Pioneer KEX-70 User manual

The photo shows the model KEX-73
) PIONEER
ORDER NO.
CRT - 254-0
CASSETTE CAR STEREO WITH AM/FM ELECTRONIC TUNER
KEX=-70
.
CASSETTE
CAR
STEREO
WITH
LW/MW/FM
ELECTRONIC
TUNER
SPECIFICATIONS
General
Power source.......... DC14.4V (10.8 ~ 15.6V allowable)
Grounding system ......... 000 cece ee eee Negative type
Dimensions (chassis)......... 180(W) x 50(H) x 150(D) mm
(Front face)........ 184(W) x 56(H) x 31(D) mm
WIG a 5:6 ores owed Selma i ewe Waid sR ehis a eva ee 2.0kg
Tone controls (bass) ......... 00.00 ce eee +10 dB (100 Hz)
(treble) ...............005 + 10dB (10 kHz)
Loudness contour........ +12 dB (100 Hz), +4 dB (10kHz)
(volume: —30 dB)
Maximum outputlevel ........... 0.0.0 .c cea eaee 200 mV
Output impedance. ......... 0... cc cece eee eae 1kQ
Tape player
WAPGy
he
ee
var
eele
wees
Compact
cassette
tape
(C-30
~
C-90)
Tape speed .... 0... cece ee eee eee one 4.76 cm/sec.
(+ 0.19 cm/sec. -0.05 cm/sec.)
Fast forward/rewind time ......... Within 120 sec. for C-60
Wow & flutter............. No more than 0.09% (WRMS)
Frequency response...... 30 ~ 20,000 Hz (+3 dB) (at meta!)
30 ~ 16,000 Hz (+3 dB) (at normal)
Stereo separation............. 000 c eee More than 40 dB
Signal-to-noise ratio ........ Dolby NR IN: More than 63 dB
(IEC-A network)
Dolby NR OUT: More than 55 dB
(IEC-A network)
KEX=73
.
FM tuner
Frequency range. ....... 2. cece ee ees 87.5 ~ 108 MHz
Usable sensitivity ............. 12 dBf (1.14V/752, mono)
50 dB quieting sensitivity ....... 17 dBf (1.94V/75Q, mono)
Alternate channel selectivity............ 70 dB (+400 kHz)
Distortion ...............- 0.3% (at 65 dBf, 1kHz, stereo)
Frequency response.............. 30 ~ 15,000 Hz (+3 dB)
Stereo separation .............0.0. 40 dB (at 65 dBf, 1kHz)
AM (MW) tuner
Frequency range ........2 cece cece aee 531 ~ 1,602 kHz)
Usable sensitivity ...... 18uV (25 dB) (S/N: 20 dB) (KEX-70)
Usable sensitivity. ... . 30yV (29.5 dB) (S/N: 20 dB) (KEX-73)
Selectivity. ........ cc ccc cece ee eee 50 dB (+9 kHz)
LW tuner (KEX-73)
Frequency range ..........0e cece eee 153 ~ 281 kHz
Usable sensitivity ............. 70uV (37 dB) (S/N: 20 dB)
SEC. i wie ier mcmesiaawianearass 50 dB (+9 kHz)
Note:
Specifications and the design are subject to possible
modification without notice due to improvements.
¢ ‘Dolby’ and the double-D symbol are trademarks of Dolby Laboratories Licensing
corporation.
