Sony ICF-6800W - Page 15

B+ TO
COUNTER
When Q48 goes OFF, the collector potential
of Q48 goes up, to feed a charging current to C180.
Q49 goes ON by this current flow. When Q49
goes ON, Q48 goes OFF.
When Q49 goes ON, the collector voltage of
Q49 becomes close to zero volts, and so Q47 also
goes OFF, When Q47 goes OFF, the potential of
the base of Q46 rises, and Q46 also goes OFF. Asa
result, the supply of the B+ voltage to the counter
section stops.
When S7 is pressed, these functions are repeated
by Q48 and Q49 alternately. When S7 is pressed
again, Q48 and Q49 revert to their original state,
and Q46 goes ON.
In this manner, each time S7 is pressed, Q46
repeats going ON and OFF.
Function of R196
This resistor determines the bias of the base
Q48, in order that Q48 will go OFF without fail
after the RADIO switch has been switched ON.
@ negative
pulse V~
C18i i”
RI95 RI98
b”
AM
FREQUENCY
DISPLAY
| ICF-6800W
Frequency Counter
The frequency counter of the ICF-6800W
provides a digital readout of the frequency being
tuned in. Fig. 31 shows a block diagram of its
circuitry. Digital readouts are provided only during
reception of MW and SW bands.
During MW reception, the frequency of the
VFO, and during SW reception the oscillating fre-
quency of VCO1, are counted respectively.
Q25 and Q26 go ON during MW reception
and SW reception respectively, and provide frequency
readouts of either MW or SW.
The functions of each of the circuits will now
be explained.
IC7 (RF amplifier)
Provided to amplify the signals from the VFO
or VCO1 for feeding to the next stage, and has
a bandwidth ranging from several hundred kHz
to several score MHz.
IC6 (divider)
The signal that has passed through IC7 is divided
by 40 in IC6.
This is because unless the input signal of IC4
is demultiplied by 1/40, the frequency countout will
not be accomplished properly.
Fig. 30
ON in MW
VFO
Bercel
id
RF
AMP
1/4
DIVIDER
a22
ae
1C7
1C6
ON in SW
COUNTER
vCO1 OSC BUFFER
026
COUNTER
1C4 LED
10 MHz OSC 1/10 DIVIDER
050 1C8
Fig. 31
= 15—-