Motorola SB5100 disconnect issue

AgrFan

[H]ard DCOTM x2
Joined
Sep 29, 2007
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I have a Motorola SB5100 cable modem that disconnects alot. Power-cycling usually gets it functioning again. Speeds are good when is stays connected. The upstream power level is showing 0dBmV on the Signal page. It won't download the latest config file / firmware from Comcast. I'm getting the right config file but "SW File Corruption" appears in the modem log after it's downloaded. I've been running old settings for quite some time with no issues until now. Comcast can't figure it out. They're saying the modem is defective and needs to be replaced. Motorola says they don't handle these issues and to contact Comcast. I switched it out with a brand new SB5101 and everything is fine.

Anybody see this before?
I really hate to replace the modem if this is some sort of software issue...
 
Over 90% of the time, when I come across a problematic cable connection...it's due to a "bad splitter"....or...too many splitters setup for the coax in the house or improperly setup.

But...in your case, since you say you tried swapping out the modem and the replacement worked fine....then I'd say you've without question found the problem...a bad modem. Case already solved.
 
Well, the new SB5101 disconnected me last night. The only way I could get back online was to power-cycle the modem and the router. I have Comcast coming out this Friday. The person I talked to this morning checked the signal levels and indicated the upstream transmit level is out of spec (too high). If that fixes the problem, I'm switching back to the old SB5100 and the new SB5101 is going back to Best Buy.
 
From my experience with Comcast...(quite a bit)....the techs are good when they come out.

Things to check for...first, of course...your connection from the street, to your house/building.

From there...it's commonly in the splitters. Especially if your splitter is outside...you'll commonly have to replace an outside splitter every year. Ideally, have any splitters inside.

If you need quite a bit of splitting..say you have many TVs/lines to rooms in the house, you'll want one splitter at the top....a 2 way splitter, as close as possible to where the line from the street comes into your house. Have one of the outgoing go to the line to your modem, the other to another splitter...which goes to all your TVs/lines.

So basically your modem line should be the first device...at the top of the splitting pyramid sort of speak.
 
OK i work in the cable industry there can be two things wrong . first either your modem is shot. second your signal levels at your modem are toast. I don't know how many of these i have fixed in my life but here goes. YOU CAN NOT SPLIT THE MODEM CABLE FOR A TV. And thats that I'm not yelling at you just making sure you pay attention. The line for your modem must be a home run line all the way to the first splitter in your house if it's not it will go on and off all the time like you are experiencing. Alot of people after the cable installer leaves puts a splitter on the end of the modem line and try to split the TV next to there PC into the same line NONONO doesn't work that way if you want a TV line there run one. I'm not saying that it always cause outages on your modem but 95% of the time it does. Another thing if you install your own cable DO NOT USE screw on fittings they are garbage. Second gold connectors are junk if its gold throw it away this goes for splitters to buy one thats silver. You will never see a com cast or time warner tech using a gold fitting or splitter there is a reason for this.
 
I got a call tonight from a tech guy at the local Comcast office checking to see if I was still having issues. I finally found out my area is being upgraded to DOCSIS 3.0. There have been issues over the past few weeks upgrading the CMTS that serves the Kennett Square, PA area. I'm still going to have my signals checked anyway. I haven't had any disconnects with the new modem since Monday night.
 
I have one 4-way splitter (silver) inside the house ... 1 output goes directly to the modem ... 2 outputs go to TVs ... 1 output is not used.
 
I'd probably switch out the 4-way splitter for one 2-way splitter (one leg going to your modem, next leg going to the tvs), and one 2 or 3-way splitter for the tvs. In the meantime, check the splitter and see if it has balanced losses on each leg. There should be markings saying XdB or -XdB (where X is a number). See if each output leg is the same number. If it isn't see which leg the modem is currently plugged into. You want it plugged into the leg with least amount of loss.

Also check to be sure all the connectors are on snug and that there aren't any breaks, cuts, splits, (damage) to the cable lines, especially the one for the modem.
 
DOCSIS upgrades shouldn't effect the SB5100 if you have a port thats not used your losing signal from that. A 4 way splitter cuts db by 7.5 dbmv switch it out to a three way and you will boost the signal to ur modem by 2.0 dbmv a three way only dopr 5.5 so right there is a 2.0 gain. You can go 2way to two and put your modem on the first 2 way but you cause unecassary loss to your tv's it they are jus on standard cable your fine but if you have digital boxes this can cause a problem they to are just like modems they have to be on a homerun line.
 
The Comcast tech came yesterday and switched the main 4-way splitter with a 3-way splitter and replaced all of the connectors. The signal levels definitely improved after the change. I switched back to the old SB5100 modem and everything has been working fine.

Thanks for all the advice!
 
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