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telephony question

Discussion in 'General Electronics Discussion' started by jdw1, Oct 10, 2012.

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  1. jdw1


    Oct 10, 2012
    I have built a 19-station intercom system for my community theatre, and Im having trouble with the circuit.

    I used an Elgin EAK-4 key, coupled with a Tel-Tone T-19 switcher. I managed to locate the original T19 wiring guide and followed it explicitly. THis routes through a series of Western Electric 2500 touch-tone telephones. The EAk-4 and the T-19 were given to me free of charge. The phones were procured from a thrift store. The circuit is encased in a plywood box with a 3" exhaust fan.

    On intial testing, the system appears to operate perfectly - all phones can talk back and forth on signal and each unit can "ring" any other unit in the system. However, once all units are connected, some cannot send or receive rings. So far, in all tests, there is a time difference of 30 minutes to an hour between first test (two units) and final test (10 units).

    I was getting frustrated with this symptom when it occured to me that I have a second that I had heretofore ignored: after 1/2 hour or so, the signal volume on all units drops to a point such that the voice on the other end of the line is barely audible. It belatedly occured to me that both symptoms could easily share a single cause - voltage drop.

    My first thought was a heat related problem, so I removed the cover from the box, turn the unit off, and waited 1/2 hour. No better. Next, I considered the ground; all grounds are made to the chassis of the EAK-4 using 20-gauge wire. So, I used a 12 gauge cheater to ground the circuit to a 4'x4'x9" steel junction box on the wall. Again, no improvement.

    Now, I'm thinking there are two remaining possibilities - (1) I've screwed up something in the 124 connections used in building this circuit, or (2) there was a really good reason why these parts were free.

  2. shrtrnd


    Jan 15, 2010
    Just trivia.
    I got a bunch of phones from an office that replaced their phone system with a
    new one. Took the phones home and tested them out. They had ALL be modified
    by the original contractor, to be wired to their original telephone system equipment.
    Before you go rechecking all your wiring, open one of the phones, and see how
    they're wired.
  3. jdw1


    Oct 10, 2012
    Thanks. I'll look into that.

    Any other thoughts?

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    Have you measured the PSU voltages? Did you measure the loop voltage,.. on and off hook?

  5. jdw1


    Oct 10, 2012
    No, I figured that was going to be the next step. I plan to do so ASAP, but, for now, my job keeps getting in the way! LOL.

    Thanks. Any other suggestions will be greatly appreciated.
  6. Frank Bittner

    Frank Bittner

    Oct 11, 2012
    What exactly do you mean "when all units are connected some cannot send or receive rings?
  7. donkey


    Feb 26, 2011
    could this be either too many handsets or the powersupply needing to be upgraded for more amps?
  8. jdw1


    Oct 10, 2012
    When I test the unit with multiple telephones connected, sometimes, when dialing the connection number for one station from another station, the switch makes an aubidle click, but the dialed station does not ring. However, when I go to another station (frequently the one just tested) and dial either the original station or a third station in the system, the dialed station rings as designed. Every time I reset the system, which stations dial properly and which don't seems to change randomly.
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