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A few bad channels on my modem -- what to do?

New Poster

A few bad channels on my modem -- what to do?

Hi - just upgraded to 1GB internet, and I'm only seeing about 30 down, 30 up (this is from a laptop over ethernet direct to the modem/gateway.)

Device is a Technicolor CGM4140COM, HW rev 2.2. No siginficant-seeming errors in the logs.

 

Connection info lists channels 1-32 (256 QAM) and a "159" (OFDM). All are locked, all have SNR of about 36-40 dB, power -6dBmV to 0.4dBmV, with the exception of channels 1, 2, and 3, which are "locked" but have 0 SNR, power -48.9dBmV through -29.9 dBmV, and "Unknown" modulation. Channel 4 has -12.9 dBmV and 36.8 dB SNR.

 

Upstream has two locked channels and two unlocked. Power levels 33 to 48dBmV.

 

Uncorrected codewords for `all indices are in the 8000 to 10000 range (except index 2, 3, and, 4, which have 0 of any type of codeword.)

 

Does this data explain my slow speeds? If so, what's the best course of action?

Any value in squirting some contact cleaner in the coax? Or is this more likely an issue with comcast itself? If it is a problem with comcast, they wouldn't ask me to pay them to fix it, right?

 

Thanks for any ideas.

 

Expert

Re: A few bad channels on my modem -- what to do?

Have you first tried power-cycling / re-starting the device ? No joy ? Try hard resetting the device to factory defaults by pressing and holding in the recessed reset button on the rear for 30 seconds. This can sometimes clear up some weird issues. You will lose any customized settings, and they will need to be re-configured from scratch if you do the latter.



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I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
New Poster

Re: A few bad channels on my modem -- what to do?

Thanks for that reply! I finally got around to poking at this. Rebooting the router had no effect. Resetting to factory settings and reconfiguring also had no effect. I'm still only seeing about 32 down / 36 up on our "1GB" internet service.

 

Any harm in unscrewing the coax and squirting some contact cleaner in there?

 

It's kind of a long run from the comcast box to the modem (maybe 60 feet) with one coupling in the middle. I was wondering if a bad connector might explain this?

 

New Poster

Re: A few bad channels on my modem -- what to do?

Here are the current channel values, in case they are of use; same type of results as before:

 

Index
29
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
30
31
32
159
 
Lock Status
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Frequency
663 MHz
483 MHz
489 MHz
495 MHz
507 MHz
513 MHz
519 MHz
525 MHz
531 MHz
543 MHz
549 MHz
555 MHz
561 MHz
567 MHz
573 MHz
579 MHz
585 MHz
591 MHz
597 MHz
603 MHz
609 MHz
615 MHz
621 MHz
627 MHz
633 MHz
639 MHz
645 MHz
651 MHz
657 MHz
669 MHz
675 MHz
681 MHz
722 MHz
629600000
SNR
39.9 dB
0.0 dB
0.0 dB
0.0 dB
37.6 dB
39.6 dB
40.2 dB
40.2 dB
40.3 dB
40.3 dB
40.2 dB
40.3 dB
40.3 dB
40.4 dB
40.4 dB
40.3 dB
40.3 dB
40.4 dB
40.4 dB
40.3 dB
40.2 dB
40.2 dB
40.4 dB
40.3 dB
40.4 dB
40.3 dB
40.1 dB
39.9 dB
40.0 dB
40.2 dB
39.9 dB
40.1 dB
39.8 dB
NA
Power Level
-2.0 dBmV
-47.7 dBmV
-37.6 dBmV
-28.8 dBmV
-11.0 dBmV
-6.3 dBmV
-4.4 dBmV
-3.4 dBmV
-2.5 dBmV
-2.6 dBmV
-2.7 dBmV
-2.1 dBmV
-1.7 dBmV
-1.7 dBmV
-1.6 dBmV
-1.9 dBmV
-1.9 dBmV
-1.6 dBmV
-1.4 dBmV
-1.0 dBmV
-1.5 dBmV
-1.7 dBmV
-1.1 dBmV
-1.4 dBmV
-1.3 dBmV
0.9 dBmV
-1.5 dBmV
-1.9 dBmV
-1.9 dBmV
-1.0 dBmV
0.5 dBmV
-1.1 dBmV
0.6 dBmV
NA
Modulation
256 QAM
Unknown
Unknown
Unknown
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
OFDM
OFDM

