Block Diagrams - Sony WRR-855B Service Manual

General Description
The WRR-855B consists of the following circuit boards:
Board Name Quantity
TUN-8 board 1
CPU-342 board 1
DP-236 board 1
SW-814 board 1
TUN-8 Board
The TUN-8 board is powered by the DC +7 V power
supply and functions as the PLL synthesized diversity
tuner which is controlled by the CPU-342 board. The
TUN-8 board receives the RF signal input from the
antenna A and antenna B, and outputs the demodulated
audio signal. The TUN-8 board also supplies the RSSI
signal and the DC-converted audio signal to the CPU-342
board. The TUN-8 board consists of the power supply
block, RF block and the audio block.
The power supply block receives the DC +7 V power input
which is supplied from the D-sub connector via CN602.
The power supply block supplies DC +6 V (IC651) to the
RF block and audio block from the voltage regulator IC651
and IC652. It supplies DC +5 V (IC652) to the 1st local
circuit of the RF block.
The RF block consists of RF amplifier circuit, 1st mixer
circuit, 2nd mixer circuit, IF circuit, FM detector circuit,
1st local circuit and 2nd local circuit. Two equivalent
circuit of the RF amplifier circuit, 1st mixer circuit, 2nd
mixer circuit, IF circuit and FM detector circuit are
provided for antenna A (Ref. No. 100s) and for antenna B
(Ref. No. 400s).
The RF signal which is input from the antenna A and
antenna B are passed through band-pass filters (FL101,
FL401), amplified by RF amplifiers (Q101, Q401), passed
through band-pass filters (FL102 and FL402) and input to
1st mixer circuit. The RF signal is mixed with the 1st local
signal in the 1st mixer circuit (Q102, Q103, Q402, Q403)
where the input signal is converted to the 1st IF signal
(150.75 MHz). The 1st IF signal is mixed with the 2nd
local signal at the 2nd mixer circuit (Q104, Q105, Q404,
Q405) where the 1st IF signal is converted to the 2nd IF
signal (10.7 MHz). The 2nd IF signal is detected by the
FM detector IC (IC102, IC402) which outputs audio (AF)
signal. The audio signal is sent to the audio block. The
2nd IF signal is converted to the RSSI signal by the IF
amplifier (IC101, IC401) and is output to the CPU-342
board. The 1st local signal is generated by controlling the
VCO (CP301) with the PLL IC (IC301). The 2nd local
signal is generated by the crystal oscillator (CP302).
WRR-855B
Section 6

Block Diagrams

The audio block consists of the tone signal detector circuit,
noise signal detector circuit, diversity switching circuit,
muting circuit, de-emphasis circuit, expander circuit and
Reference No.
audio amplifier circuit. The FM detector outputs (audio
outputs AF (A) and (B)) of the RF block are amplified by
100 to 400 and 600s
the AF amplifier (A) (IC201) and AF amplifier (B)
700 series
(IC202) and is sent to the diversity switching circuit
800 series
(IC203-1/3). The diversity switching is controlled by the
900 series
DIV signal from the CPU-342 board. The audio output
signal from the diversity switching circuit is passed
through the muting circuit (IC203-2/3), de-emphasis circuit
(IC204), low-pass filter circuit (IC205) and expander
circuit (IC206) then amplified by the AF amplifier
(IC207) and feed the D-sub connector via CN602.
CPU-342 Board
The CPU-342 board consists of the CPU which performs
the system control, and the system clock oscillator circuit.
The CPU (IC701) controls the TUN-8 board, DP-236
board and SW-814 board.
The clock oscillator circuit (X751, CT751, IC751, IC752,
etc.,) oscillates the 4 MHz clock which is fed to the tuner
unit. The 4 MHz signal is multiplied (IC780) to generate 8
MHz signal which is supplied to the CPU. 4 MHz clock
can be input to the WRR-855B from external source. If
external clock is input, clock signal is switched from the
internal clock to the external clock automatically by IC772,
IC773, IC774, etc.
Connector CN761 is the connector for external interface
which relays the serial I/O signals of the CPU (IC701) and
external controller. IC761 shifts the level (TTL ↔ RS-
232C) of external interface signal of the CPU.
DP-236 Board
The DP-236 board consists of display block and operation
control block.
The dipslay block has the LCD (ND801) which indicates
the various status of groups and channels, and the RF
indicator (D801) and the AF indicator (D802) which
indicates status of RF input and audio input. The operation
control block consists of the switches (S801 to S804)
which perform the various settings such as group setting
and channel setting. When these switches are operated, the
various settings are performed by the CPU on the CPU-
342 board.
SW-814 Board
The SW-814 board has the POWER ON/OFF switch
(S901) and the MUTING ON/OFF (S902) switch on it.
IC901 and Q901 control ON and OFF of the external
power supply.
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