Com Key 416 "4A" Communication System
-------------------------------------
                 
                   A Com Key 416 Rotary "Satellite" Station
                                        Model 981


                                 * * *     * * *     * * *

    NOTE: The following information is available from http://seriss.com/erco/comkey416/.
    The info was compiled from several sources by Greg Ercolano, and is provided AS IS.
    Not responsible for errors. For authoritative information on Com Key 416 systems,
    refer to the original Bell System documentation. The following information may be
    republished in part or in whole, provided 1) this attribution/disclaimer remain 
    intact and un-edited, and 2) the above URL be provided.

                                 * * *     * * *     * * *

    The Com Key 416 ("4A Communication System") was released by AT&T circa 1975
    as an alternative to the older 1A2 phone systems. The Com Key system
    has all the control functions (normally found in separate KSU boxes) in
    the phone sets themselves.  As such, the Com Key 416 systems are referred
    to as "KSU-less" systems.

    Com Key 416 systems consist of at least one "Primary" set, and one or more
    "Satellite" sets. The Primary sets are slightly larger than the Satellite
    sets because they house control circuitry common to the rest of the system.
    The Primary sets also have an AC cord, to supply power to the control
    circuitry, and the power supply that powers the Satellite sets over the
    standard 25 pair cables.  Both Primary and Satellite station sets have
    Amphenol-type 25 pair (50 pin) male ended cables (similar to the modern
    "RJ-21" style connectors and cabling used for networking)

    Several features that were complicated options on the older 1A2 systems
    come standard with Com Key 416 systems, such as programmable ringing,
    DSS, voice announcements, conferencing, and intercom.


Com Key 416 Features
-------------------

    Some of the notable features of this system:

        * Master set has all the control circuitry built in; no KSU box needed.

        * Call Holding (put a call on hold, so one can either answer another
          call, or move to another phone to take the call there, or use the
          intercom/page to tell someone else to pick up the call..)

        * 2 path intercom with voice or tone signaling:

                1) Pick up handset
                2) Select an idle ICM button
                3) Press one of the white DSS buttons (center of phone)
                   to signal one of the other stations                  

        * Multiline conferencing (two or more phone lines can be conferenced
          by jamming down two or more of the line buttons simultaneously)

        * Built in loud speaker can be enabled by toggling the SPKR button on
          (top button on row of line buttons) allowing others in the room
          to hear both sides of the conversation.

        * Auto-release of line buttons (ABR - Auto Button Release).
          As soon as the handset is returned, any line buttons down
          will pop up.  This is to prevent accidentally lifting the receiver 
          on an active line.

        * Recall: similar to 'flash'; a way to flash the line without
          loosing the call to access PBX/CO features.

        * Ringing is completely programmable: each set can ring
          on all lines, one line, or no lines.

        * Privacy release: a way to allow other stations to pick up
          the same line if the station is programmed for 'privacy'


Com Key 416 Technical Info
-------------------

    The systems are somewhat "user programmable"; switches under the hinged
    faceplate on the DSS keys can be set by the user to control which CO lines
    cause the phone to ring, and also sets the phone's DSS key number.  This,
    as opposed to the older 1A2 systems where a telco field engineer would
    have to configure such features with extra hardware and punch block
    configurations.

    A notable internal feature of the Com Key 416 phones is their modular
    design; just about everything inside the phone is a 'module' that can be
    removed and replaced separately, many can be removed without tools. All
    modules are connected to an interconnect board (located under the DSS
    keys) with easy to remove connectors, which simplifies servicing and
    debugging.

    The interconnect board also houses user-modifiable jumpers to access
    various factory features that can be changed when add-on hardware kits
    are installed or removed.

    To access the interconnect board, one can pry up the metal face plate,
    and remove the snap-in DSS key module under which the interconnect board
    is located. Both the DSS key module and dial pad/rotary dial modules can
    be completely removed without tools by novel 'snap in' locks.

    Com Key 416 systems required at least one "Primary" or 'master' phone
    which can manage up to 2 Central Office (CO) lines, and provides a single
    intercom path. Off this master phone, multiple "Satellite" phones can be
    connected by standard 25 pair cables.

    A second "Primary" phone can be added to the system to add two more CO
    lines for a total of four lines and two intercom paths. Satellite phones
    also support a single 'private line' each.

