Comcast XFINITY → [Connectivity] Lost downstream and upstream bonding

Comcast HSI in Sacramento, CA 95831.

Been having problems with my modem staying connected for the past couple of months. Many times unscrewing the input coax to the Motorola SB6120 modem a few times would get it to connect again. So I finally got Comcast to send a truck out.

my wiring looks like this:
A) Port on Splitter/amp inside comcast dome -cable> B) 2-way Splitter in panel -cable> C1) Living Room -> D) Splitter -cable> E1) modem E2) Tivo HD

Before anything, the tech checked my model from his truck and said I had a "high Tax level," which I am not sure what he meant. Maybe high transmit level?

The tech clipped off and replaced the coax connectors at both ends of the cable between A and B and also the one at B end of the living room cable. He tested the signal at the jack in A, at the B cable end that come from the dome, and at the cable end C1 that feeds the living room splitter and the end of the E1 cable that feeds the modem. He said levels were good enough. When we reconnected my modem it synced up really fast and got 4 bonded downstream channels and 3 bonded upstream channels at between 48-50 dBmV. This was more than I ever got before and it seemed stable so we left it at that.

Later that evening, I noticed the blue lights indicating bonding had gone out so I checked the modem status page again. Single channel down and single channel up. Have not been able to get bonded up or down since yesterday. Wondering if they turned off bonding in my account or something. (how is that controlled?)

Any clues on what happened or what I should ask about?

i would assume he meant high Tx level....transmit but 50 upstream isnt that high...fairly normal...

bonding is controlled viz the cmts....nothing in the field, or that a tech could do would disable/enable it.

i would call in and ask what your upstream signal to noise (usnr) is....i would suspect it to be low (under 30) and that is whats causing your modem to drop its connection...

Unless you aren't tightening it properly, or are exposed to alot of ozone/chemical/??? it sounds like electrolisis or a bad ground is causing excess corrosion
ask that they check the ground and replace any bad/non-standard fittings.
Also if the modem could be on its own line from the first split it might avoid any leakage from other gear

here is the stats from the current connection. does this indicate anything? i wish i'd grabbed the data from when I had 4 down/3 up.

Downstream Bonding Channel Value
Channel ID 80
Frequency 555000000 Hz
Signal to Noise Ratio 36 dB
Downstream Modulation QAM256
Power Level
The Downstream Power Level reading is a snapshot taken at the time this page was requested. Please Reload/Refresh this Page for a new reading
-1 dBmV

Upstream Bonding Channel Value
Channel ID 1
Frequency 30600000 Hz
Ranging Service ID 126
Symbol Rate 5.120 Msym/sec
Power Level 51 dBmV
Upstream Modulation [3] QPSK
[3] 64QAM

Ranging Status Success
Signal Stats (Codewords) Bonding Channel Value
Channel ID 80
Total Unerrored Codewords 196164138
Total Correctable Codewords 2
Total Uncorrectable Codewords 1370

I am not in a position to interpret your line stats but I do have a SB6120 in Sacramento with Comcast. I experience a spontaneous going from blue to green indicating the loss of bonding. I power cycle the modem and I go back to blue. I only have HSI so there are no splitters at my end. Perhaps the problem is more global with Comcast or a failure of the SB6120. Since every speedtest I run shows no difference green or blue and none of the multiple devices which are always connected including VOiP, from a different provider, have any issues I figured I would leave well enough alone. Will say the 6120 is faster than my old 2.0 modem green or blue.

No matter what else is going on in your area, it is very likely that the 51 dB on the upstream is pointing at current or future trouble,
Call for a tech, and let them work on it in person.
(as gar187er said it may actually be the noise level, but rather than guess, call the local expert)

51 Dbmv is high for the upstream. That is the highst you want to go within the spec. 52 dBmV is the max I think for QAM64. I would get a tech.

why would transmit levels be high? isn't that controlled by the local modem? the tech did imply that since he checked all the levels on the line as ok, it could be my modem that was having the problem, but AFAIK, this is a good model of modem and it's less than a year old, so why would it be going wrong in this manner?

Could be a bad splitter as well, any of the connectors between the modem and tap, cable from their line to your house could be bad (if aerial, squirrels love to eat it, if underground it could have been nicked and damaged). But if he got blue lights I'm sure he was packing up and running away.

Yes the upstream is how "loud"/how much power YOUR modem is outputing. But it gets it's commands to raise or lower that power from the CMTS. The CMTS raises it just enough, until it can hear your modem clearly, so a high upstream can mean a lot of 'resistance' (old cable, splitters, and total footage) and /or NOISE(electrical) So having a high level doesn't mean a defective modem, just on that's working hard, near it's design limit.
Getting whatever properly fixed will make your modem last longer AND avoid problems day to day.

54 is the max...51 is well within reason....

Variables variables..

I'm currently at 51dBmv upstream, I have 3 upstream channels bonded, and the connection is solid. But this is not typical.

More usual is 55dBmv, at that point there are no more bonded upstream channels and the connection becomes a bit unstable. When it gets to 57dBvm, it's like a yo-yo, up and down.

On the other, shorter coax coming into the back of the house, I see 45dBmv upstream, but that's not where I need the modem.

Comcast did a line test on the flaky line, which is nearing 20 years old, and said it was "horrible" and a tech is coming out on Tuesday.

The only issue is will he run new coax free of charge, and if not how much will it cost.

I could plug the modem in on the shorter 45dBmv line and get a pair of power line ethernet adapters to get it over to the room where the bad line comes in but that's such a huge kludge.

We'll see.

Try posting in the Comcast direct forum. They may be able to enable channel bonding as they have done it for me in the past. Also for the upstream bonding it may depend on your speed tier. When I had Extreme 50, I had upstream bonding but when I downgraded back to Blast, I kept downstream bonding but lost upstream bonding.

Could also be a signal issue or outside plant issue (most likely) or a faulty modem (least likely). Also if you've had any thunderstorms lately (it's the season for thunderstorms), the cable plant may have been hit by lightning and that can mess things up. I personally have only had one modem fail and that was a Toshiba PCX 1100u back in 2004 and I think it was a power or cable line surge. Other than that, I've replaced modems as they've became obsolete. My current modem is a 6120.

Depends if it's a drop or inside wiring. In my area it's about $25 to install a cable outlet if the problem is inside wiring plus a trip charge for a customer side problem. If its a drop line (from the pole/pedestal to the ground block) they'll replace it free of charge. I live in a duplex and my underground drop line went bad and they replaced it free of charge although they did a poor job and they cut corners.

Well, the tech said it will be no charge, but I'll believe that when the next bill gets here.

He explained it much as you did, but I don't know what a ground block is.

The cables here run from the pedestal along the outside of the foundation and penetrate the walls where needed. There are no jacks, the cable comes in and goes where needed in the room. There are plastic grommets placed on the cable on both sides of the wall.

It needed to run under a walkway made of pavers. He said he couldn't rip them up, so I did that for him and replaced them when he got past that point. Did a great job, no corners cut at all.

Signal now is great, not a single drop, not even a single correctable or uncorrectable since Tuesday.