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Not getting gigabit, stuck at 30mb/s, Low SNR on channel 159, issues with SB8200

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New Poster

Not getting gigabit, stuck at 30mb/s, Low SNR on channel 159, issues with SB8200

Hi all,

 

I recently bought a new modem (SB8200) to fully utilize gigabit connection with my Alien Amplifi router.

 

I called Comcast to provision the new modem, which worked fine, after which I upgraded my speed from 175 mb/s to 1000 mb/s. Shortly after that, I received a jump in speed up to 700-900 mb/s, which was great. However, after power cycling a couple of times (suggested by support), once reconnected, I only received 30 mb/s. After many cycles and resets, I'm stuck at 30 mb/s. However, in the evening, my speed somehow jumped back to gigabit speed, and I cancelled my technician visit, as I thought it just took time to propogate. 

 

Cut to this morning, I'm back to 30 mb/s. Many cycles and resets later, still the same. 

 

Another issue I'm noticing is that a direct connection from modem to computer, I can't connect to the internet - only if I connect my router. I've tried multiple computers, but no WAN IP is being assigned.  This is a brand new modem. 

 

When I check my modem stats, this is what I'm seeing:

 

30LockedQAM256669000000 Hz4.0 dBmV41.9 dB24725
31LockedQAM256675000000 Hz4.0 dBmV41.2 dB15749
32LockedQAM256681000000 Hz4.1 dBmV42.0 dB30
159LockedOther722000000 Hz5.5 dBmV19.0 dB876124470

139346

 

I know 19.0 dB is low for channel 159, which is the gigabit channel. Any reason for this/can I improve this? Or do I require a technician visit?

 

I'm going to try some more modem troubleshooting.

 

*EDIT*

I've successfully connected directly to the modem via ethernet after cycling while connected - still 30mb/s.  

Here's my most recent speedtest, wired to modem via cat6: https://www.speedtest.net/result/10102150568

At least I now know for sure that it isn't my router.

 

*EDIT 2*

Found a shorter coax, replaced it, and got high speeds again yay! But then, 20 minutes later, it slowly dropped to around 200, and now I'm back at 30 mb/s. Wonderful.

 

30LockedQAM256669000000 Hz3.9 dBmV42.0 dB190
31LockedQAM256675000000 Hz4.0 dBmV41.3 dB220
32LockedQAM256681000000 Hz4.0 dBmV41.9 dB70
159LockedOther722000000 Hz5.7 dBmV24.0 dB1044275463158

 

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New Poster

Re: Not getting gigabit, stuck at 30mb/s, Low SNR on channel 159, issues with SB8200

I just noticed a recent disconnect in service over night around 1a which typically means some maintenance has been done.  After that, we can only pull between 27-35Mbits.  Same exact issue as you with the SB8200 and no power on channel 159.

 

Did you get a resolution?

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New Poster

Re: Not getting gigabit, stuck at 30mb/s, Low SNR on channel 159, issues with SB8200

I just had a relatively successful conversation with a higher level technician.  They have started monitoring my modem and have guaranteed me that this issue will be resolved my end of day today.  Thanks for creating this post as it gave me the fuel I needed to say "This isn't just me..."

 

I was surprised to hear the technician I spoke to didn't even know that Comcast pushes their own firmware for 3rd party modems..... They were trying to offload me onto Arris support which wouldn't have spoken to me because the modem is now out of warranty.  Gotta stick to your guns with these guys or nothing gets done......

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Expert

Re: Not getting gigabit, stuck at 30mb/s, Low SNR on channel 159, issues with SB8200

This is not to say that something isn't wrong, but FWIW, channel 159 is the DOCSIS 3.1 / OFDM channel for the gigabit speeds. There is a known glitch with some makes / models of modem's firmware where the measuring mechanism incorrectly reads the power level, the SNR, and the bit errors for that channel. So it reads many errors when there really aren't. 

 

Good luck !



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New Poster

Re: Not getting gigabit, stuck at 30mb/s, Low SNR on channel 159, issues with SB8200

Yes, can comfirm that channel 159 always looks a bit suspect with high errors but I've never seen it with 0 errors and 0 SNR.  Usually the SNR reports normal as the other channels do.  I guess this is sort of like a Volkswagen, you only have to worry when the CEL turns OFF.  😄  All's well when it's reporting errors.