Pioneer KEX-70 Service Manual page 10

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