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

SERVICE
MANUAL
HF/VHF/UHF ALL MODE TRANSCEIVER
i706 MKªG
IC-706MK2G  99.3.11 7:31 PM  Page 1 

INTRODUCTION
This service manual describes the latest service information
for the IC-706MKIIGHF/VHF/UHF ALL MODE TRANS-
CEIVER at the time of publication.
To upgrade quality, any electrical or mechanical parts and
internal circuits are subject to change without notice or
obligation.
DANGER
NEVERconnect the transceiver to an AC outlet or to a DC
power supply that uses more than 16 V. This will ruin the
transceiver.
DO NOTexpose the transceiver to rain, snow or any liquids.
DO NOTreverse the polarities of...

TABLE OF CONTENTS
SECTION 1 SPECIFICATIONS
SECTION 2 INSIDE VIEWS
SECTION 3 CIRCUIT DESCRIPTION
3 - 1 RECEIVER CIRCUITS ................................................................................................................................ 3 - 1
3 - 2 TRANSMITTER CIRCUITS ......................................................................................................................... 3 - 4
3 - 3 PLL CIRCUITS...

nGENERAL
• Frequency coverage :
Receive 0.030 – 200.000 MHz*
430.000 – 470.000 MHz*
Transmit 1.800 –  1.999 MHz*
3.500 –  3.999 MHz*
7.000 –  7.300 MHz*
10.100 –  10.150 MHz
14.000 –  14.350 MHz
18.068 –  18.168 MHz
21.000 –  21.450 MHz
24.890 –  24.990 MHz
28.000 –  29.700 MHz
50.000 –  54.000 MHz*
144.000 – 148.000 MHz*
430.000 – 450.000 MHz*
*Depending on version.
•  Mode  : USB, LSB, CW, RTTY (FSK), AM, FM,
WFM (WFM is for receiver only)
• Number of memory ch. : 107 (99 regular, 6 scan edges,1 call)...

Predrive amplifier
(Q101: 2SK2854) HPF board D/A converter
(IC2201: M62352GP)
Á
PA AND PLL UNITS
FILTER board
MAIN CPU clock
(X2161: CR-636)
MAIN CPU *
(IC 2001: HD6433337YA56F)
MAIN board
3rd IF filter for FM *
(FI791: SFPC455E-TC01)
MIC amplifier
(IC931: µPC5023GS-077-E1)
AF selector switch *
(IC861: BU4052BCFV-E2)
Tx FM PLL IC *
(IC1011: LC7153M-TLM) Balanced modulator *
(IC1041: NJM1496V) Discriminator 
(X791: CDB455CX24)
FM IF IC *
(IC791: TA31136FN) RX preamplifier
(IC151: µPC1658G)
1st mixer...

3-1 RECEIVER CIRCUITS
3-1-1 HF/50 MHz RF CIRCUIT
(FILTER, MAIN AND HPF BOARDS)
HF/50 MHz RF filters pass only the desired band signals
and suppress any undesired band signals. The HF/50 MHz
RF circuit has 7 low-pass filters and 8 high-pass filters for
specified band use.
HF/50 MHz RF signals from the [ANT1] connector, pass
through one of 7 low-pass filters as below, the transmit/
receive switching relay (FILTER board; RL1) and low-pass
filter (FILTER board; L1, L2, C1–C5), and are then applied
to the...

3-1-3 PREAMPLIFIER CIRCUIT (MAIN BOARD)
The preamplifier circuit in the IC-706MKIIG has approx.
15dB gain over a wide-band frequency range.
When the preamplifier is turned ON, the signals from the RF
circuit are applied to the preamplifier (IC151) via D2182.
Amplified or bypassed signals are applied to the 1st mixer
circuit (D271).
3-1-4 1ST MIXER CIRCUIT (MAIN BOARD)
The 1st mixer circuit mixes the receive signals with the 1st
LO signal to convert the receive signal frequencies to a 69
or 70.7 MHz 1st...

3 - 3
3-1-9 IF SHIFT CIRCUIT (MAIN BOARD)
The IF shift circuit shifts the center frequency of IF signals to
electronically shift the center frequency.
The IF shift circuit shifts the 1st LO and BFO within ±1.2 kHz
in SSB/CW/RTTY modes or ±250 Hz in CW-N/RTTY-N
modes. As a result, the 2nd IF (also 1st IF) is shifted from
the center frequency of the 2nd IF filter (FI671, FI681 or
optional IF filters). This means 2nd IF signals do not pass
through the center of the 2nd IF filter. Therefore, the higher
or...

3 - 4
3-1-14 AF SELECTOR SWITCH (MAIN BOARD)
The AF signals from one of the detector circuits are applied
to the AF selector switch (IC861). IC861 consists of dual 4-
channel analog switches which are selected with a mode
signal and the squelch control signal.
3-1-15 AF AMPLIFIER CIRCUIT (PLL UNIT)
The AF amplifier amplifies the demodulated signal to a suit-
able driving level for the speaker.
The AF signals from the AF selector switch (MAIN board;
IC861) are applied to the PLL unit via the “AFI” signal...

3 - 5
3-2-4 FM MODULATION CIRCUIT (MAIN BOARD)
The microphone signals from Q961 are applied to the limiter
amplifier (IC981a) and the splatter filter (IC981b). The 1750
Hz European tone signal from the main CPU (IC2001 pin
40) is also applied to IC981a pin 2 for European repeaters.
The sub-audible tone signal (67.0–254.1 Hz) from the main
CPU (IC2001 pin 37) is also applied to IC981b pin 5 for
repeater use.
The resulting signals are applied to the VCO circuit (Q1011,
D1012) via R1002 to change the...