that you have. Thats where that cable connections info comes in.
Look on the labels and make sure your splitters are capable of passing signals up to 1 GHz. Many older splitters cut off at 850 MHz. If the labels are gone, invest in some new splitters. Buy two with dual output. Connect the line in to one splitter with a connection out to your your modem. The second line out should go to your second splitter with outputs to the TVs.
I do not think there is a CM3050V, should be CM2050V. Are you connected to Xfinity?
Current splitter up to 900 mhz
How 'bout this one? (on amazon)
GE Digital 2-Way Coaxial Cable Splitter, 2.5 GHz 5-2500 MHz, RG6 Compatible, Works with HD TV, Satellite, High Speed Internet, Amplifier, Antenna, Gold Plated Connectors, Corrosion Resistant, 33526
Please post a copy and paste of the modems connection status log page.
Which ISP are you connected with?
Typos in title and post. CM2050V. Xfinity, formerly known as Comcast. Splitters work with C7100V. I'll give it a try in the next week, but I have my doubts. Why would the new modem require a new splitter? And why would an old splitter interfere with the cable TV signal only on the new modem??
Typos in title and post. CM2050V. Xfinity, formerly known as Comcast. Splitters work with C7100V. I'll give it a try in the next week, but I have my doubts. Why would the new modem require a new splitter? And why would an old splitter interfere with the cable TV signal only on the new modem??
Your new modem will connect to the Xfinity Enhanced Speed Network that runs up to 1 GHz. Your old modem would only connect to the Xfinity standard network that peaked at around 850 MHz. Your old splitter is blocking part of the spectrum your new modem is trying to work with and causing problems.
No need to waste $ on new splitters that are capable of going above 1 to 1.1 GHz.
Comcast washed their hands of it. As always in telecom, it's blame the other guy. The router is a new Synology model. Works great with the C7100V. For cable TV viewing, the TVs are not taking digital from the router. For web-based channels, they are and work perfectly. It's only the, what I beleve, is the lower frequency cable info that is getting garbled. There is a difference between the C7100V and the CM3050V that nobody seems to recognize.
There a model# for the Synology? Maybe the new router needs to be checked by the Mfr support people.
The different between the C7100V and CM modems are that CM series modems are only modems only, no router or wifi there. C series anything is a modem with built in router and wifi.
I'd get with Synology first and have them check there router with your TVs.
Does this do any good? Thanks again. By the way, the data side was working perfectly. But the TV screens were crazy, especially during a speed test. So, my guess would be that its data signal mixing with video signal somehow, but my knowledge of networking dates back to the days of two telephone couplers - one for send and one for receive.
Wed May 21 15:07:10 2025 Notice (6) CM-STATUS message sent. Event Type Code: 20; Chan ID: 193; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;
Wed May 21 15:03:48 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 1 2 3.
Wed May 21 15:03:07 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.
Wed May 21 15:02:49 2025 Notice (6) DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3.;
Wed May 21 15:02:49 2025 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;
Wed May 21 15:01:31 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 11 13; New Profile: 10 13.;
Wed May 21 15:00:31 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 10 13; New Profile: 11 13.;
Wed May 21 14:51:01 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 11 13; New Profile: 10 13
Wed May 21 14:50:31 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 10 13; New Profile: 11 13.;
Wed May 21 14:45:41 2025 Notice (6) CM-STATUS message sent. Event Type Code: 20; Chan ID: 193 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;
Wed May 21 14:45:27 2025 Warning (5) Dynamic Range Window violation
Wed May 21 14:45:27 2025 Warning (5) RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-
Wed May 21 14:42:49 2025 Notice (6) CM-STATUS message sent. Event Type Code: 20; Chan ID: 193; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID:
Wed May 21 14:42:46 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 11 13; New Profile:
Wed May 21 14:41:46 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 12 13; New Profile: 11 1
Wed May 21 14:41:29 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 1
Wed May 21 14:41:27 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID:
Wed May 21 14:41:07 2025 Notice (6) DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3
Wed May 21 14:41:06 2025 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;
Wed May 21 14:41:05 2025 Notice (6) TLV-11 - unrecognized OID;
Wed May 21 14:40:56 2025 Notice (6) Honoring MDD; IP provisioning mode = IPv6
Wed May 21 14:40:49 2025 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;
Wed May 21 14:39:14 2025 Warning (5) ToD request sent - No Response received;
Wed May 21 14:38:49 2025 Warning (5) MDD message timeout;
Wed May 21 14:36:33 2025 Notice (6) CM-STATUS message sent. Event Type Code: 20; Chan ID: 193 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;
Wed May 21 14:36:14 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Wed May 21 14:35:53 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193 194; DSID: N/A
Wed May 21 14:35:53 2025 Notice (6) CM-STATUS message sent. Event Type Code: 20; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A
Wed May 21 14:35:35 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193 194; DSID: N/A; MAC Addr: N/AWed May 21 14:35:25 2025 Notice (6) CM-STATUS mehan ID: 193 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3
Wed May 21 14:34:47 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.
Wed May 21 14:34:43 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.
Wed May 21 14:34:32 2025 Notice (6) DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=;
Wed May 21 14:34:32 2025 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;
Wed May 21 14:33:46 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 11 13; New Profile: QOS=1.1;CM-VER=3.1;
Wed May 21 14:32:46 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 10 13; New Profile: 11 13.;CM-QOS=1.1;CM-VER=3.1;
Wed May 21 14:24:46 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 11 13; New Profile: 10 13.;CM-
Wed May 21 14:23:31 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 12 13; New Profile: 11 13.;CM
Wed May 21 14:22:46 2025 Notice (6) US profile assignment change. US Chan ID: 41; Previous Profile: 10 13; New Profile: 12 13.;CM-QOS=1.1;CM-VER=3.1;
Wed May 21 14:15:10 2025 Notice (6) CM-STATUS message sent. Event Type Code: 5; Chan ID: 5; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA ProfileCM-QOS=1.1;CM-VER=3.1;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.
Still need to see rest of cable connections page.What brand and model# router is connected to the CM modem?
Do you have TV services with the ISP or just streaming TV to the TVs with the host WiFI router?
