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PBX Music On Hold

Discussion in 'Electronic Design' started by Dave, Apr 24, 2007.

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  1. Dave

    Dave Guest

    I bought a cheap telephone PBX for my small business and much to my
    dismay it has horrible music that plays while the caller is put on
    hold. It's like midi Fur Elise or something. There seems to be no
    way to change it in the normal settings.

    I popped off the top of it just to have a look inside and I noticed
    all the IC's are socket mount big old things and it's a pretty simple
    looking device. I'm just wondering if there might be something I can
    do to disconnect the music. Any ideas about what IC might be the
    culprit and what I might be able to do about it?

    The IC's:

    AT89S51 - 8-bit Microcontroller with 4K Bytes In-System Programmable
    AT24CO4PC - 4Kbit, 2-Wire Bus Serial EEPROM
    DLT 8816 - This chip has a scratched top and looks like it is a re-
    badged processor, same form as the AT89S51
    CS9370DGP - DTMF demodulator (there are 3 of these)
    HEF40106BP - Hex inverting Schmitt trigger
    PS2501-2 - High isolation voltage single transistor type multi photo
    NEC 2501 - probably older version of the PS2501
    HD74HC244P - Octal Buffers/Line Drivers/Line Receivers with Non-
    inverted 3-state outputs
    M402100BP - Crosspoint Switch Circuit - Dual 4x4 Crosspoint Switch

    The first 3 are my prime suspects. Here's a pic of the board:

  2. Look for a to-92 package (plastic 3-legged transistor style) with UM66T19x
    on it. Pin 3 would be the output pin.
  3. Joe G

    Joe G Guest

    There are some TO-92 transistor like Melody Generators that have been
    used before in PABX's.

    Like these

  4. Nico Coesel

    Nico Coesel Guest

    You can probably find the music signal on the crosspoint switch with
    an oscilloscope or an earphone. You can use a 1k Ohm resistor and a
    1uf capacitors in series to attach a CD or MP3 player.

    8816 sounds familiar though. I think this is a remake of a Mitel chip:

    It could be a 8x16 matrix analog switch. Makes sense because a 4x4
    crosspoint switch is not enough for a PABX with 8 lines.
  5. Ross Herbert

    Ross Herbert Guest

    I assume that the user manual (if you have one) doesn't give any
    information on whether or not the MOH function can be disabled by an

    Other than that, it might be best to direct your query to the
    manufacturer in China
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