Elmeg CS400xt ISDN telephone

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  • stenio
    Member
    • Sep 2023
    • 10
    • Italy
    #1

    Elmeg CS400xt ISDN telephone

    Hello,

    I need some advice with this telephone that suddenly stopped working: nothing showing on the display, no dial tone and no leds.

    The telephone is powered with the ISDN RJ45 cable.
    I tried to plug another phone on the same cable and it works perfectly, so the problem is not the cable nor the PBX.

    I performed a visual inspection but I did not see anything strange.

    No shorts on the electrolytic caps.

    I measured 34V between some pins of the connector near the S0 RJ45 connector.

    I also tried to see if some components are getting hot using a thermal camera, but everything is cool.

    Maybe I should try with voltage injection?
    What test can I do with the board disconnected from the PCB?

    What do you think?

    Thanks,
    Stenio
    Attached Files
    Tags: None
    • CapLeaker
      Leaking Member
      • Dec 2014
      • 7976
      • Canada
      #2
      Re: Elmeg CS400xt ISDN telephone

      Could be a voltage regulator problem, could be bad chrystals (there are 2), bad capacitors, a shorted diode, bent pins on the phone jack, a bad esd device or a bad flash chip. Anyone of these in the right spot will make the phone not work. Poke around and see if you find power around there, check with an oscilloscope if the crystals are swinging. You can check for data transfer on the D0 line (the phone gotta boot). Tons of stuff to do. Don’t be too shy, go and poke around in there!

        Comment

        • stenio
          Member
          • Sep 2023
          • 10
          • Italy
          #3
          Re: Elmeg CS400xt ISDN telephone

          I am struggling to find how the phone is powered through the S0 port.
          Four of the RJ45 pins are connected to a header which is connected to an IC called VOGT T4 503 06 047 40 and then to IC VOGT T4 5031650300. Unfortunately I was unable to find a datasheet of these chips.
          Two pins of the socket seems unconnected.
          The first and the last one are connected to two vias but I can’t find to where they are connected.

          Do you have any ideas of the porpoise of the two ICs?

          I wonder if the S0 bus follows some pinout standard.

          Thanks,
          Stenio
          Attached Files
          Last edited by stenio; 09-23-2023, 07:46 AM.

            Comment

            • stenio
              Member
              • Sep 2023
              • 10
              • Italy
              #4
              Re: Elmeg CS400xt ISDN telephone

              I've found the datasheet of the IC VOGT T4 503 16 503 00:
              it's an interface transformer. As for the VOGT T4 503 06 047 40 I think it's choke.

              Furthermore the power should come in from pins 3/6 or 4/5 of the RJ45 socket.

              Let's see where I go from here.

                Comment

                • stenio
                  Member
                  • Sep 2023
                  • 10
                  • Italy
                  #5
                  Re: Elmeg CS400xt ISDN telephone

                  I fixed it! It was a broken via on the phantom power circuit.

                    Comment

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