Hi guys, I've been experiencing a very strange issue with my Digium Card TDM400 as of this week. It has two FXS and two FXO. The FXO modules (both of them) never goes on-hook after hanging up in Asterisk. It had worked perfectly well for over four years. I put an ammeter in series with the line and the card, and immediately after plugging the connector to the card, I got 26mA in the circuit and a dial tone from the carrier, where it should be zero amper (on-hook state). If a Dial() something, it works perfectly. I can Hangup() the call, freeing the channel in Asterisk, but the hardware keeps off-hook forever, locking the line. If I Dial() again, Asterisk opens the line, sends the DTMFs normally, but it doesn't work since the carrier thinks I'm still holding the first call. It behaves exactly the same way with another analog line. If I plug either of the lines and my other Digium card (TDM2400), it works ok. The same with my Brazilian DigiVoice FXO card. Ok, you all might say: your card is damaged, throw it away. Ok, I could do it, but now comes the funny part: If I put an DSL filter in series with the line and the card, IT WORKS PERFECTLY!!! The filter imposes 25 ohms over the circuit. Maybe that's causing the card to work. When I put the filter and the ammeter in series, I get zero amper when on-hook and 26 mA when off-hook, that's the expected behaviour. I'm not an expert in electricity, so I really don't know why the card is behaving that way. What does that resistance make for the card to start working ok? I know the DSL filter isn't only a resistor. Maybe it has another electrical component that's helping more than the resistor. Just a guess. Tomorrow I'll buy a 30-ohm resistor, take the DSL filter off, and test the card only with the resistor, to check it out. In order to isolate the problem even more, I plugged the FXO port in one FXS port. Immediately after plugging it, Asterisk announced at the console that someone went off-hook at the FXS port. So, it's not really a carrier issue. The FXS port is perfectly -48V on-hook, and about 20 mA in the circuit when off-hook, closer than the carrier to the standard values. Any clue is welcome. -- MARLON DUTRA Propus GnuPG ID: 0x3E2060AC pgp.mit.edu http://www.propus.com.br/ http://hackers.propus.com.br/~marlon/
You need to replace the FXO module Was there ever any sort of protection installed for the module? Not what your carrier provides, that protects their equipment, but any secondary protection? These modules are easily damaged. I know of one connected to a very old SXS switch that damages from a small inductive kick when it opens ( goes on hook ) John Novack Marlon Dutra wrote:> Hi guys, > > I've been experiencing a very strange issue with my Digium Card TDM400 > as of this week. It has two FXS and two FXO. > > The FXO modules (both of them) never goes on-hook after hanging up in > Asterisk. It had worked perfectly well for over four years. > > I put an ammeter in series with the line and the card, and immediately > after plugging the connector to the card, I got 26mA in the circuit and > a dial tone from the carrier, where it should be zero amper (on-hook > state). If a Dial() something, it works perfectly. I can Hangup() the > call, freeing the channel in Asterisk, but the hardware keeps off-hook > forever, locking the line. If I Dial() again, Asterisk opens the line, > sends the DTMFs normally, but it doesn't work since the carrier thinks > I'm still holding the first call. > > It behaves exactly the same way with another analog line. If I plug > either of the lines and my other Digium card (TDM2400), it works ok. The > same with my Brazilian DigiVoice FXO card. > > Ok, you all might say: your card is damaged, throw it away. Ok, I could > do it, but now comes the funny part: > > If I put an DSL filter in series with the line and the card, IT WORKS > PERFECTLY!!! The filter imposes 25 ohms over the circuit. Maybe that's > causing the card to work. When I put the filter and the ammeter in > series, I get zero amper when on-hook and 26 mA when off-hook, that's > the expected behaviour. > > I'm not an expert in electricity, so I really don't know why the card is > behaving that way. What does that resistance make for the card to start > working ok? I know the DSL filter isn't only a resistor. Maybe it has > another electrical component that's helping more than the resistor. Just > a guess. > > Tomorrow I'll buy a 30-ohm resistor, take the DSL filter off, and test > the card only with the resistor, to check it out. > > In order to isolate the problem even more, I plugged the FXO port in one > FXS port. Immediately after plugging it, Asterisk announced at the > console that someone went off-hook at the FXS port. So, it's not really > a carrier issue. The FXS port is perfectly -48V on-hook, and about > 20 mA in the circuit when off-hook, closer than the carrier to the > standard values. > > Any clue is welcome. > >-- Dog is my co-pilot
On Fri, Apr 11, 2008 at 11:43:19PM -0300, Marlon Dutra wrote:> If I put an DSL filter in series with the line and the card, IT WORKS > PERFECTLY!!! The filter imposes 25 ohms over the circuit. Maybe that's > causing the card to work. When I put the filter and the ammeter in > series, I get zero amper when on-hook and 26 mA when off-hook, that's > the expected behaviour.It's possible the 'line relay' on that card is not a physical relay, but electronic, and that its sensitive to too much loop current -- and the DSL filter drops the current far enough for that 'relay' not to pull in spuriously. Telecom guy Mike Sandman has a paper on loop current on his website: http://sandman.com/loopcur.html and, come to that, lots of *really* cool stuff for sale as well; if you've never looked at his site, do. Cheers, -- jra -- Jay R. Ashworth Baylink jra at baylink.com Designer The Things I Think RFC 2100 Ashworth & Associates http://baylink.pitas.com '87 e24 St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274 Those who cast the vote decide nothing. Those who count the vote decide everything. -- (Joseph Stalin)