Icom IC-756PROIII User manual

HF/50MHz ALL MODE TRANSCEIVER
SERVICE
MANUAL

U.S.A.
Europe
France
United Kingdom
Italy
Korea
Spain
#32
#33
#34
#35
#38
#39
#40
USA
EUR
FRA
UK
ITA
KOR
ESP
INTRODUCTION
This service manual describes the latest service information
for the IC-756PROIII HF/50MHz ALL MODE TRANSCEIV-
ER.
DANGER
NEVER connect the transceiver to an AC outlet or to a DC
power supply that uses more than 16 V. This will ruin the
transceiver.
DO NOT expose the transceiver to rain, snow or any liquids.
DO NOT reverse the polarities of the power supply when con-
necting the transceiver.
DO NOT apply an RF signal of more than 20 dBm (100 mW)
to the antenna connector. This could damage the transceiv-
er’s front end.
ORDERING PARTS
Be sure to include the following four points when ordering
replacement parts:
1. 10-digit order numbers
2. Component part number and name
3. Equipment model name and unit name
4. Quantity required
<SAMPLE ORDER>
1110000960 S.IC NJM4558M IC-756PROIII MAIN-A UNIT 5 pieces
8810005770 Screw BiH M3×8 ZK IC-756PROIII Top cover 10 pieces
Addresses are provided on the inside back cover for your
convenience.
REPAIR NOTES
1. Make sure a problem is internal before disassembling the
transceiver.
2. DO NOT open the transceiver until the transceiver is
disconnected from its power source.
3. DO NOT force any of the variable components. Turn
them slowly and smoothly.
4. DO NOT short any circuits or electronic parts. An insu-
lated tuning tool MUST be used for all adjustments.
5. DO NOT keep power ON for a long time when the trans-
ceiver is defective.
6. DO NOT transmit power into a signal generator or a
sweep generator.
7. ALWAYS connect a 50 dB to 60 dB attenuator between
the transceiver and a deviation meter or spectrum ana-
lyzer when using such test equipment.
8. READ the instructions of test equipment thoroughly
before connecting equipment to the transceiver.
To upgrade quality, any electrical or mechanical parts and
internal circuits are subject to change without notice or
obligation.
Icom, Icom Inc. and are registered trademarks of Icom Incorporated (Japan) in the United States, the United Kingdom,
Germany, France, Spain, Russia and/or other countries.
VER.NO. SYMBOL VERSION

TABLE OF CONTENTS
SECTION 1 SPECIFICATIONS
SECTION 2 INSIDE VIEWS
SECTION 3 CIRCUIT DESCRIPTION
SECTION 4 ADJUSTMENT PROCEDURES
SECTION 5 PARTS LIST
SECTION 6 MECHANICAL PARTS AND DISASSEMBLY
SECTION 7 SEMI-CONDUCTOR INFORMATION
SECTION 8 BOARD LAYOUTS
8 - 1 DISPLAY BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 1
8 - 2 MODE BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 3
8 - 3 PHONE BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 3
8 - 4 KEY BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 3
8 - 5 TEN-KEY BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 3
8 - 6 PBT BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 5
8 - 7 RIT BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 5
8 - 8 MIC BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 5
8 - 9 MEMORY BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 5
8 - 10 MAIN-A UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 7
8 - 11 DSP-A BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 9
8 - 12 RF-B UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 11
8 - 13 BPF-A BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 13
8 - 14 PREAMP BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 13
8 - 15 PLL UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 15
8 - 16 PA UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 17
8 - 17 FILTER-A UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 19
8 - 18 CTRL-A UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 - 21
8 - 19 TUNER-A BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8- 23
SECTION 9 BLOCK DIAGRAM
SECTION 10 VOLTAGE DIAGRAMS
10 - 1 FRONT UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 1
10 - 2 DSP-A BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 3
10 - 3 TUNER-A, MEMORY BOARDS AND CTRL-A UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 5
10 - 4 MAIN-A UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 7
10 - 5 PLL UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 12
10 - 6 PA AND FILTER-A UNITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 15
10 - 7 BPF-A, PREAMP BOARDS AND RF-B UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 17

