Was having problems with my Optimimum Online cable service. I checked the cables as best I could, but still, intermitent service. The cable-guy came out with his monitoring box and determined that my splitter was the problem so he removed it from the loop and everything works great.
For those of you with a Surfboard SBV5120, I learned a quick way to find out if the signal is no good to the modem. Go to http://192.168.1.100 and put in id: admin password: motorola Then go to the Signal Strength tab.
Downstream Power Level should be -10 to 10 (0 is good)
Upstream Power Level should be around 46