BABT/PXML/23 PBX.0016 (TSX50) &
BABT/PXML/23 PBX.0004 (SX50)
APPROVAL No. NS/1412/23/F/600046 (SX50)
Click here to see information on BT's withdrawal of
Subscribers Private Metering (SPM)
First made by Mitel in 1985 this switch was originally called the SX500, with BT naming it the Dekara. In 1986 the system
was renamed as the Mitel SX50 and the BT TSX50.
The SX 50 is a micro processor controlled switching system that uses a digital switching
matrix for the connection of calls. TSX 50 was released in 1987 with Generic 3543.02 (UK1)
software. The introduction of Generic 3543.03 (UK2) software in May 1989 allows the use of
a Visually Handicapped Operators Console (VHOC) attachment and,
with a new power supply PSU2A increased system capacity from 80 to 160 ports.
System capacity will depend on the type of power supply unit (PSU 1A or PSU 2A) - see
table below. Note that the quoted capacities cannot all be achieved at the same time, due
to a limitation of 10 interface card slots per system.
Generic 3546.01 (UK3), released in June 1990, introduced Automatic Route Selection (ARS),
Remote Access (RMATS), and other facility enhancements detailed in the system
Increased capacity can only be offered when using Generic 3543.03 or 3546.01 software with
the PSU 2A.
In 1994 DASS2 connectivity was announced and this used the Interconnect 200
box in conjunction with the SX50 DNC card (which supported DPNSS). It is debatable whether BT sold any.
The system could be fitted with Superset 4, Superset 400 type telephones or one switchboard.
INTERFACE TYPE MAXIMUM CAPACITY . PSU 1A MAXIMUM CAPACITY . PSU 2A
(Generic 3543.02/3546.01) (Generic 3543.03/3564.01)
EXTENSIONS 80 (5 CARDS) 160 (10 CARDS)
EXCHANGE LINES 24 (3 CARDS) 32 (4 CARDS)
PRIVATE CCTS 12 (6 MOTHER CARDS) or
SSDC5 ANY MIX UP TO 8 24 (6 MOTHER CARDS) or
AC15A (4 MOTHER CARDS) + MAX OF 6,MOTHER CARDS
TX14 EXTENSIONS 32 (4 CARDS) 32 (4 CARDS)
In exceptional circumstances, where six module mothercards are fully equipped with AC15A
and/or DC5A modules and a remote maintenance module is also required, a seventh module
mothercard can be provided. However, it must be equipped with the remote maintenance
Standby Power may be provided using BT Power System 250G, which is an Uninterruptable
Made by Mitel Telecom Limited
SEVERNBRIDGE INDUSTRIAL ESTATE, PORTSKEWETT, NEWPORT, GWENT. NP6 4YR
Tel 01291 430000
NOTE: TSX 50 and SX 50 ARE DESCRIBED IN SEPARATE PXML's.
For TSX 50 approved as described
in BABT/PXML/23 PBX.0016.
For SX 50 approved as described in BABT/PXML/23 PBX.0004.
BT systems were later shipped from Mitel with the Generic 3546.01 (UK3) software module as
The Lithium battery in the Generic Module must be replaced every ten years. The battery
can be replaced WITHOUT powering down the system. Click
here for battery type.
Note: if the Lithium battery is replaced, when there is no power, then loss of customer data
Remote access facilities for maintenance will be provided as a standard feature on all
Generic 3546.01 (UK3) systems.
The System warranty is 15 months from the manufacture date. Repaired cards carry
outstanding system warranty or 3 months whichever is the greater. New cards carry 15
months warranty from date of manufacture. The TSX 50 will carry a date code identification
(DD/MM/YY) in addition to a bar code, thus enabling the user to ascertain warranty status
without contacting Mitel repair centre. The date code is applied to chassis consoles and
the solder side of PCB's.
Power Unit 1A can only be used on systems with a maximum of 80 port capacity.
Power Unit 2A may be used on all systems to a maximum of 160 port capacity.
To maintain VHOC sites and 160 port capacity systems software level G3543.03 is
required. As this software level is backward compatible with all previous TSX50 systems.
