8525B/8528 Technical Service Manual 4-1
Publication No: 15-02036 Issue 6
4 Technical Description
This section of the manual contains a detailed description of the circuitry
used in the land and marine transceivers and associated control heads.
Unless otherwise stated, the description applies equally to the 8525B, 8528
and 8528S transceivers.
All circuit paths of the following PCB assemblies are made through the
Motherboard and Chassis (04-02453), where the connector and pin numbers
of the interconnections are shown:
RF Mixer & Dual Synthesizer (04-02450)
Audio & IF 1650kHz (04-02093)
Microprocessor Controller (04-02451 and 04-03031)
Display PCB (04-02579) (8525B)
Display PCB, LCD (04-02454) (8528)
PA & Filter (04-02452)
PA/Exciter Interface (04-02434)
4.1 Control and Supply Voltages
All switching, except ‘power-on’, is controlled either directly or indirectly
by the microprocessor on the Microprocessor Controller PCB.
4.1.1 Supply Voltages
The supply voltages used are as follows:
• ‘A’ rail—unregulated battery supply.
• ‘B’ rail— +10 Volt regulated supply derived from the ‘A’ rail.
• Volt supplies—individual three-terminal regulators supplied from ‘A’
rail.
• Volt supply—‘pump up’ switching supply on the RF Mixer and Dual
Synthesizer PCB (IC1).
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