4-16 Technical Description 8525B/8528 Technical Service Manual
Issue 6 Publication No: 15-02036
4.6 Motherboard and Chassis (04-02453)
The Motherboard interconnects circuit boards which are mounted directly on
it and provides connections to other assemblies mounted on the chassis. It
also provides connections which link these assemblies to external
connectors. In addition the board carries components associated with these
interconnections and with the power supplies and their switching.
4.6.1 Power Supplies
The Motherboard contains relays with their switching transistors associated
with the power supplies as described in Section 4.1.
The board also contains two voltage regulators, IC1 and IC2. These provide
stabilised DC supplies of 10V and 5V respectively from the A battery
supply. The 10V and 5V supplies are used throughout the transceiver.
4.6.2 Antenna Control Facility
The Antenna control socket J201 on the rear panel of the transceiver
provides an interface for various antenna tuning systems. The socket is
connected to P201 on the Motherboard. Interconnections within the
Motherboard provide access to the 12V supply, 4-bit binary-coded data
indicating the channel selected, and various other outputs for use by
automatic tuning systems. On entering the board the lines are filtered to
prevent RF picked up on the external cable, from interfering with the
operation of the transceiver. The table in Section 1.2.4 shows the pin
connections and the signal level of each function.
4.6.3 Extended or Remote Control—Option R
The Remote Control plug (P502) on the rear panel of the transceiver
provides an interface for extended or remote control equipment. When fitted
the plug is connected to the Remote Control and Filter PCB mounted on the
Motherboard. Transceivers manufactured for extended or remote control
include these components. Transceivers with front panel controls can have
them fitted as Option R.
The extended or remote control lines carry the services shown on the circuit
diagram. Components on the Remote Control and Filter PCB prevent RF
picked up on the external cable, from interfering with the operation of the
transceiver.
The table in Section 1.2.4 shows the pin connections and levels of each
function.
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