Icom IC-F50 Service Manual page 10

4-3-2 VCO CIRCUIT (MAIN UNIT)
The VCO circuit contains a separate RX VCO (Q14, D19,
D20) and TX VCO (Q13, D16, D17). The oscillated signal is
amplified at the buffer amplifiers (Q10, Q12) and is then
applied to the T/R switch (D14, D15). Then the receive 1st
LO (Rx) signal is applied to the 1st mixer (Q3) and the trans-
mit (Tx) signal to the pre-drive amplifier circuit (Q9).
A portion of the signal from the buffer amplifier (Q12) is fed
back to the PLL IC (IC4, pin 8) via the buffer amplifier (Q11)
as the comparison signal.
4-4 POWER SUPPLY CIRCUIT
4-4-1 MAIN UNIT VOLTAGE LINE
LINE
VCC The voltage from the connected battery pack.
Common 5 V converted from the VCC line at the
+5 regulator circuit (IC9). The output voltage is
+5V
supplied to the fast switch (IC17), buffer ampli-
fiers (IC16, IC18) and so on.
Common 5 V converted from the VCC line at the
S5 regulator circuit (Q23–Q25). The output volt-
S5V
age is supplied to the ripple filter (Q17), PLL IC
(IC4), FRONT unit, etc.
Receive 5 V converted from the S5V line at the
R5 regulator circuit (Q22). The output voltage is
R5V supplied to the tripler (Q19), FM IF IC (IC1), IF
amplifier (Q4), VCO switch (Q15, Q16), 1st
mixer (Q3), etc.
Transmit 5 V converted from the S5V line at the
T5V T5 regulator circuit (Q21). The output voltage is
supplied to the pre-drive (Q9), APC amplifier
(IC2).
• PLL CIRCUIT
Buffer
"LVIN" signal to the CPU
(FRONT unit; IC401, pin 49)
45.9 MHz 2nd LO
signal to the FM IF IC
(IC1, pin 2)
DESCRIPTION
RX VCO
Q14, D19, D20
Q8
TX VCO
Q13, D16, D17
Loop
filter
Phase
5
detector
Programmable
divider
Tripler
2
3
1
Q19
4-4-2 FRONT UNIT VOLTAGE LINE
LINE
Same voltage as VCC line on the MAIN unit is
applied to the FRONT unit via the J401, pins 1,
VCC
2 (FRONT unit). The voltage is supplied to the
[PWR] switch controller (Q401, Q402).
Same voltage as +5V line on the MAIN unit is
applied to the FRONT unit via the J401, pin 4
CPU5
(FRONT unit). The voltage is supplied to the
CPU (IC401), reset IC (IC408), etc.
Same voltage as S5V line on the MAIN unit is
applied to the FRONT unit via the J401, pin 5
S5V
(FRONT unit). The voltage is supplied to the mic
mute circuit (IC406), etc.
Buffer
Q12
IC4 MB15A02
Programmable
Prescaler
counter
Shift register
X2
15.3 MHz
4 - 4
DESCRIPTION
D15
Buffer
to 1st mixer circuit
Q10
D14
to transmitter circuit
Buffer
Q11
LPF
8
9
SCK
10
SO
11
PLST