Icom IC-M502 User manual

VHF MARINE TRANSCEIVER
iM502
SERVICE
MANUAL

INTRODUCTION
This service manual describes the latest service information
for the IC-M502 VHF MARINE TRANSCEIVER at the time of
publication
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
connecting the transceiver.
DO NOT apply an RF signal of more than 20 dBm (100 mW)
to the antenna connector. This could damage the
transceIer’s front end.
ORDERING PARTS
sure to include the following four points when ordering
acement parts:
0-digit order numbers
Component part number and name
Equipment model name and unit name
Quantity required
AMPLE ORDER>
110003200 S.IC TA31136FN IC-M502 MAIN UNIT 5 pieces
810006050 Screw Icom screw E7 IC-M502 CHASSIS 10 pieces
resses 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 40 dB to 50 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.

TABLE OF CONTENTS
SECTION 1 SPECIFICATIONS
SECTION 2 INSIDE VIEWS
2 - 1 IC-M502 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - 1
2 - 2 HM-127 (OPTIONAL UNIT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - 2
SECTION 3 DISASSEMBLY INSTRUCTION
SECTION 4 CIRCUIT DESCRIPTION
4 - 1 RECEIVER CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 1
4 - 2 TRANSMITTER CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 2
4 - 3 PLL CIRCUIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3
4 - 4 DSC CIRCUIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 4
4 - 5 POWER SUPPLY CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 4
4 - 6 LOGIC CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 4
4 - 7 PORTALLOCATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 4
SECTION 5 ADJUSTMENT PROCEDURES
5 - 1 PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 1
5 - 2 PLLADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 2
5 - 3 TRANSMITTER ADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 3
5 - 4 RECEIVER ADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 4
SECTION 6 PARTS LIST
SECTION 7 MECHANICAL PARTS
7 - 1 IC-M502 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 1
7 - 2 HM-126 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 3
7 - 3 HM-127 (OPTIONAL UNIT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 3
SECTION 8 SEMI-CONDUCTOR INFORMATION
SECTION 9 BOARD LAYOUTS
9 - 1 VOL UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 1
9 - 2 DIAL UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 1
9 - 3 SQL UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 1
9 - 4 LOGIC UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 2
9 - 5 MAIN UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 4
9 - 6 CTRL UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 6
9 - 7 PWR-CORD UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 6
9 - 8 HM-126 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 6
9 - 9 HM-127 (OPTIONAL UNIT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 6
SECTION 10 BLOCK DIAGRAM
SECTION 11 VOLTAGE DIAGRAM
11 - 1 LOGIC UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 1
11 - 2 MAIN UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 2
11 - 3 HM-127 (OPTIONAL UNIT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 4
11 - 4 HM-126 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 5

SECTION 1 SPECIFICATIONS
‘‘GENERAL
• Frequency coverage : 156.025–157.425 MHz (Tx)
156.050–163.275 MHz (Rx)
• Mode : 16K0G3E (FM)
16K0G2E (DSC)
• Usable channels : All international and USA channels
• Power supply requirement : 13.8 V DC (negative ground)
• Usable temperature range : –20˚C to +60˚C (–4 ˚F to +140˚F)
• Frequency stability : ±10 ppm (–20˚C to +60˚C; –4 ˚F to +140˚F)
• Current drain (at 13.8 V DC) : Transmit at 25 W 6.5 A
Receive max. audio 1.2 A
• Antenna connector : SO-239 (50 Ω)
• Dimensions (projections not included) : 165(W)×110(H)×109.4(D) mm
61⁄2(W) ✕411⁄32(H) ✕45⁄16(D) in
•Weight : 1130 g (2 lb 8 oz)
‘‘TRANSMITTER
•Output power (at 13.8 V DC) : High 25 W
Low 1 W
•Modulation : Variable reactance frequency modulation
•Maximum frequency deviation : ±5.0 kHz
•Spurious emissions : 70 dBc
•Adjacent channel power : 70 dB
•Residual modulation : 40 dB
•Audio harmonic distortion : Less than 10% at 60% deviation
•Audio frequency response : +1 dB to –3 dB of 6 dB octave from 300 Hz to 2500 Hz
•Microphone impedance : 600 Ω
‘‘RECEIVER
•Receive system : Double conversion superheterodyne system
•Intermediate frequencies : 1st 21.7 MHz
2nd 450 kHz
•Sensitivity : 0.32 µV (–117 dBm) at 12 dB SINAD
•Squelch sensitivity : 0.32 µV at threshhold
•Adjacent channel selectivity : 75 dB
•Spurious response : 75 dB
•Intermodulation rejection ratio : 75 dB
•Hum and noise : 40 dB
•Audio output power (at 13.8 V DC) : 3.5 W typical at 10% distortion with an 4 Ωload
•Audio frequency responce : +1 dB to –3 dB of –6 dB octave from 300 Hz to 3000 Hz
Specifications are measured in accordance with TIA/EIA-603
All stated specifications are subject to change without notice or obligation.