¢ Noise Reduction System manufactured under license from Dolby Laboratories
Licensing Corporation.
eee
PIONEER ELECTRONIC CORPORATION 4-1, Meguro 1-Chome, Meguro-ku, Tokyo 153, Japan
PIONEER ELECTRONICS OF AMERICA 1925 €, Dominguez St. Long Beach; Calif. 30810
PIONEER ELECTRONIC (EUROPE) N.V. Luithagen-Haven 9, 2030 Antwerp, Belgium
PIONEER ELECTRONICS AUSTRALIA PTY. LTD. 178-184 Boundary Road, Braeside, Victoria 3195, Austrailia
E K © APR. 1981 Printed in Japan

EX-70/73
CONTENTS
1. PARTS LOCATION......... 0.00. cece eee eee ee 1 CAUTION
2. CIRCUIT DESCRIPTION..............2.-0--06- 1 When Handling IC PD7004 and PD2001
3. ADJUSTMENT Please Observe:
3.1 Crystal OSC Frequency Adjustment .......... 17 IC PD7004 and PD2001 (IC6 and IC5 in the tuner control
3.2 FMIF Adjustment .................--00-55 18 unit— KEX-70, 1C5 and IC4 in the tuner control unit— KEX-73)
3.3. FM Tracking Adjustment................--. 19 are C-MOS ICs of extremely low power consumption and very
3.4 FM MPX Adjustment ...............-----5 20 high input impedance. Unless handled with special care, they
3.5 FM ARC Adjustment ...............-2008- 20 could be damaged by static electricity induction. these ICs are
3.6 FM Scan (Seek) Sensitivity Check ........... 21 supplied with a shorting cap (of aluminium foil) attached.
3.7 AM IF Adjustment (KEX-70)..............5- 21 When soldering or performing other repair work, always
3.8 AM Tracking Adjustment (KEX-70)........... 22 attach this cap as shown below. Remove the cap after the
3.9 MW/LW IF Adjustment (KEX-73)............ 23 repair has been completed.
3.10 MW/LW Tracking Adjustment.............. 24 Also, this type IC must not be inserted in a polystyrene pack-
3.11 AM (MW) Scan (Seek) Sensitivity Adjustment . . 25 age for storage.
3.12 LW Scan (Seek) Sensitivity Check ........... 25
3.13 Dolby NR Law Adjustment ..............00- 25
3.14 Dolby NR Level Adjustment................. 25
4. CONNECTION DIAGRAM (KEX-70)...........5-. 29
5. SCHEMATIC CIRCUIT DIAGRAM (KEX-70) .......- 33
6. CONNECTION DIAGRAM (KEX-73)...........5-- 37
7. SCHEMATIC CIRCUIT DIAGRAM (KEX-73) ....... 41
8. CABINET EXPLODED VIEW.............--.-05- 45
9. CHASSIS EXPLODED VIEW ...............0055 46
10. PACKING METHOD .......... 0.0.0 e eee eee .. 49
11. ELECTRICAL PARTS LIST. ...........0..00000- 50
¢ Cassette Mechanism Unit
See the Service Manual CX-118FV (CRT-199) when servicing
the cassette mechanism unit.
The differences from the CX-118FV are shown below.
Exploded View (Top) Page 26
CX-118FV KEX-70, KEX-73
Key No. Description Part No. Description
24 Head CPB-063 Head
Exploded View (Bottom) Page 26
CX-118FV KEX-70, KEX-73
Description Part No. Description
Motor CXM-072 Motor

1. PARTS LOCATION °
FE IF Unit
CWE-421
KEX-70O/73
For your Parts Stock Control, the fast moving items are
indicated with the marks * * and *.
* *«: GENERALLY MOVES FASTER THAN x.
This classification shall be adjusted by each distributor
because it depends on model number, temperature, hu-
midity, etc.
FM Front End Unit
CWB-079
Amp Unit
CWK-238
Knob
* CAA-348
(Balance, Bass)
Switch Unit
CWS-104 (KEX-70)
CWS-103 (KEX-73)
Knob
% CAA-349
(Volume, Treble)
2. CIRCUIT DESCRIPTION
PB Head
Motor
*% %& CXM-072
Head
* * CPB-063
Cassette Mechanism Assy
CXC-315
Grille Unit
CXC-331 (KEX-70)
CXC-324 (KEX-73)
Button
% CAC-347 (Eject)
Button
% CAC-345 (Clock, Mono, Loc.s,
Loud, 70us, Dolby NR)
Fig. 1
LevelAdj. Buffer Attenuator Buffer Balans Volume Line T. Out
a=} + ae je He]
FM,AM
re
FM(75kHz
DEV
)400Hz
Volume
ie)
1 Level Adj Margin
-1o4
Al
aaa
Tone
Line
T.