    The "Primary" sets house the line control circuits that manage the functions
    common to all the "Satellite" phones, and have an AC power cord that require
    a grounded outlet. The Satellite phones are dependent on the "Primary" sets 
    for most of the system's features and power.

    The Primary sets are physically larger than the Satellite sets; it has a
    larger base which houses the AC power supply and numerous control circuits
    and relays not found in the Satellite phones.  The Satellite phones are
    smaller and do not need any AC power; they get their power from the Primary
    sets over the 25 pair cables.

    Like 1A2 systems, on power failure one can still dial out, and calls in
    progress over the CO lines are unaffected. This is due to the fact the
    mechanical line buttons physically connect you to the CO lines, and these
    connections are unaffected by a power failure.  Only the visual (lamps)
    and audible (ringing) signaling features would be disabled, as well as
    intercom, hold, and other such features.  This means incoming calls will
    not ring (unless separate ringers are provided that run off the CO's ring
    current) Options are available for power-fail ringing, which would
    automatically be switched in when the power fails, and switched out when
    power is restored.

    A typical system involves at least a Primary set, zero or more Satellite
    sets, and a 91A or 91B "connecting block" which interfaces the Primary
    set to the CO lines, and any number of optional Satellite sets (see
    "Technical Limits" below). 
    
    

    The 91B connecting block is a simple circuit board with a single RJ-11
    connector for the two CO lines. It also has two (50) pin amphenol
    style connectors; the Female connector is intended to run to the male
    end of the Primary set's station cable, and a Male connector intended
    to mate with a female "single ended" cable that runs to the back board
    66 blocks, which should in turn distribute to other female ended runs
    back to all the satellites, creating a 'star' or 'home run' configuration.


Wiring
------
    Setting up a phone system was just a matter of attaching the CO lines
    to the "91B" block, a 7 foot 25 pair cable between the 91B and the
    Primary station, and a 25 pair from the 91B out to the Satellite station(s).
    
    If you don't have a 91A or 91B connection block, you can attach to the
    telco lines directly to the primary set:
    Connect CO's Line#1 T/R pair to pins 24+49 (brn/vio + vio/brn) respectively.
    Connect CO's Line#2 T/R pair to pins 25+50 (slt-vio + vio-slt) respectively.
    If the primary set is internally configured for Line1&2, the two CO lines
    will appear on the first two buttons above the Hold key. 
    If the primary set is internally configured for Line3&4, the two CO lines
    will appear on the 3rd and 4th buttons above the Hold key.
    (WARNING: Do NOT wire "1A2 style" to 1+26: that's wrong for Com Key.)

    Wiring to the Satellite phones can either be a "Home Run" (ie. "Star") wiring,
    or "Bridged" (ie. "Daisy Chained"), or combos of both.  "Bridged" configuations
    are easiest to configure for the novice, and use the least amount of cable.
    Such configurations are made possible by "bridging adaptors"; "Y" splitters
    for the 50 pin amphenols, so that a single 50 pin connector can be split
    into two; one for the phone, and one for the continuing run. (BSP III 
    518-450-106 2.10)

    All station set cables are male ended, and should mate with a female
    cable that runs to the back board or 91B block.
                          Typical Amphenol Male / Female cables mated


Programming Features
----------------
    There are two places two "program" the phone:

        A) The cover between the top and bottom rows of DSS buttons
           covers the switches that set the phone's DSS number
           and ring programming

        B) Under the metal face plate (you have to pry it up),
           you can remove the entire DSS button pad by snapping it out,
           revealing an jumper box for various other features of the phone.

    See below for details.

    Some features can be programmed at the 66 blocks, but the intention
    is for most features to be programmed in the phone sets.

    Some optional features (paging, music on hold..) involve separate hardware.


Technical Limits
----------------
    The recommended technical limits of the system are 2 Primary sets, 
    14 satellite sets, two intercom paths, 10 DSS paths, and 4 CO lines. 
    Each primary can support up to 7 satellite sets.  Since the Primary sets
    are phones too, a total of 16 phone sets can be used.  (BSP III 518-450-106
    2.08 and 518-450-105 2.01)  There is an absolute maximum cabling limit
    of 2000 feet total. With a maximum of 16 stations, the limit of cable
    length between satellites to both primary stations is 400 feet. (BSP III
    518-450-106 3.15)

Com Key 416 -- Bell System Model Numbers
----------------------------------------
   There are at least two series of Com Key 416 phones; 
   the 830/2830 series (BSP III 518-450-105), and the newer, more 
   common 980/2980 series (BSP III 518-450-106).

