Pioneer KEX-70 Service Manual page 8

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.