J
-2dB
-2
tes
ete
Sh
Out
-23dBs -20,5d8s
-30
4 AM (30 % MOD.) 400Hz
-4
- Test Tape G
507) (400Hz 200nwb/m) // EQ Amp
4 +40dB
-604
Reh -7idBs
Lee
Tone : Flat
Volume : Max
Fig. 2

=> Cr 4 = ir 4c}
2.1 TAPE SECTION
e Dolby NR Circuit
The Dolby NR system functions to reduce the amount of tape
hiss and expand the dynamic range of the high frequencies. It
is able to improve the S/N ratio by 10 dB.
When the Dolby NR switch is at the OFF position, the Dolby
NR circuit functions as a flat amplifier, thereby allowing tapes
which have not been recorded with the Dolby system to be
played back.
The Dolby NR switch is set to ON when playing tapes which
have been recorded with the Dolby NR system.
REVERSE
© Equalizer Amplifier
The MB3106M dual-type IC is employed in the equalizer am-
plifier.
When the 70us switch is OFF, Q1 (Lch) and Q2 (Rch) go OFF
and the amplifier functions as a normal equalizer (3180ys
+120us).
2.2 MUTING CIRCUIT
When the switch is at OFF, + B is applied to the base of tran-
sistor O5 which then turns OFF since it is a PNP type. Since
the signal components no longer pass through the highpass
filter, the circuit functions as an ordinary flat amplifier.
When the Dolby NR switch is at ON, + B is no longer applied
to the base of transistor O5 which then turns ON. +B is ap-
plied to the Dolby NR indicator which lights. Since 05 is ON,
the highpass filter is connected to the output and the Dolby
noise reduction effect is produced.
OFF
O
| op oovey wR
SWITCH
ON
1
DOLBY NR
G tNO.
Fig. 3
When the same switch is ON, Q1 and Q2 turn ON, the 70us
equalization network is added and the amplifier functions as a
CrO2 (Metal) equalizer (3180us + 7Ous), enabling the play-
back of CrO2 tapes.
CONNECTOR
Fig. 4

All the muting operations in the KEX-70 (KEX-73) are carried
out by the output section of the amplifier unit. A line trans-
former is used in this section to achieve a high common-mode
rejection ratio (CMRR).
Muting itself is performed by shorting the secondary (output
side) of the line transformer with transistors Q11 and Q12.
Muting is operational in the following circumstances:
(a) Fast forward and rewind operations
(b) A.T.S.C. (Automatic Tape Slack Canceller) operation
(c) Scanning and seek operations
(d) When the preset button has been depressed
(e) When the up/down button has been depressed
(f) When the reception band is switched over
(g) When the tuner goes OFF
Operations (a) and (b)
A positive voltage is supplied from PD2001 from mute input
pin Y, and 014 and Q13 are turned on. When Q14 and O13 are
ON, Q11 and 012 go ON and muting is effective. D11 func-
2.3 DESCRIPTION OF DECK CONTROL
IC PD2001
The PD2001 IC makes it possible to perform fast forwarding,
rewinding and direction change operation by feather-touch
control.
With every operation a muting output signal is fed out to the
PD2001 IC before the operation and a pre-muting circuit is in-
serted.
The KP-707G is included among the models which employ the
PD2001 IC and a description of its circuitry is given in Service
Manual (CRT-249) to which reference should be made.
Fig. 5 is used for this particular description. When an input is
fed into X1 for changing from the play to fast forward mode, a
muting output is first fed out and about 33ms later a voltage
virtually equivalent to the VDD is fed out to both OF and OR.
