Icom Ic-F3gt/gs Vhf Fm Transceiver Service Manual

SERVICE
MANUAL
6-9-16, Kamihigashi, Hirano-ku, Osaka, 547-0002, Japan
S-13605II-CD
© 1999 Icom Inc.
VHF FM TRANSCEIVERS 

6-9-16, Kamihigashi, Hirano-ku, Osaka 547-0002, Japan
Phone :  06 6793 5302
Fax :  06 6793 0013
Communication Equipment
Himmelgeister Str. 100, D-40225 Düsseldorf, Germany
Phone : 0211 346047 Fax : 0211 333639
URL : http://www.icomeurope.comUnit 9, Sea St., Herne Bay, Kent, CT6 8LD, U.K.
Phone : 01227 741741 Fax : 01227 741742
URL : http://www.icomuk.co.ukZac de la Plaine, Rue Brindejonc des Moulinais
BP 5804, 31505 Toulouse Cedex, France
Phone : 561 36 03 03 Fax : 561 36 03 00
URL :...

TABLE OF CONTENTS
SECTION 1 SPECIFICATIONS
SECTION 2 INSIDE VIEWS
SECTION 3 DISASSEMBLY AND OPTION INSTRUCTIONS
3-1 DISASSEMBLY INSTRUCTION  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 1
3-2 OPTIONAL UNIT INSTALLATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 2
SECTION 4 CIRCUIT DESCRIPTION
4-1 RECEIVER CIRCUITS  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

1 - 1
SECTION 1 SPECIFICATIONS 
Ô Ô
GENERAL
• Frequency coverage : 136.000–150.000 MHz
• Type of emission : 16K0F3E (W-type), 8K50F3E (N-type)
• Number of channels : 32 ch (16 channels ´2 banks: 2-BANK version), 16 ch (16 channel version)
• Power supply requirement : 7.2 V DC (negative ground; supplied battery pack)
• Current drain (approx.) : Transmit at High (5.0 W) 1.6 A
at Low (1.0 W) 700 mA
Receive rated audio 250 mA
stand-by 70 mA
• Frequency stability : ±0.0005 %
• Usable temperature range : –30˚C...

2 - 1
SECTION 2 INSIDE VIEWS
• MAIN UNIT
Power amplifier
(Q1: 2SK2974) Antenna swtching circuit
(D1, D2, D8: MA77)
TOP VIEW BOTTOM VIEW
RF amplifier
(Q12: 3SK293)
VCO circuit 1st mixer
(Q13: 3SK239A) Low-pass filter circuit
TX/RX switch
(D3, D4: MA77) Mic amplifier circuit APC
 IC3A: NJM2902V
 Q37: DTA144EU
FM IF IC
(IC2: TA31136FN(D))
CPU
(IC8: HD64738747H)
EEPROM
(IC7: HN58X2432TI)
D/A converter
(IC10: M62363FP-560C)
PLL reference oscillator
(X1: CR-664 15.3 MHz)
Crystal filter
 FI1: FL-311 [NARROW]...

3 - 1
SECTION 3 DISASSEMBLY AND OPTION INSTRUCTIONS
3-1 DISASSEMBLY INSTRUCTION
• REMOVING THE CHASSIS PANEL
1Unscrew 1 nut A, and remove 1 knob B.
2Unscrew 2 screws C.
3Take off the chassis in the direction of the arrow.
4Unplug J6 to separate front panel and chassis.
• REMOVING THE MAIN UNIT
1Remove the searing rubber.
2Unsolder 3 points D, and unscrew 1 nut E.
3Unscrew 4 screws Fand 5 screws G (silver, 2mm) to separate the chassis and the MAIN unit.
4Take off the MAIN unit in the direction of the...

3 - 2
3-2 OPTIONAL UNIT INSTALLATIONS
1Remove the option cover.
2Remove the bottom protective paper of spoge.
3Connect one of UT-96, UT-105, UT-109, UT-110, UT-111, and UT-108 optional unit J5.
4Replace the option cover to the chassis-hole.
SPONGE
Parts name : 1556 sponge
Order No. : 8930013545Option cover
Option unit
J5 

4 - 1
SECTION 4 CIRCUIT DESCRIPTION
4-1 RECEIVER CIRCUITS
4-1-1 ANTENNA SWITCHING CIRCUIT
Received signals are passed through the low-pass filter (L1,
L2, C1–C5, C8). The filtered signals are applied to the l⁄4
type antenna switching circuit (D2, D8).
The antenna switching circuit functions as a low-pass filter
while receiving. However, its impedance becomes very high
while D2 and D8 are turned ON. Thus transmit signals are
blocked from entering the receiver circuits. The antenna
switching circuit...

4 - 2
4-1-5 AF CIRCUIT
AF signals from the FM IF IC (IC2, pin 9) are applied to the
mute switch (IC4, pin 1) via the AF filter circuit (IC3b, pins 6,
7). The output signals from pin 11 are applied to the AF
power amplifier (IC5, pin 4) after being passed through the
[VOL] control (R143).
The applied AF signals are amplified at the AF power ampli-
fier circuit (IC5, pin 4) to obtain the specified audio level. The
amplified AF signals, output from pin 10, are applied to the
internal speaker (SP1) as the...

4 - 3
When the driving current is increased, input voltage of the
differential amplifier (pin 2) will be increased. In such cases,
the differential amplifier output voltage (pin 1) is decreased
to reduce the driving current.
4-3 PLL CIRCUIT
A PLL circuit provides stable oscillation of the transmit fre-
quency and receive 1st LO frequency. The PLL output com-
pares the phase of the divided VCO frequency to the refer-
ence frequency. The PLL output frequency is controlled by
the divided ratio (N-data) of a...