8571—Technical description
336 NGT Transceiver System Technical Service Manual
Backplane and power supply
The Backplane PCB provides the interconnections between the PCBs fitted to the 8571.
It contains the transmit audio bus and receive audio bus, the I
2
C bus, the 30 kHz clock,
the 300 Hz detect and the regulators for the DC supplies.
The 8571 operates on 12 or 24 V. For 24 V operation, the DC is connected to two
regulators (drawing 04-02691), IC1 for 5 V (+5 rail) and IC2 for approximately 14 V
(A rail). For 12 V operation, only IC1 is required and IC2 is bypassed by D4. Reverse
voltage protection is achieved by the series diodes D1 and D2.
The Backplane PCB also provides connectors P6 and P105 for fitting links to disable the
unused lines on the Dual Line Equaliser PCBs (drawing 04-02541) as required. Also
P303 and P304 provide the connectors for fitting the RS232 strapping.
All external input/output connections to the 8571 are made via interface cables
connected to the Backplane PCB. Some interface cables include isolation transformer
assemblies, which are required for 2-wire or 4-wire operation.
Drawings 04-02691 and 04-02541
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