Stumped? LOL

First, have you taken measurements on the trunks yet? Voltage, current and readings between ground and tip and then ring. The voltages you should see on a normal POTS central office trunk are -48 VDC between tip and ring when idle. The voltage should be, somewhere around -7 VDC off hook. The current should be in the range of between 25 to 35 ma. Check the voltage during a call and then stay on the line with your VOM as the call is terminated. What is the condition after the call is terminated? Check all these measurements with the trunk card installed and then remove the trunk card and make the same measurements with your butt set.

If this condition just happened, I would look at telco changes. Did they migrate from copper to fiber or maybe a T-1 with a channel bank? The SX-50 is forgiving of a lot of abuse, but if you have a high AC influence on the circuit, the problem you describe will occur. We service a motel in the sticks with a long line run from the CO and, from time to time, we see this exact same condition. A call to the telco gets another patch job and the trunks work for another 6 months.

Look for AC from ground to tip and ground to ring after the call is terminated. There should be none. Also, check your local system ground and the telco cable ground. There should be zero ohms or a very low ohms reading between your system ground and the telco cable bond ground.

Stumped? No. Lack of info? Yes.

Rcaman

Americom, Inc.
Where The Art And Science Of Communications Meet