Name: Icom IC-751A
Brand: Icom
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Table of Contents3
General Specifications5
Transmitter Specifications5
Receiver Specifications6
Outside and Inside Views7
Front Panel7
Display9
Top Panel9
Rear Panel10
Main Unit View11
Logic and PLL Units View13
RF Unit View15
PA Unit View15
Block Diagram17
Circuit Description18
Receiver Circuits18
RF Circuits (RF and Connector Units)18
IF Circuits/Rf Unit18
Main Unit19
Filter Section (Main Unit)19
Noise Blanker Circuit19
Two Signal Receive Characteristics Diagram19
Notch/Detector/Agc Circuit20
FM if Amplifier and Detector Circuits20
AF Amplifier Circuits20
AGC Circuit Schematic Diagram20
Transmitter Circuits21
MIC Amplifier Circuit/Balanced Modulator Circuit/Ssb and am Transmitter if Circuits/Compressor Circuit21
S-Meter Circuit21
Squelch Circuit21
CW, RTTY Oscillation Circuits22
CW Keying Circuit22
FM Oscillator and Modulator Circuits/Bfo Circuits22
Transmitter if Amplifier Circuits22
RF Unit Block Diagram23
PBT Oscillator Circuit23
SW Sidetone Circuit23
PA Unit/Filter, Connector Units23
Monitor Circuit/Monitor Preamplifier Circuit24
ALC/APC Circuit24
Transmitter Meter Circuits24
Vox and Anti-Vox Circuits24
Power Supply Circuits/Pll Circuits25
Meter/Filter Switching Circuit25
8V Regulator Circuit/Receive/Transmit 8V (R8V) Regulator Circuit25
Power Supply Switching Circuit/Regulator Switching Timing Circuit25
Reference Frequency Oscillator and Marker Circuits26
PLL Sub-Loop Block Diagram26
Main Loop Circuits27
Pll IC27
Marker Generator Chart27
Vco28
Loop System28
Loop Filter and Mute Circuits28
In-Loop Local Oscillator Circuit/Sub-Loop28
Logic Unit29
CPU/CPU Input Control Circuit29
PLL Data29
How to Derive N-Data29
Custom IC PIN Connection Chart30
CPU PIN Connection Chart30
CPU Memory Map30
I/O Expander Circuit31
N-Data of PLL31
N-Data Output Timing Diagram31
Matrix Unit32
Y0→DB0-DB3 (Ten Key)32
Y0→DB4 (Scan Start/Stop)32
Y1→Db4 (Vfo A/B)32
Y1→DB5 (Memory Read)/Y1→Db6 (Ham/General)33
Y1→DB7 (RIT On/Off)/Y2→Db0 (Function)33
Y2→DB3 (RIT/∆TX Clear)33
Y2→Db4 (Vfo A=B)33
Matrix Unit (Cont.)34
Frequency Differences in Various Modes Chart34
Display Unit35
Matrix Unit (End)35
Display Section36
Display Data Timing Chart36
DC/DC Converter Section36
Other Circuits/Enc 1 and ENC 2 Units36
Relay Unit37
Keyer Unit37
Dot, Dash Inputs and Electronic Keyer Output37
Spd/Weight/Fan Motor Control37
Disassembly and Assembly Diagrams38
Frame Disassembly38
Front Panel Disassembly40
Front Panel (2) Disassembly42
Front Panel (3) Disassembly44
Rear Panel Disassembly46
Front Unit Connector Assembly48
Main Unit Connector Assembly Diagram50
Logic and PLL Unit Connector Assembly Diagram51
RF Unit Connector Assembly Diagram52
Filter Unit Connector Assembly Diagram52
Rear Panel Connector Assembly Diagram53
Maintenance and Adjustment54
Preparation before Servicing54
PLL Adjustment55
PLL Unit View56
Frequency Adjustment57
Main Unit Illustration58
Receiver Adjustment59
Main Unit Illustraton (2)60
Receiver Adjustment (Cont.)61
Main Unit Illustration (3)62
Transmitter Adjustment63
PA Unit64
Transmitter Adjustment (Cont.)65
Main Unit Illustration (4)66
Transmitter Adjustment (Cont)67
Main Unit Illustration (5)68
Transmitter Adjustment (Continued)69
Main Unit Illustration (6)70
Board Layouts71
Front AF Unit Board Layout71
Front Marker Unit Board Layout71
Front Mode Switch Unit Board Layout71
Matrix Unit Board Layout72
Matrix Switch Unit Board Layout72
Display Unit/Keyer Unit Board Layouts73
Logic Unit Board Layout74
Main Unit Board Layout75
PLL Unit Board Layout76
RF Unit Board Layout77
PA Unit Board Layout78
PA Connector Unit/Pa Choke Unit Board Layout79
Filter Unit Board Layout80
Voltage/Circuit Diagrams81
Main Unit Circuit Diagram81
PLL Unit Circuit Diagram83
Logic Unit Circuit Diagram85
FR Unit Circuit Diagram87
Matrix Unit Circuit Diagram89
Display Unit Circuit Diagram91
PA Unit Circuit Diagram93
Filter Unit Circuit Diagram95
Keye Unit/Front Encoder Units Circuit Diagrams96
Front Unit Wiring Diagram97
IC Specifications99
Linear Ics Specifications99
Logic Ics Specifications100
Parts List105
EF Unit/Front Unit Parts List105
Display Unit Parts List106
Logic Unit Parts List108
Matrix Unit Parts List111
PLL Unit Parts List113
Main Unit Parts List116
RF Unit Parts List127
Filter Unit Parts List131
PA Unit Parts List133
Keyer Unit Parts List135
Mute Unit Parts List135
Options Installation136
Optional Filters136
Filter Reverse Switches136
FL-52A, Fl-53A, FL-63A, FL-70 Filters Installation136
Optional IC-PS35 Internal Power Supply137
FL-33 Installation137
Optional IC-EX310 Voice Synthesizer Unit138
Optional CR-64 High-Stability Crystal Unit138
Optional UT-30 Programmable Encoder Unit139
Filter Characteristics Chart139
Filter Combinations Chart140
Filter System140
Filters Diagram140
IC-751A Schematic Diagram141

Brand	Icom
Model	IC-751A
Category	Transceiver
Language	English

Icom IC-751A Service Manual

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