DSL problem

I was setting up my Grandma's DSL the other day, and was having trouble connecting to the Internet. Everything was hooked up properly, and the filters were on, etc. So I called Verizon, and the tech told me to try hooking up just the modem to a different phone line, just to see if the DSL led lights up solid. So I hooked up the modem to the jack in the living room, and of course it works. So the tech tells me that the other phone jack is bad.

The thing is, the other phone jack previously had a phone connected to it up until I disconnected it ten minutes before. The phone worked fine in that jack for years! I plugged the phone back into the jack and of course it worked. I pulled the jack apart and everything is wired properly.

The tech told me that I would have to replace that jack. I don't get it, the jack works.

Before FIOS, I had DSL form the same provider, and it didn't need any special type jack. Granted,her phone jack and wiring are probably 50+ years old, but then again so was the jack in the living room that worked with the DSL modem.

So what gives?

 

DSL utilizes aspects of the phone line not normally used by telephones (this is why you can use the telephone and surf the web at the same time), so a telephone may work and the DSL may not.
Call the phone company request a line test.

 

It does not matter what is the past stories.

The Modem worked on one jack and Not the other, then the service to the jack, or the jack it self is Not OK.

BTW, the phone line pumps relative high voltage low frequency signal. It is not uncommon that on a quirky line/jack the phone might work but the DSL would not.