Pioneer KEX-70 Service Manual page 14

EX-7O/73
Local OSC circuit
Tuning Voltage
MW mode
Tuning Voltage
Qs
Fig. 20
¢ LW Circuitry (KEX-73)
Due to the PD7004 switch matrix "LW" display provides
selection to LW by the D5/K1 transistor switch Q34 and, fol-
lowing this, D5/K3 of the 5 memory stations for LW is set to
open and the stations put in the LW memory.
With MW reception, D1 and D2 turn ON, T3 is shorted in AC
terms by C9, T4 is shorted by C10; with LW reception, the
tuning inductance is such that T1 and T3 form a series and T2
and T4 forma series.
During LW reception the local oscillator's D14 turns ON and
12
Tuning Voltage
AM Mixer
Fig. 19
LW mode
AM Mixer
r C30
Qe
c3q
DIS
"| |
Fig. 21
the oscillation frequency is determined by the tuning circuit °
composed of the C36, C37, C41, C39 and D15 (variable ca-
pacitance diode) and T9 and L5 and, as with MW reception,
the signal is applied to PD7004 through the 049 VCO am-
plifier.
The LW tuning voltage is about 3 V to 7.5 V between 153 kHz
and 281 kHz to enable tracking. As far as the PLL locking
during LW reception is concerned, there is no problem as long
as tracking is enabled in an MW tuning voltage range of 0.9 to
8.8V.