atcomsystems.ca/forum Forums General General Telephone & Systems Information dtmf?

Got stumped today.What would cause 4 ground start lines which are testing ok at the demarc, but when they go into the subs NEC PBX the lines are "picked up" but when you try to enter an extension,you hear the buttons beep but you aren't directed anywhere.You are defaulted to the operator who then connects you through.This is happening only on 4 lines out of more ground start lines going into the PBX.The NEC tech changed some cards but to no avail.Could DTMF be an issue?If so how is it tested?How or who can see it and adjust it?The switch is a DMS100.Any help is greatly appreciated.

Did you check polarity? Can you seize the lines from the PBX and call out?

No,didn't think to check polarity.Verizon's mantra is usually if dial tone is good at the demarc,you're done.At the demarc with the subs PBX inline,I was able to ANI the line and make a call with my test set.

You may be able to make a call from the Demarc, but your butt set doesn't care about polarity the PBX does. Not saying that's the problem but I'd sure verify it before going any further. You can select a trunk from the PBX console can't you? Do it from there and see if you can call out. My moneys on reversed polarity.

This is the way we checked for rev. polarity when I worked on the Dimension product line at PT&T.
monitor the line at the demark with your test set,using a wire attached to ground touch the side of the bp you believe to be the ring of the line, if you hear DT the line is not reversed. IF not touch the other side; if you hear DT that is the ring side.
if the line is correct at the demark continue testing all the way thru any cross connects all the way to the pbx.
This works because if you are going off hook with your test set you are placing a short on the line and the ground is bring up the co circuit, how ever if you are monitoring the line you are only grounding 1 wire towards the co and are able to determine which is the ring side.

TommyB52:

When you make test calls with your butt set, did you have to ground one side of the line to draw dial tone? If not, thenVerizon doesn't have the trunks set for ground start.

I'd tend to think that if polarity was reversed, these trunks would be ringing in constantly.

My bet is that Verizon is using some form of pair gain equipment on these trunks that has not been configured properly. They may have done such a conversion without anyone's knowledge.

The old NEC NEAX2400 had to have proper grounding for GS trunks to work. There was also a loop plug on one side of each PIM that needed to be in place when you used only one power supply per PIM. I have seen them work great while you were programming with a terminal that was grounded and the trunks would quit when you removed the programming terminal.

I had to ground the tip side to get Dial tone and the lines are on copper not pair gain.The PBX was the vendor's responsibility to maintain so I couldn't physically change a port, the vendor had to do it.I grounded the side that didn't have 48 volts. If I go back there I'll check the polarity.Am I wrong but I thought on a ground start loop, with the butt set on,you were supposed to ground the tip side(without the 48 volts) not the ring.I have 15 years as a splicer but ground starts,DIDs,p-sets are a little new to me.Thanks for all the info so far.

If you have a butt set across the pair, and switched ON, then grounding either side will ground the ring side, because they are connected together via the buttset. This does not accomplish anything.

To determine accurately which is the ring side, just put your KS meter from ground to both sides, one side at a time. The ring will have -48 volts on it, just like the ring side of a loop-start line. The tip side will be open, with a healthy kick back to the CO. It will look like a line that has an open tip at the frame.

Watching the tip side with the meter, ground the ring with a piece of wire. The CO will see the ground, and cut-through the tip at the CO equipment.

Are you using Ground Start Trunks for Incoming? When you say the lines are "picked up" but you aren't directed anywhere - are you trying to call in and reach an extension?

I ask this because in all the years I worked on PBXs, Incoming trunks were either:
A) DIDs, which are loop start or
B) E&M which are loop start (well they're not Ground Start) or
C) Analog ICTs, which were also Loop Start

I'm sure that Incoming Trunks could be Ground Start, but I never saw one. Maybe these are supposed to be Out Going Trunks?

If I'm misunderstanding you then please correct me. If these are OGTs and you can't dial out then I would agree with the other guys and say - definitely a polarity reversal.

Try a quick and dirty (and easy) test. Reverse the polarity of the line, reconnect it and test it.


Sam