SWITCHBOARD SA 8133

1. General
Switchboard, P.A.B.X., SA 8133 is the cordless manual switchboard for use with the P.A.B.X. 1.

2. Physical design

1. The colour of the switchboard is two-tone grey matching the Handset No. 3 .
   
   The switchboard is 19.5 in. wide by 8 in. high by 13 in. deep, weighs 25 lb. and is designed to stand on a desk.  It has a metal chassis and a plastic (ABS co-polymer) cover.
   
   
2. The cover is held in position by two angled brackets which pull the cover to the rear by means of the screws in the flange at the back of the baseplate.  To remove the cover the screws, which are captive, are released until the latching brackets spring clear of the projections on the inside of the cover.  The leading edge of the cover fits under the front of the face panel.
   
   
3. The chassis consists of three sections, the front and rear sections hinging on the baseplate and forming a triangle when the chassis is closed.  By releasing the screws at the apex the hinged panels can be opened outwards to give access to the wiring and components.
   
   
4. Connexions to the switchboard are made via a 71-way plug and socket-type connector, the plug being mounted on the baseplate (these are similar to the Connector No. 101).
   
   
5. The operator’s handset connects through a plug to a Jack No. 84C fitted on the left-hand side of the rear flange of the baseplate and rests on a cradle on the left-hand side of the switchboard.  If required, an additional Jack No. 84C may be mounted on the right-hand end of the baseplate flange in place of the dummy button.  The wiring for this jack is tied back in the cable form.  The cradle may be moved to the right-hand side of the cover by unscrewing it and inter ­ changing it with the dummy buttons on the right.
   
   
6. The switchboard is not designed for use with a lightweight headset.
   
   
7. The face equipment comprises a dial and a number of push-button keys, as detailed below.

(i) Eighteen connecting keys are provided for exchange, inter-P.B.X., manual extension and 0-level lines.  These keys are locking and contain lamps on which calling and supervisory signals are given.

(ii) Eleven common service keys, all without lamps, designated as follows:

(iii) Ten non-locking digit keys.  There is space for fitting two additional keys, one for auxiliary night service and the other for any special facility that may be required.

3. Position keys
The common service position keys are used as follows:

1. Dial key - For connecting the dial to exchange, automatic inter-P.B.X. and manual extension circuits.
   
2. Ring key - For ringing on 0-level and manual extension circuits, and on generator signalling inter ­ P.B.X. circuits.
   
3. Interrupt key - Enables the P.B.X. operator to offer a call to an engaged extension. (A ticking noise is superimposed on the extension circuit when the operator enters the connexion to warn the extension that the operator is in circuit.).
   
4. Flash and cancel key - Enables the operator to recall the public exchange operator on an established call, or to release the connexion after a dialling error.
   
5. Speak extension and speak exchange keys - Enable the operator to speak on either the extension or the public exchange side of a connexion without the other party overhearing.
   
6. Engaged test key - Enables the operator readily to ascertain free lines. Operation of the key causes a steady glow on the supervisory lamp associated with any exchange, inter-P.B.X. or manual extension circuit in use (see also par. 5).
   
7. Release Key - Enables the operator to release an exchange line which has not been keyed to an extension number, or to correct a keying error.
   
8. Alarm cut-off key - Disconnects the audible alarm signal in the event of a mains fail or other alarm.
   
9. Audible alarm key - While this key is operated an audible signal is given on every calling circuit by means of a buzzer.
   
10. Night service key - This key is operated when the operator vacates the switchboard.   The operation of the key arranges for calls incoming on exchange and inter ­ P.B.X. circuits to be answered at extensions by dialling 8 to gain access to the calling line.
    
11. Auxiliary night service key - This key may be fitted when required to provide direct exchange night service for selected extensions.