   The most common to encounter are the 980/2980 series, which 
   can be identified by having the green LED lamps mounted to the 
   left side of the line buttons, as opposed to the lamps being
   part of the buttons.

   Both series are intercompatible with each other, but the newer
   series supplied more features.

   830/2830 Series
   ---------------
   This is the older 830/2830 series, which have the lamps mounted 
   inside the line/intercom buttons.

        ******* Rotary Dial ******        ****** Touch-Tone Dial *****

        Model     Description             Model      Description
        --------  -------------------     ---------  --------------------
        836AM-50  "Primary" Station       2836AM-50  "Primary" Station
        837AM-50  "Satellite" Station     2837AM-50  "Satellite" Station

   The model numbers were often followed by letter/number codes
   to define particular features, such as wall mounting vs. desk sets.
   (Reference: BSP III 518-450-105 "Ordering Guide")

   980/2980 Series
   ---------------
   This later series, which seems to be more commonly encountered,
   has the lamps to the left of the buttons. 
   
   This series is compatible and interchangeable with the older
   830/2830 series.

        ******* Rotary Dial ******     ****** Touch-Tone Dial *****

        Model   Description                 Model    Description
        ------  -------------------         -------  --------------------
        981A01  "Primary" Desk Station      2981A01  "Primary" Desk Station
        981A02  "Satellite" Desk Station    2981A02  "Satellite" Desk Station
        983A03  "Satellite" Desk with BIS   2983A03  "Satellite" Desk with BIS
        983A02  "Satellite" Desk with HFAI  2983A02  "Satellite" Desk with HFAI

   (Reference: BSP III 518-450-106 2.10)

Com Key 416 Buttons
-------------------
    The DSS keys, from left-to-right, top-to-bottom, the keys are:

                       _____ _____ _____ _____ _____ 
                      |  1  |  3  |  5  |  7  |  9  |
                      |_____|_____|_____|_____|_____|

                       _____ _____ _____ _____ _____ 
                      |  2  |  4  |  6  |  8  |  10 |
                      |_____|_____|_____|_____|_____|


    Between the two rows of buttons is a pop-up cover that contains
    white switches that set how the phone rings, and the phone's
    DSS code:


         _      _         1    3    5    7    9             _      _  
        |_|    |_|     _____________________________       | |    | | 
      1 | |  2 | |    |__|__________________________|    3 |_|  4 |_| 
        |_|    |_|    off   2    4    6    8    10         |_|    |_| 

      \___________/   \_____________________________/    \___________/
            |                         |                        |
    "Common Audible"              DSS Intercom          "Common Audible"
      Switches for                Code Selector           Switches for
      Line 1 + 2                                          Line 3 + 4
     (shown "on")                                        (shown "off")

    The "Common Audible" switches select whether this phone should
    ring when Line 1/2/3/4 are ringing. eg. if switches "1" and "2"
    are turned on, and "3" and "4" are off, then the phone will only
    ring when a call comes into Line 1 or Line 2. The phone will be
    silent when calls arrive on Line 3 or Line 4.

    Here's an MP3 of a Com Key 416's ring: comkey-416-ring.mp3

    The "DSS Intercom Code Selector" sets which DSS key this phone
    will respond to. If set to "off", the phone will not be on anyone's
    DSS keys. When set to eg. "7", this phone will respond when 
    anyone presses and holds DSS button #7 and begins speaking;
    their voice will be transmitted through the loud speaker in the
    phone.

    The vertical row of line buttons at the right of the phone are,
    from top to bottom:

        Spkr    - Speaker button
        Prv Rls - "Privacy Release"
        ICM-2   - Intercom #2
        ICM-1   - Intercom #1
        Personal Line - unused, unless this option is provided
        Line 4
        Line 3
        Line 2
        Line 1
        Hold

   These are mechanical buttons; when Hold is pressed and released, or
   when the handset is placed on hook, any Line buttons or ICM buttons
   that were down are released. It is possible to press and hold several
   Line buttons down together to form a conference call. Similarly, both
   ICM buttons can be held down together to conference two intercom calls
   together. You can NOT conference between ICM and Line buttons; the
   mechanics of the buttons prevent this. Hold and Prv Rls are both momentary
   switches, Spkr is a toggle button.