Taken from BT information.
General Information on the SX50 - UK3 variant (1989)
The SX50 is an Integrated Communications System using an innovative, compact modular design which allows easy
system expansion, fault finding and card replacement. SX50 is a digital electronic system, using stored program control and
advanced digital architecture.
SX50 has a very wide range of features and can accommodate
(in the UK) up to 160 extensions, 32 Exchange Lines, 24 Private Circuits, and up to 32 SUPERSET
4 telephones, depending on
system configuration. SX50 can be adapted by data changes to match a wide range of public exchanges. Although cost-effective as a
basic telephony switch, the SX50 has been designed as an integrated voice and data switch. This means that it can be adapted
to handle future communications applications including voice, data, text and image.
SX50 meets the requirements of BSI (BS6450) for Private Branch Exchanges. SX50 is approved by the
British Approvals Board for Telecommunications (BABT), Approval Number NS/1412/23/F/600046.
SX50 provides the wide range of features normally provided with MITEL switching systems, as well as;
Low power consumption
Small number of types of assembly, for simplified spares holding
Simultaneous use of MF4, dial pulse and SUPERSET telephones
Selection of fixed or flexible extension numbering scheme
Selection from a wide range of applications packages
Operation with or without SX50 Console
Operation with SUPERSET 4 Console
Visually Handicapped Operators Interface Unit
Capability of Private Circuit interconnection with other PABXs
Call Information Logging
Emergency switching in the event of a power supply failure
The main components of an SX50
system are as follows:
A wall mounted SX-50 equipment cabinet containing Printed Circuit Cards.
The operators console.
The Test Jack Frame.
Cables connecting the power supply unit to the wall socket, between the equipment cabinet and the console,
and connecting the Extension and Trunk Cards to the Test Jack Frame.
The Backplate for the SX50 equipment cabinet is fixed to a wall. The Card frame is attached to the
Backplate. The Motherboard is inserted, followed by the power supply unit which
is clipped to the side of the frame. Finally the Generic Module is clipped to
the right hand side of the frame and connected to the Motherboard. The printed circuit cards
can now be inserted. After this the cables are
installed from the equipment cabinet to the mains socket and to the Exchange Lines and extensions, via the Test Jack Frame.
The cable to the console can be connected through the Test Jack Frame or directly to the Control Card.
SX50 can be used with loop disconnect dial, MF4 keypad and self contained (Decadic) keypad telephones
in any combination. In addition, MITEL SUPERSET 4 electronic telephones which provide many additional facilities, can be used. Telephones to be connected directly to Exchange Lines in the event of a power failure MUST be
compatible with the local Exchange. If Earth Calling Exchange Lines are used, an Earth Recall button must be provided for these
Customer Data Entry
After installation, the installation engineer powers up the system and carries out customer data entry
from the console. This data defines the various features required by the customer and matches the system to the local Exchange
Lines. The configuration of an SX50 system can be altered by redefining some of the data. The customer is allowed to change
some of the data if required. A security code prevents unauthorised access to the system.
The digital switching matrix in the SX50 is totally non-blocking for the maximum configuration of 32 Exchange Lines or 160 extensions.
Every five years the small lithium battery in the Generic Module must be replaced. Apart from that, no
routine maintenance is required or recommended. Click
here for battery type.
Diagnostics and Fault Correction
The SX50 uses comprehensive automatic diagnostic procedures which run continuously and indicate, on the
console, any faults that may be detected. In general, if a non urgent fault is detected, the system isolates and busies out the
faulty circuit and continues operation though possibly with reduced performance. Detailed diagnosis of faults can be carried out
at the console. Site work is limited to changing specific plug-in modules or boards and the modular design makes this quick and
simple. Background diagnostics can also be run on demand.
If SX50 suffers a power failure, the system automatically goes over to Emergency Switching Mode, in
which up to 10 Exchange Lines can be mechanically switched to selected extensions. These extensions are then powered from the local exchange, enabling some external communication from the system. When power is restored, normal operation resumes. Customer data is held during power failure by the Lithium
battery in the Generic Module.
