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PXML No. BABT/PXML/PBX.0005
APPROVAL No. S/1207/23/F/500315 was S/2349/23/F/500315
 The GEC
28 (also known as the Interline 8) is an analogue Micro-PBX with a maximum capacity of 2
exchange lines and 8 extensions. It was made by GEC and introduced late 1985.
It consists of a compact wall mounted central unit which contains all the electronic
circuitry to operate the system. There are two major circuit boards contained within the
central unit, as well as the power supply for the system.
The main circuit board contains all the circuitry for 4 extensions, 2 exchange lines and 1
intercom circuit. The plug-on expansion board increases this capacity to 8 extensions, 2
exchange lines and 2 intercom circuits.
Any loop-disconnect, earth loop recall telephone approved to BS 6317 can be used as a
terminating station. All telephones are connected to the central unit by 3 wires, 2 for
speech and 1 for recall, apart from the mains fail extensions (extensions 1 and 2) which
require an extra wire as a bell wire under mains fail conditions.
The system takes its power from a mains supply. It will operate from a mains voltage of
220, 230, 240 or 250 volts a.c. at a frequency of 50 Hz. It has a power consumption of
less than 20 watts.
The terminating stations draw feed current from the PSTN during external calls, all other
power being provided by the power supply module.
The feed circuitry allows a maximum loop resistance from the GEC 28 central unit to a
terminating station of 30 ohms.
In the event of a failure in the mains supply, extension 1 will be switched through to
exchange line 1 and extension 2 connected to exchange line 2. No intercom facilities will
be available.
HARDWARE
The GEC 28 consists of a CCU incorporating case and base, 1 main PCB and 1 expansion
board.
PARTS
Item Description
D 142846E (or DPA 1409/A) 28 main PCB, version
D 142846G 28 main PCB, version
D 142847A (or DPA 1410/A) 28 expansion PCB
D 142402 Base assembly
D 141409 Transformer
Optional
D 143371 A or B Alerting device
SOFTWARE
Software generic on main PCB.
version Identification
Version A D142717/A
Version B D143177/B
Version C D143313/A
Version C D143313/B
Version D D143516/A
 PARTS LIST
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