 

Upstream
Channel Bonding Value
Index
1
2
3
4
Lock Status
Locked
Locked
Not Locked
Not Locked
Frequency
30 MHz
36 MHz
17 MHz
23 MHz
Symbol Rate
5120
5120
5120
5120
Power Level
48.5 dBmV
47.0 dBmV
43.3 dBmV
46.3 dBmV
Modulation
QAM
QAM
QAM
QAM
Channel Type
ATDMA
ATDMA
ATDMA
ATDMA
Expert

Re: A few bad channels on my modem -- what to do?

You've got some borked downstream channels there / serious reverse cable tilt ! It may be best to get a tech out to investigate this one ! Good luck with it and please post back with how things turn out !



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
New Poster

Re: A few bad channels on my modem -- what to do?

Ok, comcast guy came out, and replaced the entire line from the pole to the house. Found corrosion in some splice at the pole, as well as a bad section right at the house. The channel values look "good" to me now (not that I'm an expert). Let me know if you see anything awry there.

 

I don't have a laptop with ethernet that was made in this century, so I'm struggling to test things to see if they are truly working; my iPhone 5S is getting ~85 down connecting to our internal router over 5GHz (Nighthawk R7000) so that seems nominal. I'll have to figure a way to really test it...

 

Meantime, though, at least the channel issues seem resolved? "uncorrectable Codewords" currently in the 1-2k range.

 

Index
1
2
3
4
Lock Status
Locked
Locked
Locked
Locked
Frequency
30 MHz
36 MHz
17 MHz
23 MHz
Symbol Rate
5120
5120
5120
5120
Power Level
45.3 dBmV
45.3 dBmV
45.8 dBmV
46.3 dBmV
Modulation
QAM
QAM
QAM
QAM
Channel Type
ATDMA
ATDMA
ATDMA
ATDMA

 

Index
21
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
22
23
24
25
26
27
28
29
30
31
32
159
 
Lock Status
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Frequency
615 MHz
483 MHz
489 MHz
495 MHz
507 MHz
513 MHz
519 MHz
525 MHz
531 MHz
543 MHz
549 MHz
555 MHz
561 MHz
567 MHz
573 MHz
579 MHz
585 MHz
591 MHz
597 MHz
603 MHz
609 MHz
621 MHz
627 MHz
633 MHz
639 MHz
645 MHz
651 MHz
657 MHz
663 MHz
669 MHz
675 MHz
681 MHz
722 MHz
629600000
SNR
39.2 dB
39.7 dB
39.8 dB
39.7 dB
39.9 dB
39.5 dB
39.8 dB
39.5 dB
39.5 dB
39.7 dB
39.6 dB
39.4 dB
39.4 dB
39.4 dB
39.5 dB
39.4 dB
39.5 dB
39.5 dB
39.3 dB
39.2 dB
39.1 dB
39.3 dB
39.2 dB
39.1 dB
39.0 dB
38.8 dB
38.9 dB
39.0 dB
39.0 dB
39.1 dB
38.9 dB
39.1 dB
38.9 dB
NA
Power Level
1.4 dBmV
1.7 dBmV
1.7 dBmV
1.6 dBmV
2.2 dBmV
2.1 dBmV
2.0 dBmV
1.7 dBmV
1.4 dBmV
1.6 dBmV
1.6 dBmV
1.5 dBmV
1.2 dBmV
0.9 dBmV
1.2 dBmV
1.4 dBmV
1.5 dBmV
1.6 dBmV
1.2 dBmV
1.4 dBmV
1.3 dBmV
2.1 dBmV
1.7 dBmV
1.5 dBmV
1.4 dBmV
0.9 dBmV
1.1 dBmV
1.5 dBmV
1.2 dBmV
1.6 dBmV
1.8 dBmV
1.4 dBmV
2.4 dBmV
NA
Modulation
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
OFDM
OFDM