As a result, the fast forward and rewind solenoids are at-
tracted and the fast forward mode is established. The time
during which both solenoids are attracted is about 100ms. At
KEX-70/73
tions to prevent reverse current from mute input pin Z, and
the time constants of the muting operation are determined by
R90 and C57.
Operations (c)~(f}
A positive voltage is supplied from PD7004 from mute input
pin Z, and Q13 and Q14 are turned ON. When 014 and Q13
are ON, Q11 and Q12 turn ON and muting is effective.
Operation (g)
When the tuner is switched on (same for any band position), a
voltage (approx. 13V) is supplied from mute input pin X, and
C56 is charged through R92 and D12. At this point, Q15 re-
mains in the OFF mode and muting is not effective. Once the
tuner is switched OFF, the voltage from the mute input pin X
is rapidly reduced to OV. Q15 is turned ON when the charged
C56 discharges. Once 015 goes ON, Q14 and Q13 both go
ON, ultimately resulting in Q11 and Q12 being turned ON so
that muting is effective.
the same time, input X11 is set to the hold state by the latch cir-
cuit.
Once the time during which the fast forward and rewind sole-
noids are attracted has passed, the OF output is set to a high
impedance and so the fast forward solenoid is set to the hold
state with a voltage of about 2.5V determined by R76, R77,
R79 and D14. Furthermore, the OR output is grounded and
the rewind solenoid is released since no voltage is applied to
it.
When an input is fed into X3 next (changing from fast forward
to rewind), a voltage virtually equivalent to VDD is fed out to
OR and the mode is switched to rewinding. About 100ms later
the rewind solenoid is set to the hold state by a voltage deter-
mined by R76, R78, R80 and D14, and overheating of the
solenoid is prevented.
cn
FF
SOLENOID
Fig. 5

EX-70O/73
Xt INPUT
X3 INPUT
X! -————f hanGaom _____ Input latch hold
| FF REW
XI INPUT X3- INPUT
2.4 FUNCTIONS OF PD7004 CONTROL IC
® PLL Section
The PD7004 is a control IC for PLL synthesizer tuners de-
veloped to enable FM reception at 50 kHz steps and AM re-
ception (MW, LW) at 9 kHz steps. When some of the pins of
this IC are connected via a diode (switch matrix, mentioned
later), a microprocessor is activated in line with the program
written beforehand into the IC and scan, seek, memory and
ANTENNA
v7
FM FRONT END UNIT (CWB-079)
RF MIX
Circuit Circuit
Fig. 7 shows the composition of the phase-locked loop in the
FM mode. The VCO (CWB-079 local oscillator) frequency,
fvco, is amplified by 04 of CWB-079 up to the level the 1/20-
fixed divider .PB552C IC8 can divide it, and the prescaler out-
put signal of IC8 enters pin 10 of PD7004.
The signal is then fed into the programmable divider which is
microprocessor-controlled inside PD7004 and the frequency
of the signal is divided by the required ratio. A frequency of
4.5 MHz, whcih serves as the PD7004 clock pulse (funda-
mental frequency that drives the microprocessor), is gener-
ated by crystal oscillator X1, this is divided down (1/1800) to
2.5 kHz to form the reference frequency of the phase com-
7 © Loop Filter
O
&| 1C8uPBS552C lea Programabie - Bi
Fig. 6
other control operations are performed by the 28-pin C-MOS
LSI. This is combined with the IR2403 (IC7) driver IC for the
display LED to configure the PLL synthesizer tuner.
The PLL synthesizer tuner is now described centering on the
circuitry operations of the KEX-70/E (Tuner Control Unit:
CWE-070, FE IF Unit: CWE-421).
To IF Amp , Detector
Q42, 041 Data Out
aq t/20i*SS Y
Fig. 7
parator whose phase is then digitally compared with that of
the frequency-divided signal, and the pulse centering at 2.5
kHz is fed out from pin 12 via the charge pump. The fre-
quency deviation is converted into shifting voltage from a cer-
tain DC center voltage. When the frequency is higher than the
optimum, positive pulses appear at the output and the more it
deviates, the wider pulse-width and vise versa.
