Pioneer KEX-70 Service Manual page 12

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This IC also contains a circuit that attenuates the sub channel
(L—R) with the voltage applied to pin 7 of the IC.
The voltage of pin 3 of FM IC PA4007, FE IF Unit (CWE-421) is
applied to pin 7 of LA3370 and varies in proportion to ANT
input. VR4 (Tuner Control Unit) is to be adjusted to obtain
L>R and R~L separations of 5dB when ANT input is
20 dBuV.
When the level is increased from this ANT input level, the
separation is continuously improved and a separation of about
40 dB is produced at a level of 60 dBuV.
The signal meter output is applied to pin (8) and when the
e AM Tuner (KEX-70)
This is PLL synthesizer tuner using the LA1130 IC for AM
reception.
The ANT input signal is received asynchronously at Q1 and
the 50 Hz power line induction is cut out by the high-pass
filter composed of capacitor (1B1) and L1. The Q1 output
passes through the resonance circuit composed of TC1
trimmer, variable capacitance diode D3 and the T1 secondary
coil, and it enters pin 3 (RF input) of the LA1130 IC1. The RF
signal amplified by the RF amplifier inside this IC is fed out
from pin 5.
The signal passes through the resonance circuit composed of
the T3 primary coil, variable capacitance diode D6 and TC2
trimmer, and enters pin 6 of IC LA1130. The local oscillator
circuit is activated by the resonant frequency determined by
the combined capacitance of variable capacitance diode D5,
C11, C12, C71 and C105 and the T2 inductance. This oscilla-
tion voltage is impedance-converted by the 04 buffer ampli-
fier and fed into pin 11 of IC6 PD7004 as the VCO output. The
AM-PD output signal from pin 13 of 1\C6 PD7004 is turned into
DC by the 043 and 044 loop filter. The tuning voltage is
applied to the cathode side of variable capacitance diodes D3,
D5 and D6, a loop is formed and this is locked.
The oscillation voltage is fed into pin 4 of IC1 LA1130, it is
mixed inside the IC with the RF signal supplied from pin 6 and
converted into a 468 kHz IF frequency. The MIX signal fed
out from pin 8 enhances the selectivity when it passes
through pins 9 and 11. It is then amplified by the IF amplifier
© MW/LW Tuner Section (KEX-73)
In terms of constants the MW circuitry is virtually the same as
that of the conventional voltage synthesizer tuner. The ANT
input is received by the Q2 FET, and the 50 Hz power supply
induction is cut out by the capacitor (IB1) and L1 high-pass
filter. The resonance circuit composed of the T1 secondary
coil, D3 variable capacitance diode and TC1 trimmer and the
resonance circuit composed of the T2 primary coil, D5 vari-
able capacitance diode and TC2 trimmer form a double-tuned
circuit with the C6 capacitor, the selectivity is enhanced and
the image is improved. The O8 local oscillator circuit gener-
ates a signal with feedback to the T8 secondary with C30 from
the Q8 drain and the resonance circuit composed of variable
capacitance diode D15, C34, 38, 39, 41 and the T8 primary
coil. This output is amplified by VCO amplifier 049, fed into
pin (11) of PD7004, turned into DC from the AM PD output by
loop filter Q47 and Q48, the tuning voltage is then applied to
10
audio components of the stereo demodulated output low, a
high-cut circuit works and a drop of about 3 dB is marked
from the de-emphasis at 10 kHz with an ANT input level of
25 dByV.
The FM output signal fed out from pin 6 (Rch) and pin 5 (Lch)
of the LA3370 MPX IC passes through the R61/C59 (Lch) and
R60/C60 (Rch) de-emphasis circuits. It then passes through
the Q9 and Q10 active filters where the 19 kHz and 38 kHz
signals as well as other components which adversely affect
the sound quality are removed.
inside the IC between pins 9 and 11, and it enters pin 12 via
TS. The signal is sent to the detector circuit inside the IC from
pin 12. The LA1130 !C1 has a detector circuit inside but since
ascan stop circuit is configured, the detector circuit inside the
IC is not used. Instead the detection diode is connected to IC
pin 14. Asa result, the IF signal appears at this pin.
After having passed through the detection diode D9, the
signal is fed out as the AM output from pin 2 of the tuner con-
trol unit to pin 15 of the amplifier unit.
The scan stop signal is taken out from the anode side of D9, it
passes through VR1 and is amplified by the Q5, CF1 and Q6 IF
narrowband amplifier. It is + rectified by D10 and — rectified
by D11, and is applied to both ends of C30. By applying the
signal to both ends of C30, the ripple (audio) components in
the rectified output are reduced and the chance that scanning
sensitivity deviation caused by the AM modulation will be
generated, is reduced.
The rectified output is entered into the Schmitt circuit com-
posed of Q7 and O8 and the circuit's output is used as the
stop signal.
When the ANT input signal enters, a positive voltage is
formed at the + side of C30 and a positive voltage is applied
to the base of Q7. Q8 turns OFF. As a result, the Q8 collector
is set to '"H," and a positive voltage is formed at the 032
base. Once such a voltage is formed at the 032 base, Q32
turns ON, D6/K2 of IC PD7004 is energized and the scanning
operation is stopped.
the MW D3, D5 and D15 variable capacitors, a loop is formed
and locked.
The oscillation voltage passes through C12 and the T2, T4 se-
condary for injection at the O3 base, it is mixed with the input
signal, converted into a 468 kHz IF frequency, it then passes
through a 4-element ladder ceramic filter CF1 with excellent
selectivity, amplified by 04 and Q5, detected by the diode D7
and it forms the MW output. At the same time, the carrier
rectified voltage becomes a negative voitage at the anode side
of the diode, it passes through R14 and then through R11 to
the Q5 base, it is applied to the Q4 base and when the ANT
input voltage increases, the rectified negative voltage in-
creases, 05 and 04 are both taken in the cutoff direction, the
gain of Q5 and Q4 is reduced and an AGC circuit is composed
to deal with strong signal inputs.