   At the lower-left, the "R" button is a momentary button that flashes the hook,
   as a way of notifying the PBX operator.

   At the lower-right, a volume knob numbered 1 through 10 controls the speaker
   volume, when the SPKR button is locked down.

Com Key 416 Pin Out
-------------------

    The pinouts for the Primary and Satellite sets are similar, except for
    pins 23-25 and 48-50.

                                * * *  P R I M A R Y   S E T  * * *

                         BSP                                          BSP
           Pin  Color    Code   Description             Pin  Color    Code   Description
        _  ---  -------  -----  -------------------     ---  -------  -----  -------------  _
       |     1  blu-wht  R(1)   "Ring"                   26  wht-blu  T(1)   "Tip"           |
LINE 1 |     2  orn-wht  CA1    Common Audible 1         27  wht-orn  A(1)   A lead          |
       |_    3  grn-wht  LP(1)  Lamp                     28  wht-grn  LC(1)  Lamp Common     | 
        _                                                                                    |
       |     4  brn-wht  R(2)   "Ring"                   29  wht-brn  T(2)   "Tip"           |   Com Key
LINE 2 |     5  slt-wht  CA2    Common Audible 2         30  wht-slt  A(2)   A lead          |  "Internal"
       |_    6  blu-red  LP(2)  Lamp                     31  red-blu  LC(2)  Lamp Common     | signal paths
        _                                                                                    | for line 1-4
       |     7  orn-red  R(3)   "Ring"                   32  red-orn  T(3)   "Tip"           |
LINE 3 |     8  grn-red  CA3    Common Audible 3         33  red-grn  A(3)   A lead          |
       |_    9  brn-red  LP(3)  Lamp                     34  red-brn  LC(3)  Lamp Common     |
        _                                                                                    |
       |    10  slt-red  R(4)   "Ring"                   35  red-slt  T(4)   "Tip"           |
LINE 4 |    11  blu-blk  CA4    Common Audible 4         36  blk-blu  A(4)   A lead          |
       |_   12  orn-blk  LP(4)  Lamp                     37  blk-orn  LC(4)  Lamp Common    _|

            13  grn-blk  ICR1   Intercom#1 "Ring"        38  blk-grn  ICT1   Intercom#1 "Tip"
            14  brn-blk  DSS1   DSS Button #1            39  blk-brn  DSS2   DSS Button #2
            15  slt-blk  LCI1   Lamp Common Intercom#1   40  blk-slt  LPI1   Lamp Intercom #1

            16  blu-yel  ICR2   Intercom#2 "Ring"        41  yel-blu  ICT2   Intercom#2 "Tip"
            17  orn-yel  DSS3   DSS Button #3            42  yel-orn  DSS4   DSS Button #4
            18  grn-yel  LCI2   Lamp Common Intercom#2   43  yel-grn  LPI2   Lamp Intercom #2

            19  brn-yel  DSS6   DSS Button #6            44  yel-brn  DSS6   DSS Button #6
            20  slt-yel  COM    Power Supply Common      45  yel-slt  +V     Power Supply +
            21  blu-vio  DSS7   DSS Button #7            46  vio-blu  DSS8   DSS Button #8

            22  orn-vio  DSS9   DSS Button #9            47  vio-orn  DSS10  DSS Button #10
         _  23  grn-vio  MOH    Music On Hold            48  vio-grn  MOH    Music On Hold           _
CONNECT |   24  brn-vio  R1/R3  CO "Ring" line 1 (or 3)  49  vio-brn  T1/T3  CO "Tip" line 1 (or 3)   | CONNECT
 TO CO  |_  25  slt-vio  R2/R4  CO "Ring" line 2 (or 4)  50  vio-slt  T2/T4  CO "Tip" line 2 (or 4)  _| TO CO

     
     **  WARNING: When connecting primary set to CO telco lines: use 24/49 and 25/50 pairs.   **
     **  DO NOT attach the CO lines "1A2 style" to e.g. 1/26. Even though AT+T labels         **
     **  1/26 as T(1)/R(1) in the Com Key manual, these are Com Key's internal voice paths,   **
     **  and should not to be connected directly to the CO lines. (If you make this mistake,  **
     **  it'll "kinda work": you'll see lights and get dialtone, but Hold/Ring won't work.)   **
     **  The naming difference between T(1) vs. T1 is subtle; the former are internal voice   **
     **  paths, the latter are the actual CO lines.                                           **
     


