Icom IC-F51, IC-F50 Power Supply Circuit, VCO Circuit Main Unit, Main Unit Voltage Line

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	DESCRIPTION
VCC	The voltage from the connected battery pack.
	Common 5 V converted from the VCC line at the
+5V	+5 regulator circuit (IC9). The output voltage is
	supplied to the fast switch (IC17), buffer ampli-
	fiers (IC16, IC18) and so on.
	Common 5 V converted from the VCC line at the
S5V	S5 regulator circuit (Q23–Q25). The output volt-
	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

4-4-2 FRONT UNIT VOLTAGE LINE

LINE	DESCRIPTION
	Same voltage as VCC line on the MAIN unit is
VCC	applied to the FRONT unit via the J401, pins 1,
	2 (FRONT unit). The voltage is supplied to the
	[PWR] switch controller (Q401, Q402).
	Same voltage as +5V line on the MAIN unit is
CPU5	applied to the FRONT unit via the J401, pin 4
	(FRONT unit). The voltage is supplied to the
	CPU (IC401), reset IC (IC408), etc.
	Same voltage as S5V line on the MAIN unit is
S5V	applied to the FRONT unit via the J401, pin 5
	(FRONT unit). The voltage is supplied to the mic
	mute circuit (IC406), etc.

			RX VCO						D15
								Buffer
								Q10
Buffer			Q14, D19, D20			Buffer			D14
	Q8		TX VCO			Q12
"LVIN" signal to the CPU
								Buffer
(FRONT unit; IC401, pin 49)
								Q11
			Q13, D16, D17
	Loop					IC4 MB15A02			LPF
	filter
		5	Phase	Programmable			Prescaler	8
			detector	counter
45.9 MHz 2nd LO			Programmable					9	SCK
						Shift register		10
									SO
signal to the FM IF IC	Tripler		divider					11
									PLST
(IC1, pin 2)
	3	2
	Q19		1			X2
					15.3 MHz

to 1st mixer circuit

to transmitter circuit

4 - 4