This output is then fed into the loop filter (active filter com-
posed of 041 and 42), the charging and discharging of C93
and C94 are used, a DC voltage is formed and this is applied to
pin 6 of CWE-421 as the tuning voltage. The oscillation fre-
quency of the CWB-079’s local oscillator is fixed and the

phase-locked loop is then completed. This mode is now
locked and the tuning voltage—between approx. 3.0V and
8.8V—is made constant. The ANT, RF and VCO circuits are
all controlled, the reception frequency is determined and this
is held.
The above can be expressed as follows:
(fvco/20)/N = fr = 2.5 kHz
fvco= Nx 20x fr
= Nx50 kHz
This means that every time the programmable divider N
counts, the reception frequency changes in a 50 kHz step.
in the AM mode the CWM-070 IC1 local oscillator output is
amplified by O4, it enters pin 11 of PD7002, its frequency is di-
* PD7004 Specifications
FM
KEX-70/73
vided down by the programmable divider to fr = 9 kHz, phase
comparison is performed as with FM, a pulse with a frequency
of 9 kHz as the reference is fed out from pin 13, a DC voltage
is formed by the Q43 and 044 loop filter, this is supplied to the
ANT, RF and OSC block of the AM tuning circuit, the oscilla-
tion frequency is fixed and locked. The AM tuning voltage
range from 0.9V to 8.8V, with the result that the frequencies
vary within a 531 kHz to 1602 kHz range.
The related formula for the AM mode is:
fvco = Nxfr
The fr serves as the channel spaces (9 kHz) and tuning is per-
formed in 9 kHz steps. This completes the description of the
PLL section.
Mw LW
Reception frequency 87.5~%108 MHz
153281 kHz
_ 53111602 kHz
Channel space 50 kHz
UP/DOWN 1 kHz
9kHz SCAN, SEEK 9 kHz
IF offset 10.700 MHz 468 kHz 468 kHz
Phase comparison reference frequency 2.5 kHz
9 kHz 1 kHz
Input frequency 4.91~5.935 MHz
9992070 kHz 621~749 kHz
Prescaler 1/20 externally mounted
Programmable counter frequency-
division ratio N
UP/DOWN 129
Number of channels 411 120 SCAN SEEK 15
FM FRONT END UNIT
19642374
Tuning Volt
Loop D.P.C
Filter Charge Pump
Frequency
Divider |/I800
4.5MHz
Xtal OSC
Timer
Frequency Divider
For instance, when the reception frequency is 87.5 MHz, the
local oscillator frequency is 98.2 MHz, a local oscillator volt-
age of about 200 mVrms (560 mVp-p) is fed out from pin 5 of
Front End CWB-079, and this enters prescaler IC8. The mini-
mum acceptable level of this IC is 150 mVp-p and frequency
division is not performed at lower levels. The maximum level
is 1Vp-p. When the above frequency is divided (1/20), the
result is 4.910 MHz and this becomes 2.5 kHz when divided
down (1/1964) by the programmable divider (N = 1964). This
matches the reference frequency and phase comparison be-
Counter
Cc
aod
Local OSC
Programable Divider 5
N 1964 ~ 2374
Down Scan CH
Counter Seek Call
| controtiee
Key Matrix Senser
None None
111~230 621749
OSC Out
C3 |,
wPB552C
1/20
66-f
3)
Display
Circuit
RAM
Memory
Fig. 8
comes possible. After digital phase compazison, the signal
enters the loop filter via the charge pump to become a DC
voltage.
When the manual UP key is depressed once, D1/K1 are
shorted by the diode and when this is sensed by the K2 pin,
the up counter inside the IC counts up, and one is added to
the programmable divider N to make 1965, thereby the fre-
quency steps up for one channel on the frequency scale to
tune into 87.55 MHz.

