EFJohnson 764X, 761X service manual UHF Power Supply, UHF CPU IC1 Port Allocation

UHF (7640) CIRCUIT DESCRIPTION

The phase detector determines the phase differ- ence between these signals and then produces output pulses on pin 8 which are filtered by the loop filter.

This filter consists of Q34, R180, R181, and C202- C204. The output of this filter is the DC control volt- age applied to the VCO. The phase detector increases or decreases this control voltage to change the VCO frequency.

5.7.2 VCO CIRCUIT

Separate receive and transmit VCOs are used. The receive VCO consists of Q23/D20/D34 and the transmit VCO consists of Q25/D22/D33. The signal from these VCOs is amplified by buffer amplifiers Q28 and Q29 and is then applied to T/R switch D18 and D19. The VCO receive injection signal is applied to first mixer Q3, and the VCO transmit signal is applied to driver Q21. Part of the Q28 output signal is amplified by Q29 and fed back to PLL IC10, pin 2 as described in the preceding section.

5.7.3 UHF POWER SUPPLY

Line	Description
VCC	Unswitched input voltage to the transceiver.
HV	VCC supply voltage switched by Q14 and Q15.
	When the [POWER] switch is pressed, the CPU
	outputs the “PWON” control signal to this circuit
	to turn the HV supply on.
CPU5V	Common 5V supply for the CPU produced from
	the VCC supply by CPU5V regulator IC3. The
	circuit outputs this voltage regardless of the
	transceiver on-off condition.
8V	Common 8V supply produced from the HV
	supply by 8V regulator IC2.
5V	Common 5V supply produced from the HV
	supply by 5V regulator Q12/Q13.
R8	Receive 8V supply produced by R8 regulator
	Q10/Q11 using the “TXC” signal from I/O
	expander IC13.
T8	Transmit 8V supply controlled by T8 regulator
	Q8/Q9 using the “TMUT” signal from I/O
	expander IC13.

5.7.4 UHF CPU IC1 PORT ALLOCATION

Pin	Port	Description
No.	Name
1	VIN	Input port for overvoltage detection from
		the vehicle power source.
12	SCK	Outputs clock signal to EEPROM IC3,
		PLL IC10 (main unit) and expanders
		IC12, IC13 (main unit), etc.
13	SI	Input port for the data signal from
		EEPROM IC3, etc.
14	SO	Outputs data signal to EEPROM IC3, PLL
		IC10 (main unit) and expanders IC12,
		IC13 (main unit).
16	CLIN	Input port for cloning signal.
17	CLOUT	Output port for cloning signal.
18	POSW	Input for the POWER switch. Low =
		POWER switch pushed.
19	NOIS	NOIS signal input port from the FM IF
		IC1 (main unit) for noise squelch
		operation.
26	PTT	Input port for the PTT switch. Low = PTT
		switch pushed.
32	RFATT	Outputs RF attenuator control signal to the
		attenuator switch (Q1 on main unit).
		Low = Attenuator function on.
36	UNLK	Input port for PLL unlock signal from the
		PLL IC10 (main unit). High = unlock.
37	PWON	Outputs control signal for the power
		switching circuit (Q14/Q15 on main unit).
38	DIM	Outputs control signal for LCD backlight.
		Low = LCD backlight on.
39	EXTPTT	Input port for the PTT switch from exter-
		nal connector J5 (main unit). Low =
		External PTT switch on.
40	DIM	Input port for the LCD backlight control
		signal from external connector J5 (main
		unit). Low = External dimmer switch on.
41	PLST	Outputs strobe signals for PLL IC10 (main
		unit).
42	DAST	Outputs strobe signals for level controller
		IC12 (main unit).
43	EXST	Outputs strobe signals for the I/O
		expander IC13 (main unit).
45,	KS1,	Output ports for the key matrix.
46	KS2
47-	KR3-	Input ports for the key matrix
50	KR10

	November 1998
5B-11	Part No. 001-7600-001