Block Diagram - Sony WRR-805A Service Manual

CIRCUIT DESCRIPTION
The WRR-805A is composed of the following circuit
blocks.
RF-93 Board
(1) RF Block
. RF amplifier circuit
FL101 and FL102 are the band-pass filters which
select the desired frequency bandwidth for the RF
input signal. The RF signal is then amplified by RF
amplifier (IC101).
The gain of the RF amplifier stage, including the loss
caused by the band-pass filter, is about 10 dB.
. 1st mixer and 1st IF amplifier circuit
The RF signal amplified as above is mixed with the 1st
local oscillation signal in the mixer(IC101), and mixer
outputs the 1st IF signal.
The frequency conversion is carried out as shown in
the equation below.
1st IF frequency = 1st local oscillation frequency - RF
input frequency
. 1st local signal oscillator circuit
The 1st local oscillation signal is generated by the
VCO(CP201), and the VCO is controlled by the CPU
IC(IC602) and PLL IC(IC202) on the MB-861 board.
. Other RF circuit
The 1st IF signal (150.75 MHz) is mixed with the 2nd
local oscillation signal, which is generated using X'tal
CP202 (140.05 MHz) connected 2nd mixer (Q101,102).
The 2nd IF signal is amplified by the Q103 and circuits
in IC102, and is detected to be output as an audio
signal.
The IC102 also outputs the RSSI signal, which is DC
level(voltage) that changes according to the change in
the RF input level.
WRR-805A (CE, AU)
SECTION 6

BLOCK DIAGRAM

MB-861 Board
(1) Output signal control block
There are two signal paths for the audio output signal
from the RF-93 board.
One is connected to the main signal path, and the other is
connected to the detector circuit described below.
The output from the detector is applied to the
CPU(IC602), and is used to control the muting circuit.
. Tone signal detector circuit
To detect the tone signal of 32.768 kHz, which is output
from the transmitter, is detected with the filter consisting
of the X'tal (X401, 402) and amplifier (IC403).
. Noise signal detector circuit
Noise signal are detected the amplifier (IC401) and
high-pass filter.
. Battery-tone signal detector circuit
To detect the tone signal of 32.782 kHz, which is
output from the transmitter, is detected with the filter
consisting of the X'tal (X403) and amplifier (IC403).
(2) Audio block
The audio signal is amplified by IC401, and is input to
the muting circuit (IC302).
The audio signal output from the muting circuit is
applied to the de-emphasis circuit (IC301) whose time
constant is 50 us, and the expander circuit (IC303).
Then, it is amplified by audio amplifier circuit (IC304),
and is divided into main signal path and monitor signal
path.
. Main signal path
The audio signal output from the MB-861 board is
converted to balanced output signal using the balanced
output transformer (T301).
. Monitor signal path
The audio signal branched from the main signal path is
applied to the monitor amplifier (IC305) via the level
control (RV401), and is sent to the headphones
connector.
(3) Power supply block
A synchronization-rectifier type PWM DC-DC converter
(IC501) changes the input voltage (1.8 to 3.0 V) up to the
appropriate power voltage (3.6 V) to be supplied to each
circuit.
6-1