A printer or recorder can be used:
for Call Information Logging,
for logging the use of Wake-Up Operator Controlled calls in a hotel,
for printing out the contents of the extension meters,
by the maintenance staff for Customer Data Dump and Load and logging Alarms.
Briefly, SX50 requires an office environment which remains within the limits:
Temperature 0°C to 40°C
Relative humidity 10% to 90% non condensing
SX50 is resistant to electro-magnetic interference expected in ordinary conditions and does not emit electro-magnetic radiation likely to affect most
users. There is no fan and acoustic noise is
well below accepted limits.
BRIEF CABINET DESCRIPTION
The equipment cabinet consists of three main components, a Backplate, a Card frame and a Cover. The SX50 Cabinet must
be wall mounted.
An assembled, fully equipped equipment cabinet, weighs
The Generic (or Memory) Module is fastened to the right hand side plate of the Card frame. It is an enclosed circuit
board containing the system memory and a Lithium battery which protects the memory from loss of data for up to 10,000 hours if the
mains power supply fails.
Power Supply Units
Two Power Supply Units are available, the 140W unit and the 225W MK2 unit. The 225W unit provides extra capability by allowing a
larger system configuration to be used. The Power Supply Unit is clipped to the left side of the Card frame and can be readily removed.
The 140W Power Supply Unit is used with configurations up to 80 extensions or 24 Exchange Lines. If more than 80 extensions or 24
Exchange Lines are to be connected to the system, the 225W Power Supply Unit MUST be installed.
The 225W MK2 Power Supply Unit requires 1.3 amps at 240 volts and provides a continuous output of 225 Watts. The 140W Power Supply
Unit requires approximately 1 amp at 240 volts and provides a continuous output of 140 Watts. Both Power Supply Units are protected by
The Control Card MK3 is situated at the back of the Card frame, parallel to the wall, and plugs directly into the Power
Supply Unit. The Control Card carries:
Connectors for up to ten Peripheral Cards.
The Central Processing Unit.
Digital cross point switches.
Call processing circuits.
Timing and synchronisation circuits.
Music on Hold/Paging circuits.
Music on Hold/Paging Terminal Strip.
A seven segment LED display.
Four Status switches.
One Reset switch.
Night Bell Terminal Strip.
Voltage Test Points.
The Peripheral Cards all plug into the Control Card, perpendicular to the wall, so that their front edges are exposed. It is possible to
withdraw the Peripheral Cards sufficiently to allow the Control Card to be removed and replaced, without having to remove the front
connectors on the Peripheral Cards.
Music on Hold/Pager and MF4 circuits. These audio and control circuits for Music on Hold and for the paging system are now carried
on the Control Card MK3. Additional circuits allow SX50 to support MF4 signalling over Exchange Lines.
Five types of Peripheral Card (Extension, SUPERSET, Trunk, Digital Network Card and Universal Card) are used in SX50. These are
available in the following versions:
16 circuit ONS (Extension) Card
8 circuit ONS (Extension) Card
8 circuit COV (SUPERSET) Card
8 circuit Trunk Card with 50 Hz Meter Pulse Detectors
4 circuit Trunk Card with 50 Hz Meter Pulse Detectors
Digital Network Card
The Universal Card is designed for a variety of peripheral functions and is configured by attaching
removable modules. Up to four single-sized modules or two double-sized modules can be plugged in to each Universal Card. The
modules use two connectors per single module or three connectors per double module. A group of four red LEDs on the front of the
Universal Card indicate the status of the modules and a single green LED indicates the status of the card. There is a connector at
the front for the cable to the Test Jack Frame. Three types of plug-in module are available for different configurations of the
Universal Card. These are:
SSAC15A Module. This is a single sized module. Each module provides the circuits for. one SSAC1S Private
SSDC5 Module. This is a double sized module carrying the circuits for one SSDC5 E&M Private Circuit.
