TDM410P does not pickup telco line

I have 5 Freepbx 2.10 Systems, each system has two or more Telco lines, 4 systems work great, 1 system has an issue with both the Telco lines at site.
The issue is when an external calls in, the external user hears the telco ringing, internally asterisk CLI shows the FXO line ringing, internal users phones ring, when they try to answer, call is terminate for internal user, phone do this a few times until eventually call goes to the IVR. During this time all the external user hears is the Telco ringing.
Internal users cannot make out going calls, on FXO
I replaced the TDM410P card 3 times, swapped FXO modules until finally the system worked for a few days. However the issue is now back.
When I called the reseller of the card they said use elastic as it is most likely a driver issue.
I have updated the system, all the modules are the latest.

Any other ideas?

I would bet you that you have a bad connection on the line going to the card. The ring detector is sensitive enough to pick up 1/2 the ring waveform. When you come off hook DAHDI detects no voltage so it hangs up the call.

So I started from scratch, rebuilt a new system, new TDM410P, different machine, test in shop worked. Brought it to the site, Dahdi 1 works, Dahdi 3 does not work, Dahdi 4 works.

Using the same Telco on each Dahdi
Dahdi 1, idle 53V, on Hook 10.5V
Dahdi 3, idle 53V, on Hook 53 V

I tried changing the FXO to loopstart, no difference, running fxotune no difference is there any setting for line impedance?

Did you see my note? The wiring is bad.

Thanks I did get the note, I failed to mention that I also reran the telco lines back to the demarc and re terminated both the lines. I realize the lines are flakey, my question are there any settings for dahdi that I can set to compensate for the lines.

I don’t think you can take it that far down. If this is the US telco has to fix it, that is below tariff voltage.

I have also seen this on the DOCSIS telephone adapters the cable companies use. I just push the tech to swap it out.

Ok, I figured as much I have a mediatrix box so I will install that until we can get the Telco company to take a look.
Thanks for your help

We installed line current limiters from As far as I can tell from research on th net Telco lines are with in the specs. However the line modules from Nicherons cannot handle the upper limit of the Telco. Basically what was happening was when we had an incoming call the line module would burn out. Nicherons did eventually replace the modules at a cost to us.


Thanks for posting your fix! I have an issue at one client and suspect the analog lines themselves but was not sure how to test/prove it.