Modem: uncorrectables, T3/T4 errors

[ArneH]

Hello Everyone,

We had an ARRIS SB6183 modem. Two years back we started getting random disconnects on our modem (coincidentally around the time they put in a new gas pipe in the street, which might be unconnected).

Over the years this progressed worse until the extend we had daily disconnects (most of them during the night or early morning).

Sometimes it went back with a soft reboot, at other times we had to factory reset our modem and after reconnecting the connection was stable till the next disconnect. I also started taking notice of the modem event log. I am currently going for a bachelor degree in cybersecurity and networking, so I am learning fast. I noticed there are a lot of T3 and T4 errors and sometimes even T5 and T6.

We went through every hoop of retightening every connection. We also removed all splitters. There was on near the cable outlet in the wall near the modem, and one in the comcast box.

There used to be an 6 or 8way splitter (previous homeowner wanted cable tv in every room in there before a technician actually took it and replaced it with a 2 splitter. We are pretty sure that was not his splitter and he just took it for it's value, but that was a few years back before we had knowledge what is really was)

So currently there are no splitters what so ever. The incoming line in the comcast line, goes directly into the cable connected to box to the cable outlet where the modem connects to. The coaxel cable from the modem to the wall outlet has been replaced (several times and now has a brand new one). We still have some splitters (not golden as I read before that's important) if needed. We even got a new one (silver from commscope) with the new comcast streaming device we have not yet set-up.

Against better judgement, as it's know helpdesk blames faulty modems first, we replaced our modem with an ARRIS SB8200. Our old modem was 4-5 years old, so that's pretty aged, but I rather had waited until DOCSIS 4.0 is out, but I digress.

Yesterday we activated the new modem. So far no disconnect noticed (maybe it did, and it fixed itself when we were asleep). But dispite that there are reasons for concern. Even after one day there were correctables/uncorrectables. Even the eventlog is filled up. After the last event 7/29 16:29pm I factory reset the new modems to bring the correctables/incorrectables down to 0 and see what it would do in a day. They are filled up again (see screenshots below). I am concerned even despite no noticable disconnect yet, it's only a matter of time.

Before on my old modem, and new modem all the SNR and Power levels were all inside the ARRIS recommended parameters

Yet today I noticed the last upstream channel is 52.0 dBmV, 1dBmV above the recommended. This is new.

My question is: anyone have an inkling what might be going on? My first and still current thought is that there is a problem with the comcast line that runs from the ped to the box on the side of the house (noise?).
Any suggestions what I should do? I heard about attentuators if the dBmV is too high, but honestly I am unfamiliar with them and it's only one upstream channel. I don't want it negatively impacting downstream or other channels (if that's a possibility). Would a splitter, that we have plentiful now, do the same trick?
Yesterday, before I noticed the surplus in dBmV, I was even considering getting  a splitter with an active return.  Luckily it was unavailable. I now think it would have done nothing.

I want to exhaust every avenue before calling in a tech. Currently it's probably a pain to get a tech over due to the pandemic and we want to avoid possible charges. So any advise is welcome.

7-29 549pm - 1 (status)
7-29 549pm - 2 (event log)
7-30 133pm (status)
no new events logged.

Note: I have found other topics with similar problems. I believe most confirmed my susicion, but a lot of topics don't get updated by the OP when the problem is solved. I promise I will update this.
Note 2: I am aware the 159 channel might be a wrong read due to a firmware issue.

[EG]

You DO NOT want to add attenuation to the line. That will only make the upstream power go higher (worse), not lower. Attenuators will reduce the downstream power but will raise the upstream in the process. The modem's power levels work exactly opposite of each other. It becomes a balancing act.

So the goal to reduce the amount of overall line attenuation. If more work on the line / hardware doesn't improve anything, then an amp with active return may be tried / needed. But amps are to be used only as a last resort (band-aid) fix as sometimes they can actually make things worse (garbage in equals even more garbage out). It may be best to get a tech out to determine what is needed to properly balance the line. Good luck !

[ArneH]

Thank you for your advise. I have yet to call in a technician. I wanted to observe the new modem over the weekend.

1. Here are my observations so far: no noticable disconnect yet. If it happened, it fixed itself before we noticed.
2. Despite the power being high on the last upstream channel, my next two observations it showed a decrease to 50dBmv and even last 49dBmv.

3. There are additional correctables and uncorrectables.

I can't make any sense of this anymore.
Some questions I have:

1. With the decrease in upstream dBmv it's in normal parameters now. Do you still think it's a line balancing issue?
2. Is it normal behavior for the dBmV to fluctuate like this?

3. Despite no noticed disconnects, the amount of correctables/incorrectables is worrying and an indication something is wrong and future disconnect troubles might arise again, correct? The modem is newly installed only a couple days ago. I noticed this morning there were new T3 messages, not in the evening though.
4. Is the fifth upstream channel supposed to have that less width compared to the others?

Again I am kinda at a loss here. I know a tech will likely be needed. I am just hoping that I can steer him in the right direction, avoiding the process dragging on for months (which I know happens).

7-31 849am - 1 (status)

7-31 849am - 2 (event log)

7-31 1000pm - 1 (status)

[Bill Milosz]

Have you got 75 ohm terminators on every open F connector port in your "cable plant?" All the comast wall outlets, if not in use, should have a terminator, and any unused splitter port as well. THis probably isn't your issue, but it's considered a "best practice" to terminate all lines in their characteristic impedance to prevent reflections.

But I bet it's a Comcast line problem.  Som corroded connctor someplace. Or a line amp that has drifted below spec.

I would not be too concerned about stuff in the log, the logs can be quite verbose- as long as you are seeing good quality IP communications.  No packet loss, no loss of connectivity, modem constantly rebooting itself, extreme latency, excess jitter, etc.  Do a bunch of line quality tests ( https://packetlosstest.com/ etc) and see if there is a pattern -  in my case, it seems that during "peak" hours - right after 5 or 6 O'Clock - the service isn't quite as good. But I think that is to be expected.  In the middle of the night it is fine.

Once you have some data on line quality, then make your decision on whether or not to call in Comcast.

[EG]

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@ArneH wrote:

Thank you for your advise. I have yet to call in a technician. I wanted to observe the new modem over the weekend.

1. Here are my observations so far: no noticable disconnect yet. If it happened, it fixed itself before we noticed.
2. Despite the power being high on the last upstream channel, my next two observations it showed a decrease to 50dBmv and even last 49dBmv.

3. There are additional correctables and uncorrectables.

I can't make any sense of this anymore.
Some questions I have:

1. With the decrease in upstream dBmv it's in normal parameters now. Do you still think it's a line balancing issue?

Still would be but to lesser extent.

2. Is it normal behavior for the dBmV to fluctuate like this?

It should only fluctuate 3-4 dB. Any more is a problem.

3. Despite no noticed disconnects, the amount of correctables/incorrectables is worrying and an indication something is wrong and future disconnect troubles might arise again, correct?

Yes.

4. Is the fifth upstream channel supposed to have that less width compared to the others?

Yes. It's normal.

Again I am kinda at a loss here. I know a tech will likely be needed. I am just hoping that I can steer him in the right direction, avoiding the process dragging on for months (which I know happens).

7-31 849am - 1 (status)

7-31 849am - 2 (event log)

7-31 1000pm - 1 (status)

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If this is beyond your skillset, then get a tech out !

Bear in mind that if the premises facing techs can not find or fix a problem at your home, it is they who are responsible for escalating it to their line / network / maintenance dept. techs. The problem may lie beyond your home in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home.

Good luck with it !