RMATS Module. This single sized module allows data entry and fault location to be carried out from a remote
The ONS (Extension) Card. Two versions of this card provide the circuits required for either eight or
sixteen dial pulse or MF4 extensions. There is a connector at the front for the cable to the Test Jack Frame and there are
also red LEDs to show the status of the extensions and one green LED to indicate the status of the card.
The COV (Control Over Voice) (SUPERSET) Card. This card can accommodate eight SUPERSET 4 telephones. Each
COV Card has eight red LEDs to display the status of the SUPERSETs and one green LED to indicate the status of the card. There is a connector at the front for the cable to the Test Jack
Trunk Card. Each Trunk Card provides the circuits required for four or eight Exchange Lines. A connector
is provided at the front for the cable to the Test Jack Frame and there is a row of red LEDs to give an indication of the status
of the Exchange Lines together with one green LED which indicates the status of the card.
BRIEF CONSOLE DESCRIPTION
The Operators Console is a moulded plastic unit, weighing 1.8 kg. A connecting
cable at the back of the Console can be run to the TJF or directly to the Control Card. On the left side of the Console is a
double socket for plugging in the operators handset or headset On the right side there is a standard 12 key dial pad with the
numerals 0 to 9 and and #. On the right of the dial pad there are an additional four keys used for adjusting the display
contrast and the volume of the bell. On the front panel of the console there is a Liquid Crystal Display (LCD) two characters high
and forty characters wide which is used to display information to the operator or maintenance engineer. Directly below the LCD
display is a row of five marked Display Assigned keys. A further three rows each of seven keys with their functions marked
above them are also fitted on the console.
Operation of the console is fully described in the Console Operating Instructions. The functions of the
keys are briefly described here.
Display Assigned Keys
The upper five keys are Display Assigned Keys. They have no permanent markings but always assume the functions shown in the display above them. These displays change according to the mode of
operation at the time. When a key does not have a display, pressing it does nothing. During data entry, the functions are chosen
ENTER, NEXT, EXIT, QUIT, SAVE, and --->
and during normal call handling, the five keys become:
GRP 1, GRP 2, GRP 3, DIAL 0 (or PRI 0), and RECALL
These represent the six categories of call that the operator can select for attention.
There are 21 function keys. Fourteen of these keys can have their assignments changed by data entry. There
are 15 possible key assignments. These keys are used during call handling and are fully described, together with their operation in the Console Guide. The default functions of these keys are listed below for reference:
FUNCTION, STATUS, TRUNK, BARRING, OVERFLOW, PAGE, CANCEL, WAKE UP, EXT METR, INTRUDE, MESSAGE, BOTH, SPLIT, RELEASE, BELL, NIGHT, ALARM,
HOLD 1, HOLD 2, HOLD 3, ANSWER.
An ACCOUNT key for use with Account Codes can also be assigned by data entry.
BRIEF SUPERSET 4 DESCRIPTION
The SUPERSET 4 is a microprocessor controlled electronic telephone. It has a row of multi-function
keys, linked to a visual display, for PABX feature access which eliminates the need to remember access codes. It also has 15 line
selection keys and a line status display which gives the SUPERSET 4 the facilities of a key and lamp system. Any unused line
selection keys can be used as Abbreviated Dialling keys.
In addition, the SUPERSET 4 offers full Loudspeaking Telephone working, ringer pitch and volume controls,
an On-hook Dialling facility and a dedicated Hold key.
Up to 32 SUPERSET 4 electronic telephones can be installed on an SX50 system.
One SUPERSET 4 can be used as a SUPERSET Console if required.
SX50 can accommodate up to 10 Peripheral Cards. These cards can work in almost any combination, so that
the required customer con
figuration can be achieved. There are several circuit card limits which MUST NOT be exceeded. Depending on the Power Supply Unit
fitted, these maxima are:
With the 140W Power Supply Unit, 24 Exchange Lines, 8 Private Circuits, 80 extensions, (or 32 SUPERSET 4s
and 16 extensions).
With the 225W Power Supply Unit, 32 Exchange Lines, 24 Private Circuits, 160 extensions, 32 SUPERSETS. The
installer can configure the SX50 in any way he chooses but MUST NOT exceed the circuit card limits. The choice of circuit cards MUST be made
carefully, so that there are no more than 10 cards and that the limits are not exceeded.