1 - 2
*1Low power only, *2Receive only
NOTE: Simplex channels 3, 21, 23, 61, 64, 81, 82 and 83 CANNOT be lawfully used by the general public in USA waters.
CAN
21A
22A
23
24
25
26
27
28
60
61A
62A
64
64A
65A
66A*1
67
68
69
70*2
71
72
CAN
73
74
77*1
78A
79A
80A
81A
82A
83
83A
84
85
86
87
88
CAN
01
02
03
04A
05A
06
07A
08
09
10
11
12
13*1
14
15*1
16
17*1
18A
19A
20*1
21
‘‘VHF MARINE CHANNEL LIST
USA
01A
03A
05A
06
07A
08
09
10
11
12
13*1
14
15*1
16
17*1
18A
19A
20
20A
INT
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15*1
16
17
18
19
20
21
Transmit
156.050
156.050
156.100
156.150
156.150
156.200
156.200
156.250
156.250
156.300
156.350
156.350
156.400
156.450
156.500
156.550
156.600
156.650
156.700
156.750
156.800
156.850
156.900
156.900
156.950
156.950
157.000
157.000
157.050
Receive
160.650
156.050
160.700
160.750
156.150
160.800
156.200
160.850
156.250
156.300
160.950
156.350
156.400
156.450
156.500
156.550
156.600
156.650
156.700
156.750
156.800
156.850
161.500
156.900
161.550
156.950
161.600
157.000
161.650
USA
21A
22A
23A
24
25
26
27
28
61A
63A
64A
65A
66A
67*1
68
69
70*2
71
72
INT
22
23
24
25
26
27
28
60
61
62
63
64
65
65A
66
66A
67
68
69
70*2
71
72
Transmit
157.050
157.100
157.100
157.150
157.150
157.200
157.250
157.300
157.350
157.400
156.025
156.075
156.075
156.125
156.125
156.175
156.175
156.225
156.225
156.275
156.275
156.325
156.325
156.375
156.425
156.475
156.525
156.575
156.625
Receive
157.050
161.700
157.100
161.750
157.150
161.800
161.850
161.900
161.950
162.000
160.625
160.675
156.075
160.725
156.125
160.775
156.175
160.825
156.225
160.875
156.275
160.925
156.325
156.375
156.425
156.475
156.525
156.575
156.625
USA
73
74
77*1
78A
79A
80A
81A
82A
83A
84
84A
85
85A
86
86A
87
87A
88
88A
INT
73
74
77
78
79
80
81
82
83
84
85
86
87
88
Transmit
156.675
156.725
156.875
156.925
156.925
156.975
156.975
157.025
157.025
157.075
157.075
157.125
157.125
157.175
157.175
157.225
157.225
157.275
157.275
157.325
157.325
157.375
157.375
157.425
157.425
Receive
156.675
156.725
156.875
161.525
156.925
161.575
156.975
161.625
157.025
161.675
157.075
161.725
157.125
161.775
157.175
161.825
157.225
161.875
157.27
161.92
157.32
161.97
157.37
162.02
157.42
Channel No. Frequency (MHz) Channel No. Frequency (MHz) Channel No. Frequency (MHz)
WX01
WX02
WX03
WX04
WX05
Transmit
Receive only
Receive only
Receive only
Receive only
Receive only
Receive
162.550
162.400
162.475
162.425
162.450
WX06
WX07
WX08
WX09
WX10
Transmit
Receive only
Receive only
Receive only
Receive only
Receive only
Receive
162.500
162.525
161.650
161.775
163.275
Frequency (MHz) Frequency (MHz)
Weather
channel Weather channel

SECTION 2 INSIDE VIEWS
2 - 1
2-1 IC-M502
AF power amplifier
(IC14: LA4425A)
FM IF IC
(IC1: TA31136FN)
2nd IF filter
(FI3: ALFY450E)
Main MPU
(IC16: MB90F583BPFV-G)
PLL IC
(IC2: µPD3140GS)
VCO circuit
Drive amplifier
(Q12: 2SC2954)
1st mixer*
(Q3: 3SK166)
Reset IC
(IC15: S-80928ANMP)
* Located under side of the point
Reference oscillator
(X2: CR-659 21.25 MHz)
1st IF filter
(FI1, FI2: FL-310)
Power module*
(IC3: SC-1302)
System clock
X3: DMX-26S 36.768 kHz,
X4: CR-610 7.9872 MHz
• LOGIC UNIT
stem clock
: CSTCC4.91MG 4.91 MHz)
Speaker
SUB MPU
(IC1: µPD789405AGK-A30-9EU)
LCD driver
(IC2: HD66712SA03FS)
AL UNIT
L UNIT
L UNIT
• MAIN UNIT

9 - 4
•TOP VIEW
R304
125
26
50 1
1
1
1
4
4
4
8
8
8
5
5
5
7
14
8
5175
76
100
1
8
16
9
1
1
10
20
11
4
85
for FLASH
1
2
9
10
J1
GND
TMODE
TRES
SOT0
GND
+5V
TAUX3
P01
SIN0
SCK0
19
2
to optional unit UT-98 or UT-112
10
J6
+5V
GND
OPTIN
SCON
GND GND GND
SCK
SDATA
OPSTB
MICI
DETI
MICO
DETO
W1
to VOL unit J1
GND
VOL1 VOL2
from CTRL unit J2
113
142
J3
GND
DMDA CMDA
VCC
DSCMOD
GND
MICG
ICF3
MDDA MCDA
+5V
VCC
SAFO
SMIC
from LOGIC it J
113
142
J4
HVS
MLDA
8V
GND GND
SP– SP–
HV
LMDA
VPP
SRESET
+5V
SP+ SP+
18
to HM-126 J1
J7
SPMIC
AF2
GND
MIC
MICE
HANG
PTT
AF1
EXT SP
1
2
J8 AFG
AF
12
to EXT-GPS
J2
NMEAI+
NMEAI
-
9-5 MAIN UNIT

1-1-32, K S-13710HZ-CD
© 2000 Icom Inc.