4. Digit keys
Digit keys are provided for keying extension numbers only.  They are connected to a marker circuit which positions the linefinder of exchange lines, inter-P.B.X. circuits and the 0-level circuits onto the keyed extension number.  The digit keys and marker circuit do not give pulse signals and cannot, therefore, be used for calls to the public exchange.

5. Calling and supervisory lamps
One lamp is provided for each exchange line, inter-P.B.X., manual extension and 0-level circuit. These lamps function as calling and supervisory lamps. The signals given are as follows:-

1. A flicker signal - 0.2 second on, 0.2 second off -indicates a calling circuit.
   
2. A steady glow on a lamp during the setting-up of a connexion indicates a free extension.  This glow ceases when the extension answers.
   
3. A flashing signal - 0.75 second on, 0.75 second off - indicates a busy extension.

The appropriate supervisory lamps glow steadily when the ENGAGED TEST key is operated, to indicate a busy exchange line, inter-P.B.X. or manual extension circuit.

6. Alarm lamps
Three lamps to indicate various alarm conditions are provided as follows :-

1. P.G. pilot - This lamp is fitted with a white opal and, when glowing, indicates a faulty line or a permanent loop due to either a displaced handset or a handset not replaced after a call. The P.G. extension may be located by keying each extension number in turn, via an 0-level circuit, until the lamp in the 0-level line key is darkened.  The last extension keyed is P.G. If only one extension is P.G. then the P.G. pilot lamp will also be darkened.
   
2. Mains fail - This lamp is fitted with a red opal and, when glowing, indicates failure of the mains supply.
   
3. Auto alarm - This lamp is fitted with a red opal and, when glowing, indicates an alarm-type fuse has blown, a selector failing to release, loss of ringing supply or failure to clear of associated S.S.A.C. 13 equipment (when fitted).

7. Dial
This is provided to enable the operator to originate exchange calls or to complete calls for manual extensions.  It is also used for dialling over automatic inter-P.B.X. lines.

8. Operator’s telephone
This is a Handset No. 3, Grey, with Plug No. 420 Grey 3A, which is requisitioned separately and fitted locally.  The operator’s circuit is electrically unsuitable for the use of a light ­ weight headset, e.g. Headset No. 1 .

9. Buzzer
Audible alarms are given by an electronic buzzer which can be arranged to give soft, medium or loud sound as desired.  The setting used should be such that the buzzer can be heard adequately over the maximum ambient noise encountered.

10. Operation
Detailed operating instructions are issued on form A 1165.  Briefly, the operating procedure for the switchboard is as follows

An incoming call is indicated by a flicker signal on the appropriate lamp (and operation of the buzzer if the audible alarm key is operated).  To answer, the key in which the lamp is flickering is depressed.  The lamp will continue to flicker.  The required extension number is keyed on the digit keys.  If the extension is free, the flicker signal on the lamp will change to a steady glow to indicate that the extension is being rung.  The key may now be restored to normal (by a further depression).  When the extension answers the lamp will cease to glow.

At the conclusion of the call the connexion will be cleared automatically without further action on the part of the operator.

If the extension keyed is busy, the flicker signal will change to a busy flash.  If the calling subscriber is prepared to wait, the key may be restored to normal.  The lamp will then continue to flash until the extension becomes free.  The caller is then connected automatically to the extension without further intervention by the operator.

11. Maintenance
The following points should be noted:-

1. To remove the dial it is necessary to remove the clamping ring (held by three nuts) from the baseplate before removing the dial from the clamping ring.
   
2. Adjustment of the digit keys is not possible, faulty keys must be changed.
   
3. Access to the lamps in the 2000-type keys is gained by removing the key button.

12. Cabling
Connexion to the automatic equipment is by Cable, P.V.C., No. 3A, 75-wire 6.5, being terminated at the switchboard end on a socket for connexion to the plug in the switchboard.

13. Diagrams
Diagram SA 8133 shows the circuit arrangements of the switchboard, which are described in Diagram Notes SA 8134.

Last revised: January 30, 2021