Up to 10 Peripheral Cards can be installed, but the following numbers of individual circuit cards must not
be exceeded when using the 140W Power Supply Unit, NOT MORE THAN:
five ONS (Extension) Cards,
four COV (SUPERSET) Cards,
three (8 circuit) Trunk Cards,
six (4circuit) Trunk Cards,
four Universal Cards,
one Digital Network Card, (NOTE: This card uses two card slots)
eight SSDC5 and SSAC1SA modules,
one Music on Hold/Pager/MF4 module.
one RMATS module can be installed.
With the 225W Power Supply Unit installed, the limits are,
ten ONS (Extension) Cards,
four COV (SUPERSET) Cards,
four (8-circuit) Trunk Cards,
eight (4-circuit) Trunk Cards,
six Universal Cards,
one Digital Network Card, (NOTE: This card uses two card slots)
twelve SSDC5 modules,
twenty-four SSAC15A modules,
one RMATS module can be installed.
These rules allow many possible configurations.
The SX50 has a maximum capacity of 24 Exchange Lines, (140W Power Supply Unit) or 32 Exchange Lines with
the 225W Unit. These lines can be accommodated by either 8 circuit Trunk Cards, or combinations of 4 and 8 circuit Trunk
Cards so that the limits are not exceeded.
The SX50 has a maximum capacity of 80 extensions (140W Power Supply Unit) or 160 extensions with the
225W Unit. These extensions can be accommodated by either 16 extension ONS Cards or combinations of 8 and 16 extension ONS Cards so that the limits are not
SUPERSET (COV) Cards
SX50 has a maximum capacity of 32 SUPERSET 4 telephones using either Power Supply Unit. These
SUPERSETs can be accommodated by up to 4 x 8 circuit COV Cards.
Note: Each SUPERSET is equivalent to TWO normal extensions in capacity calculations.
Universal cards provide connections for various modules. Up to four modules can be connected to each
Universal Card. SX-50 has a maximum capacity of 8 Private Circuits (140W Power Supply Unit) or 24 Private Circuits using the 225W
unit These can be any combinations of SSDC5 circuits (which use a double module) or SSAC15A circuits (which use a single module), as long as the totals are
In addition a combined Music on Hold/Pager/MF4 module can be installed, using one module position. (Note
that these circuits are now available on the MK3 Control Card).
The Universal Card can also carry a single RMATS module which uses one module position. Refer to Volume
Two, Applications Manual.
Digital Network Card
A Digital Network Card using two card slots, can be installed to provide 30 channels of voice and data
between two or more SX50 with Digital Network Cards installed. Refer to Volume Two, Applications Manual for further details of the Digital Network Card.
Because SX50 is a modular system with plug-in printed circuit cards, it can be expanded by installing
additional plug-in cards in the equipment cabinet. The smallest SX50 installation would have 4 Exchange Lines and 8 extensions. This could be increased by installing extra circuit cards to achieve the desired
Apart from the additional cards or modules, expansion requires additional customer data entry and cabling. If more than 80 extensions or 24 Exchange Lines are required, the 225W Power Supply Unit
MUST be installed.
VISUALLY HANDICAPPED OPERATORS INTERFACE UNIT
An Interface Unit, designed for use by visually-handicapped Operators is available with the SX50.
SX50 System Features
160 Port Working
SX50 can support full 160 port working, with up to a maximum of 32 Exchange Lines or 160 extensions. The 225W Power Supply Unit MUST be installed on systems with more than 80 extensions.
This feature allows SX50 to store a maximum of 90 or 900 telephone numbers. If the option to store 90
numbers is selected, then each number can contain up to 26 digits. If the option to store 900 numbers is selected, then it is not
possible for all the numbers to contain 26 digits. Numbers can still contain up to 26 digits, but a system digit limit will be
reached. (For example, it is normally possible to store more than 800 numbers containing 10-digits each). The operator and
permitted extension users can dial these numbers by dialling a three or four digit access code.
Click here for Maintenance information