                                * * *  S A T E L L I T E  S E T  * * *

                         BSP                                          BSP
           Pin  Color    Code   Description             Pin  Color    Code   Description
        _  ---  -------  -----  -------------------     ---  -------  -----  -------------  _
       |     1  blu-wht  R(1)   "Ring"                   26  wht-blu  T(1)   "Tip"           |
LINE 1 |     2  orn-wht  CA1    Common Audible 1         27  wht-orn  A(1)   A lead          |
       |_    3  grn-wht  LP(1)  Lamp                     28  wht-grn  LC(1)  Lamp Common     | 
        _                                                                                    |
       |     4  brn-wht  R(2)   "Ring"                   29  wht-brn  T(2)   "Tip"           |   Com Key
LINE 2 |     5  slt-wht  CA2    Common Audible 2         30  wht-slt  A(2)   A lead          |  "Internal"
       |_    6  blu-red  LP(2)  Lamp                     31  red-blu  LC(2)  Lamp Common     | signal paths
        _                                                                                    | for line 1-4
       |     7  orn-red  R(3)   "Ring"                   32  red-orn  T(3)   "Tip"           |
LINE 3 |     8  grn-red  CA3    Common Audible 3         33  red-grn  A(3)   A lead          |
       |_    9  brn-red  LP(3)  Lamp                     34  red-brn  LC(3)  Lamp Common     |
        _                                                                                    |
       |    10  slt-red  R(4)   "Ring"                   35  red-slt  T(4)   "Tip"           |
LINE 4 |    11  blu-blk  CA4    Common Audible 4         36  blk-blu  A(4)   A lead          |
       |_   12  orn-blk  LP(4)  Lamp                     37  blk-orn  LC(4)  Lamp Common    _|

            13  grn-blk  ICR1   Intercom#1 "Ring"        38  blk-grn  ICT1   Intercom#1 "Tip"
            14  brn-blk  DSS1   DSS Button #1            39  blk-brn  DSS2   DSS Button #2
            15  slt-blk  LCI1   Lamp Common Intercom#1   40  blk-slt  LPI1   Lamp Intercom #1

            16  blu-yel  ICR2   Intercom#2 "Ring"        41  yel-blu  ICT2   Intercom#2 "Tip"
            17  orn-yel  DSS3   DSS Button #3            42  yel-orn  DSS4   DSS Button #4
            18  grn-yel  LCI2   Lamp Common Intercom#2   43  yel-grn  LPI2   Lamp Intercom #2

            19  brn-yel  DSS6   DSS Button #6            44  yel-brn  DSS6   DSS Button #6
            20  slt-yel  COM    Power Supply Common      45  yel-slt  +V     Power Supply +
            21  blu-vio  DSS7   DSS Button #7            46  vio-blu  DSS8   DSS Button #8

            22  orn-vio  DSS9   DSS Button #9            47  vio-orn  DSS10  DSS Button #10
            23  grn-vio  COM    Power Supply Common      48  vio-grn  V+     Power Supply +
            24  brn-vio  COM    Power Supply Common      49  vio-brn  V+     Power Supply +
            25  slt-vio  COM    Power Supply Common      50  vio-slt  V+     Power Supply +


   WARNING: Although the Com Key 416 phones use regular 25 pair connectors, 
   and have many pins in common with 1A2, 1A2 and Com Key phones do not share
   compatible signals.
   
   For instance, on 1A2 systems it's common to use the yel-slt / slt-yel pair 
   for 90 volt ringing. On Com Key systems, this pair are V+ and COM respectively;
   a 1A2 ring voltage applied to that pair on any Com Key set would be bad.


Com Key 416 Related Acronyms and Abbreviations
----------------------------------------------

 ABR  - Automatic Button Restoration.

        Unlike the older 1A2 systems, when a line button is down on a Com Key
        416 set, when the user hangs up the phone, the button pops up.

        Presumably this is to prevent one from accidentally picking up on
        someone else's call in progress; with the older 1A2 systems, when you
        finished a call by hanging up, the line button you were using would
        remain down. If that line later came in use by someone else, and
        during their call you simply picked up the handset without first
        selecting an available line, you'd pick up on the other person's
        call-in-progress.