EX-7O/73
In the SCAN mode, the up-counter counts up one by one
with the D3/K2 matrix, single units are added in succession to
the programmable divider N starting at 1964 and both the re-
ception frequency and the display are changed. When certain
frequencies are received, a squelch signal from the tuner
enters the control unit, transistor 032 is turned on, the D6/K2
matrix is energized and the scanning operation is stopped.
In this case, scanning is automatically started with the
PD7004 microprocessor after 5 seconds. To stop this opera-
tion, the SCAN key is depressed again. When the SEEK key is
depressed during the scanning operation, the mode is set to
“seek’’ and, just as with scanning, single units are added in
succession to the programmable divider N. Once the squelch
signal is sensed, the operation is stopped just as with scan-
ning, and this remains terminated.
MW operations are the same as those for FM but the LW
operations are slightly different.
The MW frequency band ranges from 531 kHz to 1602 kHz—a
span which can be divided by 9 (multiples of 9). This means
that if the reference frequency is made 9 kHz, the same opera-
tion as with FM can be induced simply by stepping up or
down in single units the programmable divider N.
However, the LW frequency band ranges from 155 kHz to 281
kHz—a span which cannot be divided by 9— thereby making it
necessary to make the phase comparison reference frequency
1kHz.
¢ Charge Pump and Loop Filter
P07004
Comparator
The phases of the reference frequency and the VCO fre-
quency divided by the prescaler and programmable divider are
compared by the digital phase comparator. Since the output
pulse cannot be connected directly to the active filter. The PD
‘output is fed out of the complimentary switching circuit
(charge pump} which consists of a n-channel MOS FET anda
p-channel MOS FET.
The charge pump is characterized by 3 modes:
(1) When the p-channel is OFF and n-channel ON
(2) When the p-channel is ON and n-channel OFF
(3) When the unit is floating with both p- and n-channels
OFF
However, there is currently a movement to make the fre-
quency allotment of LW broadcasting station multiples of 9,
and reception frequency band will span 153 kHz to 279 kHz. In
order to cope with this change, the PD7004 allows the fre-
quency scale from 153 kHz to 281 kHz to be scanned either up
or down in 1 kHz steps during the manual UP/ DOWN tuning
operation, and it allows a jump to be made at one end of the
band to the other end.
Example of UP operation:
279 kHz > 280 kHz > 281 kHz 153 kHz> 154 kHz
Example of DOWN operation:
155 kHz > 154 kHz-> 153 kHz > 281 kHz > 280 kHz
During the SCAN/SEEK tuning operation, the frequency
scale is moved up in 9 kHz steps from the starting frequency
and when the uppermost frequency limit of 281 kHz is ex-
ceeded, the scale is moved up again in 9 kHz steps from the
lowermost frequency of 155 kHz.
Example 1 of SCAN/SEEK operation:
263 kHz > 272 kHz > 281 kHz 155 kHz > 164 kHz
Example 2 of SCAN/SEEK operation:
295 kHz > 268 kHz > 277 kHz > 155 kHz > 164 kHz
The maximum frequency switchable by a C-MOS IC is about
7.2 MHz. This means that the FM local oscillator signal fre-
quency cannot be divided directly and that a prescaler is re-
quired to divide the frequency down to about 5 MHz previ-
ously.
Fig. 9
A plus pulse and a minus pulse are fed out onto the DC
voitage.
In mode (7), Q41 and Q42 turn OFF when the minus pulse is
fed out and the 042 collector voltage rises. Next, C93 and C94
charge, the tuning voltage increases and the reception fre-
quency moves up the scale.
In mode (2), Q41 and Q42 turn ON when the plus pulse is fed
out, and the 042 collector voltage falls. As a result, the recep-
tion frequency moves down the scale.
Mode (3) signifies that the loop is locked. However, the out-
put pulses are such that the above three modes are repeated
all the time even when the loop is locked, and the locked loop
state is maintained.

