| P.O. ENGINEERING DEPT
Issue 1, Oct 1969
SWITCHBOARD, P.A.B.X., SA 8133
Switchboard, P.A.B.X., SA 8133 is the cordless manual
switchboard for use with the P.A.B.X. 1.
2. Physical design
- 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.
- 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.
- 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.
- 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
- The operatorís 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.
- The switchboard is not designed for use with a lightweight
- 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:
||Flash and cancel
(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:
- Dial key - For connecting the dial to exchange, automatic
inter-P.B.X. and manual extension circuits.
- Ring key - For ringing on 0-level and manual extension
circuits, and on generator signalling inter ≠
- 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.).
- 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.
- 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
- 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).
- 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.
- Alarm cut-off key - Disconnects the audible alarm signal in
the event of a mains fail or other alarm.
- Audible alarm key - While this key is operated an audible
signal is given on every calling circuit by means of a buzzer.
- 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.
- Auxiliary night service key - This key may be fitted when
required to provide direct exchange night service for selected
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
- A flicker signal - 0.2 second on, 0.2 second off -indicates
a calling circuit.
- A steady glow on a lamp during the setting-up of a connexion
indicates a free extension. This glow ceases when the
- 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
- 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.
- Mains fail - This lamp is fitted with a red opal and, when
glowing, indicates failure of the mains supply.
- 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).
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. Operatorís telephone
This is a Handset No. 3, Grey, with Plug No. 420 Grey 3A, which
is requisitioned separately and fitted locally. The
operatorís circuit is electrically unsuitable for the use of a
light ≠ weight headset,
e.g. Headset No. 1 .
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.
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
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.
The following points should be noted:-
- 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.
- Adjustment of the digit keys is not possible, faulty keys
must be changed.
- Access to the lamps in the 2000-type keys is gained by
removing the key button.
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.
Diagram SA 8133 shows the circuit arrangements of the
switchboard, which are described in Diagram Notes SA 8134.