MB8611 OFDM PLC pwr (dBmv) too low

... MB8611 has been "going down" or restarting 3-6 times per day ...

The OFDM downstream channel is indeed out of spec, the QAM downstream channels are lowish to borderline/out of spec, and the upstream channel power levels are higher than we would like to see them. Network connection like this are often due to poor coax connections or damaged coax cable, usually in or near your home. Running the cable through a surge protector, a defective splitter, or too many splitters can cause signal problems as well. If there is an amplifier in the line make sure it's getting power. 

If you want to troubleshoot this yourself, please see Internet Troubleshooting Tips. If you can't find the problem or you'd rather have Comcast take care of it and an employee does not respond to your message here, call them at the phone number on your bill or 1-800-Comcast, or use one of the options on https://www.xfinity.com/support/contact-us/. It's not likely they can fix the problem remotely. If not, insist they send a tech out to identify the cause and correct it.

If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit (approx $100) unless you have their Service Protection Plan ( https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast rental device or anything outside your home you shouldn't be charged.

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Hi,

I have exact the same problem with my MB8611 on 1Gbps-speed plan.

All 32 QAM channels have average -4 to -6dBmV signal levels, SNR over 38dB ,but the OFDM channel’s  only has -18dBmV with ~31dB SNR. The discrepancy of signal strength between QAM and OFDM is over 12dBmV. OFDM got tons of uncorrectables and once that number hits the limit it will trigger the reboot….

Any findings on your case ? Looks to me the OFDM coming out form Comcast CMTS is not that great at those 957Mhz range..

@user_5fb81w 

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@user_5fb81w @XfinityArmand 

Please circle back here and post any possible solutions for the issue here in these open forums so that all readers here may benefit from the exchange / info. This is in keeping with the spirit for which these public help forums were originally intended. Thank you.

No solution yet so far.

First tech(Comcast “contractor”) on-site Thursday put the blame on the modem(MB8611)I have  is not on Comcast so-called  “Genes network project” or something( I guess it’s referring to 10G plan) and I told him I only on 1Gbps plan.

2nd tech(from Comcast) come after I insisted and did ran OFDM check on signal coming into my house and saw some red so he ordered a ticket to their “network team” to replace a network box located across the street.

After that , there is an overall ~2.5dBmV improvement of signal power across all QAM and OFDM channels but the discrepancy between the two still >11 to 12 dBmV and interruptions still exit.

Looks to me MB8611’s OFDM is operating at 957Mhz range , some what bit  higher than some of the other “10G” certified modem which OFDM is around 7XXMhz closing to QAM channels. 

Need Comcast expertises on this forum to chime in provide some insights and/or possible cause and solutions, put some amp somewhere along the path in CMTS?

Problem(internet connection on/off) still exit.

Modem still show low signal level ONLY on OFDM channel, at ~-17dBmV , SNR ~30, tons of correctables & uncorrectables.

Is it Really that MB8611 and Comcast so-called “10G” network does not work together any more ? 

Looks like there are there is a spike of Mb8611 connection drop complains on this forum starting this year since 10G roll out.

There is only one splitter (brand name Extreme 5-1002Mhz) installed by Comcast before ,one output to cable TV, one to modem.

OFDM (957Mhz) number is way too low (-18dBmV), probably not by roll off from splitter.

All other QAM256 channels are on the low side also , -4 or 5dBmV at ~400/500Mhz, and then ~8dBmV when it close to 700Mhz.

Seems like signal is still kind of sloppy for all spectrum before going into the house as tech on-site tested(shown some red) weeks ago.

Not sure whether Comcast can pull those data remotely and adjust the signal level(amp) along the path of their HFC network before going into the house.

Surprisingly got a voicemail call on this Saturday, presumably from Comcast(510-856-2010) saying:

  We are calling to advise your that our technicians identified and corrected an issue related to the service problem that you reported......

Check back modem signal power level, every channel (QAM256 and OFDM) ALL up by ~12dBmV! and no more uncorrectable codes on OFDM channel anymore!

Although the power level discrepancy between QAM channels Vs OFDM still ~10dBmV ( +5 dBmV for QAM Vs ~-5.X dBmV for OFDM) , there is no internet drop so far.

No details mentioned in the voicemail what Xfinify did on the drop and headend.