Do we need a digital modem for Comcast cable phone service? 1

[eatatparkys]

We recently installed service for Comcast digital voice phone service. Now our US Robotics 56K Fax Modem Model #5686E seems to be humming and buzzing. (We use it to process credit cards as a dial-up backup for our Micros 3700 POS system if the internet goes down.) There are no LED lights lit on the modem. Is there a fix or do we have to get a new modem?

 

[eatatparkys]

I should add that Comcast has confirmed that their phone service comes in as digital and then it's converted to analog so it wouldn't seem that would be the problem with the modem.

 

[macphoneguy]

I'm thinking a couple things, first I would query the modem, from a PC, to see if the modem responds, (windows control panel/modems) if it doesn't then thats a problem, either with the serial cable or the power to the modem, as to the Hum/hiss I would likely want to plug a regular analog phone into the jack on the modem, if you make a call and it is not good/clear, then I would confirm it is good at the comcast unit, if it is good there, then you have some wiring issue of some kind between there and the modem, which can be any number of things such as poorly terminated wire/wire too close to florsent lights or AC,
or poor grounds inducing noise