Icom Ic706Mk2g Hf/Vhf/Uhf All Mode Tranciever Service Manual

3 - 6 The “FOR”, “VFOR” and “UFOR” voltages are combined to
the “FORL” voltage and then applied to IC1091b (pin 6). The
“POCV” voltage from the D/A converter (IC2201, pin 3),
determined by the RF power setting, is applied to IC1091b
(pin 5) as the reference voltage.
When the “FORL” voltage exceeds the “POCV” voltage, ALC
bias voltage from IC1091a (pin 1) controls the PIN diodes
(D521, D522, D572, D573) using Q1092. This adjusts the
output power to the level determined by the RF power set-
ting until the...

3 - 7
3-3-3 2ND LO AND REFERENCE OSCILLATOR
CIRCUITS
The reference oscillator (X621, Q621) generates a 30.0
MHz frequency used for the 1st LO and BFO circuits as a
system clock and for the 2nd LO signal.
The oscillated signal is amplified at the buffer amplifier
(Q661), and is doubled at Q681 and the 60 MHz frequency
is picked up at the bandpass filter (L681, L682). The 60 MHz
signal is applied to the MAIN board as a 2nd LO signal.
3-3-4 BFO CIRCUIT
The DDS IC (IC901) generates a 10-bit digital signal....

• BFO frequency
IF shift: Center, RTTY: Normal polarity
3-4 LOGIC CIRCUITS
3-4-1 BAND SELECTION DATA
(MAIN BOARD AND PLL UNIT)
To select the correct RF low-pass filter, high-pass filter and
VCOs on the PLL unit, the CPU outputs the following band
selection data from the I/O expander (MAIN board; IC2231,
IC2232), the D/A converter (MAIN board; IC2201) or DDS IC
(PLL unit; IC101) depending on the display frequency.
The D/A convertor output from IC2201 (pin 18) is doubled at
IC891d to obtain the band...

40
41
42
43
44
45
46
48
49–51
52
53
54
55
61
62
63
71
74
75
78
79Outputs 1750 Hz European tone sig-
nal.
Outputs a strobe signal for the option-
al UT-102 (Voice synthesizer unit).
Outputs serial data for the I/O
expanders, optional AT-180/UT-102.
Outputs a clock signal for the I/O
expanders, optional AT-180/ UT-102.
Outputs a strobe signal for the I/O
expander ICs (IC2231, IC2232).
Outputs a strobe signal for the I/O
expander ICs (IC2221, IC2222).
Outputs a strobe signal for the D/A
converter IC...

4-1 PREPARATION BEFORE SARVICING
nREQUIRED TEST EQUIPMENT
DC power supply
RF power meter
(terminated type)
Frequency counter
RF voltmeter
Standard signal 
generator (SSG)
FM deviation meter
Modulation analyzerDistortion meter
Oscilloscope
Digital multimeter
AC millivoltmeter
DC voltmeter
DC ammeter
Audio generator
Spectram analyzer
Attenuator
External speaker
EQUIPMENT GREDE AND RANGE EQUIPMENT GREDE AND RENGE
4 - 1
SECTION 4 ADJUSTMENT PROCEDURES
Output voltage : 13.8 V DC
Current capacity : 30 A or...

4-2 PLL ADJUSTMENTS
4 - 2
REFERENCE
FREQUENCY
REFERENCE
LOOP LOCK
VOLTAGE
MAIN LOOP
LOCK 
VOLTAGE
ADJUSTMENT
ADJUSTMENT ADJUSTMENT CONDITIONMEASUREMENT
VALUEPOINT
UNIT LOCATION UNIT ADJUST
1
2
1
1
2
3• Display frequency: Any
• L623 (PLL unit) : Center
• Receiving
• Display frequency: 0.0300 MHz
• Mode : USB
• Receiving
• Display frequency
: 128.99999 MHz
• Mode : USB
• Receiving
• Display frequency
: 199.99999 MHz
• Mode : USB
• Receiving
• Display frequency
: 470.00000 MHz
• Mode : USB
• ReceivingPLL...

4 - 3
• MAIN UNIT • PLL AND PA UNITS
CP131
CP401Reference loop lock 
voltage check pointReference frequency 
adjustment
C4
P681 L682
L681
C335 C306
C367
Main loop lock 
voltage adjustment Main loop lock 
voltage check point Reference loop lock 
voltage adjustment
Reference frequency 
check point 2nd LO level 
adjustment
R1082
R1084
R1086
R1088
R1045 L511
L512
L562
L563
L566 R579
L623
R602 L601
Transmit total gainOutput power
adjustment
Carrier suppression
adjustment 

4 - 4
TRANSMITTER ADJUSTMENTS (continued)
FM VCO
FM
DEVIATION
RESIDUAL
AM
AM
MODULATION
CW 
CARRIER
LEVEL
ADJUSTMENT
ADJUSTMENT ADJUSTMENT CONDITIONMEASUREMENT
VALUEPOINT
UNIT LOCATION UNIT ADJUST
1
1
1
2
1
2
3
1• Display frequency: 29.10000 MHz
• Mode : FM
• [Q1 RF POWER] : H
• [M4 TON] : OFF
• Apply no signal to [MIC] connector.
• Transmitting
• Display frequency: 29.10000 MHz
• Mode : FM
• [Q1 RF POWER] : H
• [M4 TON] : OFF
• [Q2 MIC GAIN] : 5
• Connect an audio generator to
[MIC] connector and set...

4 - 5
• MAIN UNIT
R921
R1042 R1002
R999
R1080 L511
L512 CP1011
CP1041
L562
L563
L566
Residual AM
adjustment FM VCO
check point
CP921CW carrier level
check point
AM modulation
check point
AM modulation
pre-settingFM deviation
adjustment
C1022FM VCO
adjustment
AM modulation
adjustment CW carrier level
adjustment
J281 

4 - 6
TRANSMITTER ADJUSTMENTS (continued)
IDLING
CURRENT
(for drive
amplifiers)
(for final
amplifiers)
SWR
DETECTION
ADJUSTMENT
ADJUSTMENT ADJUSTMENT CONDITIONMEASUREMENT
VALUEPOINT
UNIT LOCATION UNIT ADJUST
1
2
3
4
5
1
2
3• Display frequency: 14.10000 MHz
• Mode : USB
• [Q2 MIC GAIN] : 1 (minimum)
• turn R162, R174, R175, R214,
R231 (on the PA unit) to maximum
counterclockwise position.
• Disconnect the plug from J571 on
the PA unit.
• Transmitting
• Display frequency: 145.10000 MHz
• Mode : USB
• [Q2...