* Display Control Section
A dynamic lighting system is adopted for the PD7004 display
with the LEDs being lighted in synchronization with the D1
through D6 (PD7004 pin 28 through pin 23) digit signals. A
sweep is performed in a period of about 3 msec. The digit
signals, used to indicate the digits (D1 = 1st digit; D2: 2nd
digit), are fed out from PD7004. The LEDs employed for dis-
playing the numbers are composed of 7 segments and, with
the addition of the dot [.], the 8-segment output is fed out
from the |C, the required segments of the LED for lighting are
synchronized with the digit output and segment output and
turned on, in each case at a period speed of 3 msec, with a
sweep being performed from the highest digit to the lowest
digit.
The above process is explained using Fig. 10 D1 through D6
are active at ‘’L” and S1 through S8 are active at ’H’’. If the
description is simplified and confined to one LED, then, as in
Fig. 10, the LED lights only when the digit output is ‘“L” and
the segment output is ‘““H.”
+5.8v
Q22~ Q27
On
Display
Sn
es jy be
Fig. 10
4 => Cy 48 Va 5c}
More specifically in the above figure when digit output Dn (iC
output) is ‘’L,’’ the Q23~Q27 Darlington pnp transistors turn
ON and when the segment output Sn is ‘’H,”” IR2403 and Q37
turn ON, segment 1 of the LED lights. For instance, when the
first digit output goes to ‘‘L’”’, and segments (2) and (3) go to
“HU a "is indicated and lighting is repeated as in Fig. 12 at
a speed of 3 msec.
Distributing a signal to multiple digit lines by turns is called
dynamic lighting.
In the dynamic system, much fewer IC pins are used than with
the static lighting system where each of the segments is
lighted with a DC voltage. However, the dynamic signal
which causes the lighting is a 5Vp-p square wave and so care
must be taken lest it should not interfere RF and power supply
circuit.
The frequency, clock, band and channels are indicated by the
above method.
ea __ vdeo
ee es
ies (aeons =
J ras
Ee

EX-70O/73
e Switch Matrix
PD7004
q Ne
Ae
CH3/8
All the functions of the KEX-70/E including scanning, seek,
memory and band (display) selection are controlled by the
PD7004 by sensing its D1~D6 display signals at the pin 22
through pin 19 or key sensing inputs k1 through K4.
When changing over to AM (MW), for example, D5 and K2
¢ Scan Operation
When the SCAN key is depressed with the radio on at the FM
1 position (with Q30 and Q28 ON), PD7004 is set to the SCAN
mode and the frequency division ratio N of the programmable
divider increases one step at a time during a fixed time period.
Due to the phase-locked loop configuration the tuning voltage
also rises and the reception frequency moves up the fre-
quency scale. The absence or presence of broadcasting sta-
tions is identified by PD7004 which judges whether or not 032
has turned ON with every 1-step change, and N is stopped
Y FM Front End
CwB-079
fas tne
IF Amp
TA7302P
Stop Signal Circuit
Q5,Q6,Q7, a8
IF Amp/FM Detector Noise Suppressor
PA4007
Fig. 13
are not connected unless Q13 is turned ON. Q28 connects D4
and K1 and unless this turns ON, the radio does not come on
and the frequency is not displayed.
The nine diodes, D27 ~ D34 and D41, are designed to safe-
guard against malfunctions caused when the touch-type
switches are depressed twice.
from changing. In other words, the scanning operation can be
stopped by turning Q32 ON when a station has been picked
up.
Pin 11 of the PA4007 IC, serving as the open collector output,
is set to the open state when a station is tuned in, and 032
turns ON. When no station is tuned in, it is shorted, and 032
goes OFF. It is set to the hold state when 032 goes ON during
the seek and scan operations by virtually the same operation.
The procedure is the same for AM reception.
MPX Decoder
LA3370 AF Out
PO07004
Fig. 14