SECTION 1 SPECIFICATIONS
1 - 1
■GENERAL
• Frequency coverage:
Receive 0.030–60.000 MHz*1, *2
Transmit 1.800–1.999 MHz*23.500–3.999 MHz*2
5.3305, 5.3465, 5.3665, 5.3715, 5.4035 MHz*3
7.000–7.300 MHz*210.100–10.150 MHz*2
14.000–14.350 MHz*218.068–18.168 MHz*2
21.000–21.450 MHz*224.890–24.990 MHz*2
28.000–29.700 MHz*250.000–54.000 MHz*2
*
1Some frequency bands are not guaranteed.
*
2Depending on version.
*
3[USA] only.
• Mode : USB, LSB, CW, RTTY, AM, FM
• Number of memory channels :
101 (99 regular, 2 scan edges)
• Antenna connector : SO-239 ×2 (50 Ω)
phono jack (RCA; 50 Ω)
• Usable temp. range: –10˚C to +50˚C (14˚F to 122˚F)
• Frequency stability : Less than ±0.5 ppm from 1 min. after
power ON.
(–10˚C to +50˚C;14˚F to 122˚F)
• Freq. resolution : 1 Hz
• Power supply requirement:
13.8 V DC ±15% (negative ground)
• Current drain :
Transmit max. power 23 A
Receive stand-by 3.0 A (typical)
max. audio 3.3 A (typical)
• Dimensions : 340(W)×111(H)×285(D) mm
(proj. not included) ;33⁄8(W)×43⁄8(H)×117⁄32(D) in
• Weight (approx.) : 9.6 kg (21 lb 3 oz)
• ACC 1 connector : 8-pin DIN connector
• ACC 2 connector : 7-pin DIN connector
• CI-V connector : 2-conductor 3.5(d) mm (1⁄8")
• Display : 5-inch (diagonal) TFT color LCD
■TRANSMITTER
• Output power :
SSB/CW/RTTY/FM 5–100 W
AM 5–40 W
• Modulation system :
SSB PSN modulation
AM Low power modulation
FM Phase modulation
• Spurious emission : Less than –50 dB (HF bands)
Less than –60 dB (50 MHz band)
• Carrier suppression: More than 40 dB
• Unwanted sideband suppression:
More than 55 dB
• TX variable range : ±9.999 kHz
• Mic. connector : 8-pin connector (600 Ω)
• ELE-KEY connector: 3-conductor 6.35(d) mm (1⁄4")
• KEY connector : 3-conductor 6.35(d) mm (1⁄4")
• SEND connector : Phono jack (RCA)
• ALC connector : Phono jack (RCA)
■ RECEIVER
• Receive system : Triple-conversion
superheterodyne system
• Intermediate frequencies:
1st IF 64.455 MHz
2nd IF 455 kHz
3rd IF 36 kHz
• Sensitivity :
SSB, CW, RTTY (at 2.4 kHz bandwidth)
1.8–29.99 MHz*10.16 µV (10 dB S/N)
50.0–54.0 MHz*20.13 µV (10 dB S/N)
AM (at 6.0 kHz bandwidth)
0.5–1.799 MHz 13 µV (10 dB S/N)
1.8–29.99 MHz*12.0 µV (10 dB S/N)
50.0–54.0 MHz*21.0 µV (10 dB S/N)
FM (at 15 kHz bandwidth)
28.0–29.99 MHz*10.5 µV (12 dB SINAD)
50.0–54.0 MHz*20.32 µV (12 dB SINAD)
*
1Pre-amp 1 ON *2Pre-amp 2 ON
• Squelch sensitivity : (Pre-amp OFF)
SSB/CW/RTTY Less than 5.6 µV
FM Less than 1.0 µV
• Selectivity :
SSB/RTTY (at 2.4 kHz bandwidth)
More than 2.4 kHz/–6 dB
Less than 3.6 kHz/–60 dB
CW (at 500 Hz bandwidth)
More than 500 Hz/–6 dB
Less than 700 Hz/–60 dB
AM (at 6 kHz bandwidth)
More than 6.0 kHz/–6 dB
Less than 15.0 kHz/–60 dB
FM (at 15 kHz bandwidth)
More than 12 kHz/–6 dB
Less than 20 kHz/–60 dB
• Spurious and image rejection ratio:
More than 70 dB
(except IF through in 50 MHz band)
• RIT variable range : ±9.999 kHz
• Audio output power: More than 2.0 W at 10% distortion
(at 13.8 V DC) with an 8 Ωload
• PHONES connector: 3-conductor 6.35(d) mm (1⁄4")
• EXT SP connector : 2-conductor 3.5(d) mm (1⁄8") 8 Ω
■ANTENNA TUNER
• Matching impedance range:
HF bands 16.7 to 150 Ωunbalanced*1
50 MHz band 20 to 125 Ωunbalanced*2
*
1Less than VSWR 3:1 *2Less than VSWR 2.5:1
• Minimum operating input power:
8 W
• Tuning accuracy :VSWR 1.5:1 or less
• Insertion loss : Less than 1.0 dB
(after tuning)
All stated specifications are subject to change without notice or obligation.

5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
0
Horizontal
51015 0253035 20455055 40657075 60809095100 85105110115125 120 Vertical
MP2
30
29
2
1
to MAIN-A unit J201
J2001
GND
FMTL
GND
GND
GND
GND
DRAF
DTAF
GND
DMAF
D5VA
D5VA
D5VA
DRIF
GND
8V
8V
- 5V
- 5V
- 8V
- 8V
GND
AGC
GND
GND
GND
GND
GND
DTIF
GND
GND 1
2
29
30
to MAIN-A unit J202
J2002
GND
RTDT
CTFL
DSFR
MDAT
DSFW
MCK
NC
NC
DSDR
GND
M5V_d
GND
AGRS
GND
DSKY
MSL1
TXS
AMS
DSRS
ACKS
CALS
FMNS
MODS
DPGI
NSQO
GND
3R3V d
3R3V_d
• DSP-A BOARD (BOTTOM VIEW)
8 - 10

1-1-32, Kamiminami, Hirano-ku, Osaka 547-0003, Japan S-14110HZ-C1
C2004 Icom Inc.