Pioneer SX-3700 Service Manual page 9

l;
Terminals S1 - 54 (pin nos. 3 -6) are used in
designating reception mode. The 2 reception
modes employed in the SX-3700 (see Table 1) are
designated by varying the combination of input
levels (H and L).
The 3 different IFs during FM
mode are required in coping with IF offset in the
IF ceramic filter stage, S3 and 54 being preset
during FM mode according to the ceramic filter
characteristics .
Although
the SX-3700 FM stage quartzJock
system is capable of locking any frequency within
the FM band, the 10kHz digit (digit in the second
decimal place) in the FM frequency display will
appear only as 5 or 0.
The frequency display FL tube also incorporates
the TUNING and SIGNAL indicators. And al-
though the segrnents (anode) for these indicators
are static driven by the corresponding drive cir-
cuits, the grid is driven according to the D3 time
division pr:lse timing, thereby placing the segments
g C = H ( A R I G H T ,
sx-37c'cl
under dynamic drive. In addition, the AM and FM
indicators in the frequency display section are lit
according to the Db timing, while the kHz and
MHz indicators are lit according to the D1 timing.
MODE
st s2 s3 s4
l F { M H z )
H H
10.73
H
L
H
't0.70
H
L
H
H
'r0.67
L H L
450k Hz
Table 1
TUNI NG Indicator Circuit
The TUNING indicator consists of a center
tuning indicator (which lighLs up when a broad-
casting station frequency is properly tuned) and
2 detuning direction indicators which indicate the
direction in which the station has been tuned away
from. The corresponding drive circuits are out-
lined in Fig. 4-7.
The TUNING
indicator is activated once the
station has been tuned to within t 100kHz of the
center frequency. This is because Q22 is tumed on
and Q21 tumed off (resulting in the detector dif-
ferential amplifier IQ19 & Q20l being tumed off
and Q14 being tumed on) by the FM muting
signal appearing at pin no.13 of the IF system IC
(PA3007-A) and passed via the Schmitt circuit
(Q15 & Q16) when the station is tuned away by
more than t 100kHz.
t,
+1,.
P R E S E T A B L E 5 - O I G I T
O E C I M A L C O U N T E R
2 2 - B l T r 1 5
R O M
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F i g . 4 . 6 D 1 . D 5 t i m e d i v i s i o n p u l s e s i g n a l s