Motorola SB6121 Constantly Restarts

Your signal levels are not very good. Could you describe how the cable wire gets from the pole to your cable modem? I predict at least 2 splitters, and one outside.

This probably isn't going to be as descriptive as you want but outside there are 3 wires that run to the Cox box.  2 wires appear to follow the power wire to the house and the other 1 cable has its own line directly to the pole.  Out of the Cox box there are 3 wires that run into the house (whoever wired them left them exposed on the outside of the house rather than running them underneath the house). 

Inside, the wire Cox used to was already in the house.  It runs about 12 feet and then goes to a splitter which does not actually split anything, since there is only one device (the modem) which is connected to the splitter by another 12 foot wire.

The signal levels you initially reported aren't good at all and likely what is causing your frequent reboots.  Eliminating the splitter that isn't being used would probaby help things out considerably.

Yea, I would first get rid of the splitter you don't need and see what that brings your signal levels and go from there.

I eliminated the splitter and now here is what I get:

Downstream Noise: 34dB

Downstream Power Level: -11 dBmV

Upstream Power Level: 51 dBmV

Is this good now?  So far since I moved the modem and eliminated the splitter, the modem hasn't reset itself in 2 hours.

Yea, its as I thought, I think some noise is leaking in on one of the splitters outside. Probably weather damage. Is this a multi occupant location? Sounds like you have more then one cable wire going to your house.

It is a single occupant stand alone house.  I have no idea why there are 3 wires coming into the COX box, I was surprised by that when I went out to look at the lines.

Oh, I'm not sure either then. 

It still looks to be some kind of signal problem, so if the wiring on the outside of the house is unusual, I would get that checked out first.

It's been a few days since the service call, so we just wanted to see how everything was going.

The signal history and modem log looks good since 9/28, so I think I already know, but we want to tie up loose ends. 

Im having the same exact issue that the OP is having. Can some one help me or do I need to see whats not being used on the splitter?

y I have a splitter running three lines. The modem cox set up, my Motorola sb6121 and the cable box. So there's not a line being used but now I'm wondering why I need the extra modem?

Im guessing  the extra modem is your phone modem. Turns the cable signal into phone signal. What is the modem's model number?

Also, is that just the splitter in that room, are are you looking at where the cable comes into the house?

The phone modems model # DPQ3212

The splitter is from the line outside the house.  The cable was set up like this from the previous tenet ants I'm assuming. It leads from outside the house and strategically wrapped into the house. 

Probably better for you to start your own thread since his/her issue seems to be localized, if not resolved. Post with some general details of the symptoms, signal levels, etc.