Pioneer KEX-70 Service Manual page 6

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