Googling produces a variety of answers.

Got a SB5101U surfboard from the cable company (Metrocast). Been fine for nine months. Last week, it began randomly disconnecting me and re-connecting. The upstream power fluctuates between 47 dB and 54dB. 54 is near the clipping point, which is probably causing it.

I have touched nothing in any of the house wiring.

I took the damn thing outside and hooked up to the main line (to bypass all splitters and unions). Exact same result.

If a modem is failing, is this a possible symptom?

It also seems to be somewhat usage-based. When gaming, it tends to occur more often.

I'm taking it to the local store tomorrow to change it out. Just wondering if anyone has experience with this model or this symptom.

5/2/2011 8:39:05 PM

Now seems to be happening every 10 minutes or so.

Whenever it crashes it throws these entries in the logs:

Started Unicast Maintenance Ranging - No Response received - T3 time-out
Unicast Ranging Received Abort Response - Re- initializing MAC
Rng Rsp Abort Status - Reinitialize MAC...
DHCP FAILED - Requested Info not supported.

Also it seems like after each reset the upstream power gradually increases, linearly.

[Edited on May 2, 2011 at 9:53 PM. Reason : ]

5/2/2011 9:25:32 PM

sure does sound like it's the modem.

do you have digital cable? if so, find the diag mode on your cable box and look for the up/down power and the SNR that it's reporting, then connect your modem up to the same line and see what you get. they're connecting to the same OOB backend.

5/3/2011 5:57:07 AM

No, have DirecTV.

5/3/2011 7:58:23 AM

New modem holding rock steady at 46 dB upstream.

Too early to declare, but high confidence that modem was failing.

Beware the SB5101U.

5/3/2011 7:18:42 PM

if you removed the splitters and it was still maxing out, there is definitely something wrong with that picture. components fail sometimes, so sure it could have been just that.

also, electrical noise in a house can cause upstream issues (for you and anyone you share commons with), but since you removed all possibilities of that with a direct connection that shouldn't be part of the equation...

so yeah, i'd bank on either bad plant in your neighborhood or a bad cable modem, and it sounds like the new modem did the trick

5/6/2011 1:22:45 PM

Once or twice since the new modem installed, I have seen upstream exceed 53 dB. Possible issue with the neighborhood.

Or, since you mentioned in-house electronics...I have DirecTV. The coax from the sateillite goes into the house at the same point as the Cable coax. 6 inches from each other. I know the DirectV lines are at a higher voltage (last week they had to come and replace the union and connectors at the ingress point because it was charred black). Noise?

5/6/2011 2:38:54 PM

asked an expert for you, his response, which slightly contradicts mine, since noise is of course different from quality, so i was a bit incorrect in that:

---

Noise and ingress should not affect what the modem needs to transmit. The modem will transmit to overcome attenuation.

If it is charred black, then it could be ground loops between different grounding points (neighbor to neighbor, one side of house to another) in the USA, we are supposed to have a common bond of ground according to NEC or NESC with electric, cable, and phone so there are no differences of potential.

If he disconnects the coax and the lights fade or he gets shocked, that’s a good indication

5/6/2011 6:25:50 PM

Still happening. Gonna have to call the tech. Naturally, he'll say everything looks fine. Even though I state it's a random, instantaneous issue that won't reproduce itself until he leaves.

First world problems.

5/12/2011 11:13:01 PM

Quote :

"Or, since you mentioned in-house electronics...I have DirecTV. The coax from the sateillite goes into the house at the same point as the Cable coax. 6 inches from each other. I know the DirectV lines are at a higher voltage (last week they had to come and replace the union and connectors at the ingress point because it was charred black). Noise?"

lol no, i ran DirecTV and TWC signals on the same physical line using a diplexer and it worked great. definitely not your problem.

try just putting a coax splitter or two in between the wall plug and the modem. if it's really high upstream power, that should attenuate it a little.

[Edited on May 13, 2011 at 3:57 PM. Reason : :]

5/13/2011 3:56:27 PM

It's periodically peaking to 55 dB (and resetting) several times per day.

^ Everything I've read says to REMOVE splitters, as they'll push the needed upstream power higher.

On my wife's computer, her Windows time, which automatically syncs, is off by one hour. Whenever we manually adjust, a few hours later is wrong again.

After googling this could be due to a DNS server mis-assignment...something wrong on the ISP side. I don't know more than this...

Service guys coming Thursday.

[Edited on May 17, 2011 at 9:52 PM. Reason : ]

5/17/2011 9:52:08 PM