        The Com Key system seems to prevent this in two ways; by mechanically
        popping up all keys that are down when the handset is cradled (hung up),
        and also the privacy release feature would seem to prevent accidental
        (or intentional) "eves dropping" on calls in progress, unless the
        person using the line has hit "Privacy Release" to allow others to
        join the call.

 BIS  - Built In Speaker phone.

        This allows two-way conversation without using the handset.

        This is different from the "Built In Loudspeker" feature, which
        only allows monitoring of the conversation in progress, and not
        a two-way conversation.

 BSP  - Bell System Practices

        The BSP manuals are a collection of technical documents and addendum
        that describe the various phone systems the Bell System provided,
        including block schematics, and recommended configurations and procedures.

        There are three volumes; I, II and III.  
        Referenced here is Volume III, which is the only one of the three volumes
        that covered Com Key 416 and 718 phone systems.

 CO   - Central Office

        These are the raw POTS (Plain Old Telephone Service) lines that
        come in from the phone company (central office), each line a single
        pair of "Tip" and "Ring".

 DSS  - Direct Station Selection.

        The 'DSS keys" are the 10 white buttons along the top of the phone,
        which allow one to directly signal one of the other phones in the 
        system by voice.

        Each phone in the system can be assigned to one of the 10 DSS buttons
        via the 10 position slider switch located under the plastic "COM KEY"
        cover located between the two rows of DSS buttons.

        The position of this slider switch identifies that phone's extension
        number; so if the switch is set to '5', then anyone in the office
        pushing DSS button #5 will voice contact that phone. Normally one
        just pushes and holds the DSS button, and if a short tone is heard,
        one can begin speaking, their voice will be transmitted through 
        the called phone's speaker. If the called phone has a "Do Not Distrurb"
        feature, the caller will hear a steady tone when the DSS button
        is pressed.

        With only one Primary phone located on the system, there is only one
        intercom line available. When there are two Primary phones, two intercom
        lines are available.

        If a DSS button is held down, one can voice-signal the called party
        through the called party's speaker. Holding down several DSS keys
        could signal multiple phones at once. There is also a paging option,
        such that one of the 10 DSS keys could be assigned to paging speakers.

 HFAI - Hands Free Answer on Intercom

 MOH  - Music On Hold.

        When someone is put on hold, an audio source such as a radio station
        or tape player can be supplied via the MOH path.
 
 POTS - Plain Old Telephone Service

        The normal phone line service from the phone company, similar to what you
        find in homes; a line pair ("Tip" and "Ring") that are normally at 
        around 48 volts DC when idle, and has a approx. a 90 VAC ring voltage
        riding on top of that during ringing, and when the phone is picked up,
        the voltage drops to around 6 to 18 VDC when a conversation is in
        progress. When the far caller hangs up, most modern central offices
        send a CPC (Calling Party Control) signal, which is basically just
        a brief open circuit across Tip and Ring. This signal is used by
        phone equipment, such as when someone left on Hold abandons the call;
        the phone equipment knows to free up the line from Hold. Voice mail
        and answering machines use the CPC to prevent recording silence.

        You can usually hear CPC by picking up the phone and just listening
        to the dialtone.. at some point the CO times out, and interrupts
        the dial tone with CPC, followed by a recording that the phone is
        off the hook.


PRIV RLS - Privacy Release.

        This is a momentary push button below the SPKR button, second button
        down from the top in the vertical row of push buttons at the right 
        of the phone.

  R   - Recall button

        Similar to a 'hook flash', pressing this button is a way of signalling
        the PBX operator.

SPKR  - Speaker button

        When this button is locked down, the speaker is engaged, so that both
        sides of the conversation can be heard through the speaker.

        On BIS Satellite sets and HFAI sets equipped with a 4a speakerphone,
        this button is inoperative.


                                     -- [END] -- 



TODO: o Describe how to configure primary sets:
            a) For Line1/2 vs Line3/4 using internal connector
            b) To swap polarity of lines using internal connector
            c) To verify "SYS"/"SUPP" connector is properly configured

      o Adjust table to show actual voltage levels in place of V+ (eg. 24VDC)

      o Circuit description. Try tracing eg. line one 24/49 from CO into the
        comkey primary to see what route it takes through the circuit
        to get out on 1/26.

      o Details about the primary set (power supply, logic board, photos)


                              (C) Copyright 2008 Greg Ercolano.
              If you encounter errors in this document, please report them to: