Make a Tester Build yourself a simple phone line tester. ~ Total Cost $35.00
Attach a D'Arsonval movement VOM to the back of a fax handset. wire the input=female RJ11 red & green wires to a DPDT switch (to reverse the polarity), then to the VOM/handset. This is not terribly high tech, but you can identify a really bad, out of specs phone line.
Plug the phone cord into your new tester. Check these voltages:
On Hook: -48 VDC (-42.5 to -56.5 VDC), 90 VAC
Off Hook: -10 VDC (-8 to -12 VDC), 8 VAC
Ringing: peak 125 VAC (110 to 137 VAC)
The polarity only matters so that your meter will deflect the correct direction. All modern faxes correct their own polarity.
If the line is out of specs, check the same voltages at the demarc (where the phone line comes into the building). If voltages are still out of specs, its the local telephone provider. If its OK at the demarc, you can be sure its the PBx.
It sounds complicated, but with the tester and a little practice you'll be out of there in 10 minutes with proof it's not your machine. That can be hard to come by.
You'll spend $200 or more for a commercial tester with these same features.
Phone Line Tester.JPG
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