Icom IC-M45 Service manual
SERVICE
MANUAL
VHF MARINE TRANSCEIVER
INTRODUCTION
DANGER
This service manual describes the latest service information
for the IC-M45 VHF MARINE TRANSCEIVER at the time of
publication.
2 versions of the IC-M45 have been designed. This service
manual covers each version.
MODEL
IC-M45
VERSION
USA
USA-1
SYNBOL
BLACK
WHITE
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>
1110003490 S.IC TA31136FN IC-M45 MAIN UNIT 5 pieces
8810008660 Screw PH BO M3x8 NI IC-M45 Chassis 10 pieces
Addresses are provided on the inside back cover for your
convenience.
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 (100mW)
to the antenna connector. This could damage the transceiver's front end.
REPAIR NOTES
1. Make sure a problem is internal before disassembling
the transceiver.
2. DO NOT open the transceiver until the transceiver is dis-
connected 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 insulat-
ed turning tool MUST be used for all adjustments.
5. DO NOT keep power ON for a long time when the transceiver 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 analyzer when using such test equipment.
8. READ the instructions of test equipment thoroughly
before connecting equipment to the transceiver.
SECTION 1 SPECIFICATIONS
VHF MARINE CHANNEL LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-2
SECTION 2 DISASSEMBLY INSTRUCTIONS
SECTION 3 CIRCUIT DESCRIPTION
3-1 RECEIVER CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1
3-2 TRANSMITTER CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2
3-3 PLL CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3
3-4 POWER SUPPLY CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3
3-5 PORTALLOCATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4
SECTION 4 ADJUSTMENT PROCEDURES
4-1 PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1
4-2 PLLADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2
4-3 TRANSMITTER ADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2
4-4 RECEIVER ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2
SECTION 5 PARTS LIST
SECTION 6 MECHANICAL PARTS AND DISASSEMBLY
SECTION 7 SEMI-CONDUCTOR INFORMATION
SECTION 8 BOARD LAYOUTS
8-1 LOGIC UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-1
8-2 MAIN UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-3
SECTION 9 BLOCK DIAGRAM
SECTION 10 VOLTAGE DIAGRAM
10-1 LOGIC UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-1
10-2 MAIN UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-2
10-3 VR-AAND VR-B UNITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-3
TABLE OF CONTENTS
1 - 1
SECTION 1 SPECIFICATIONS
‘‘
GENERAL
• Frequency coverage : 156.025–157.425 MHz (Tx)
156.025–163.275 MHz (Rx)
• Mode : 16K0G3E (FM)
• Usable channels : All USA, international and Canadian channels
plus 10 weather channels*
*USA versions only
• Power supply requirement : 13.8 V DC ±15% (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 6.0 A
Receive max. audio 1.2 A
• Antenna impedance : 50 Ω
(nominal)
• Dimensions (projections not included) : 152(W)×67(H)×144(D) mm; 6(W)×25⁄8(H)×52⁄3(D) in
• Weight
(with ant., battery case and cells) : 900 g; 2 lb
‘‘
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 dB
• Adjacent channel power : 60 dB
• Residual modulation : 40 dB
• Audio harmonic distortion : Less than 10% at 70% deviation
• Audio frequency response : +1 dB to –3 dB of 6 dB octave from 300 Hz to 3000 Hz
‘‘
RECEIVER
• Receive system : Double conversion superheterodyne system
• Intermediate frequencies : 1st 30.85 MHz
2nd 450 kHz
• Sensitivity : 0.22 µV typical at 12 dB SINAD
• Squelch sensitivity : 0.22 µV typical
• Adjacent channel selectivity : 70 dB typical
• Spurious response : 70 dB typical
• Intermodulation rejection ratio : 70 dB typical
• Hum and noise : 40 dB
• Audio output power (at 13.8 V DC) : 4.0 W typical at 10% distortion with an 4 Ω load
• Audio frequency responce : +2 dB to –8 dB of –6 dB octave from 300 Hz to 3000 Hz
All stated specifications are subject to change without notice or obligation.
1 - 2
*1Low power only, *2Momentary high power, *3Receive only
NOTE: Channels 3, 21, 23, 61, 64, 81, 82 and 83 CANNOT be 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*
3
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
21
‘‘
VHF MARINE CHANNEL LIST
USA
01A
03A
05A
06
07A
08
09
10
11
12
13*
2
14
15*
2
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*
2
68
69
70*
3
71
72
INT
22
23
24
25
26
27
28
60
61
62
63
64
65
65A
66
66A
67
68
69
70*
3
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
157.275
161.925
157.325
161.975
157.375
162.025
157.425
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
2 - 1
SECTION 2 DISASSEMBLY INSTRUCTIONS
•
REMOVING THE CASE
Unscrew 4 screws, , as shown below, and slide the case
free of the chassis.
Note: When replacing the screw, 10–12 kg of torque MUST
be applied to ensure water resistance.
•
REMOVING THE MAIN UNIT
Unsolder DC cable (2 points) and antenna connector,
(3 points), as shown below.
Unscrew 2 screws, , and 7 screws, , to remove the
MAIN unit.
A
C
B
D
SECTION 3 CIRCUIT DESCRIPTION
3 - 1
3-1 RECEIVER CIRCUITS
3-1-1 ANTENNA SWITCHING CIRCUIT
The antenna switching circuit functions as a low-pass filter
while receiving and as resonator circuit while transmitting.
The circuit does not allow transmit signals to enter receiver
circuits.
Received signals enter the MAIN unit from the antenna connector and pass through the low-pass filter (L1–L3, C1–C5,
C7). The signals are then applied to the RF circuit via the
antenna switching circuit (D1, L4, L25).
3-1-2 RF CIRCUIT
The RF circuit amplifies signals within the range of frequency coverage and filters out-of-band signals.
The signals from the antenna switching circuit pass through
a tunable bandpass filter (D2, L5) where the object signals
are led to the RF amplifier circuit (Q1).
The amplified signals at Q1 are applied to the 2-stage tunable bandpass filter (D3, D4, L6, L7) to suppress unwanted
signals and improve the selectivity. The signals are then
applied to the 1st mixer circuit.
D2–D4 employ varactor diodes, that are controlled by the
PLL lock voltage, to track the band pass filters.
3-1-3 1ST MIXER AND 1ST IF CIRCUITS
The 1st mixer circuit converts the received signal to a fixed
frequency of the 1st IF signal with a 1st LO (VCO output) frequency. By changing the 1st LO frequency, only the desired
frequency will be passed through a pair of crystal filters at
the next stage of the mixer.
The signals from the RF circuit are mixed with the VCO signals at the 1st mixer circuit (Q2) to produce a 30.85 MHz 1st
IF signal.
The 1st IF signal is applied to a pair of crystal filters (FI1) to
suppress out-of-band signals and is then amplified at the IF
amplifier (Q3). The amplified signal is applied to the 2nd
mixer circuit (IC1).
3-1-4 2ND IF AND DEMODULATOR CIRCUITS
The 2nd mixer circuit converts the 1st IF signal to a 2nd IF
signal. A double superheterodyne system (which converts
receive signals twice) improves the image rejection ratio and
obtains stable receiver gain.
The FM IF IC (IC1) contains the 2nd local oscillator, 2nd
mixer, limiter amplifier, quadrature detector, and noise
detector circuits, etc.
The 1st IF signal from Q3 is applied to the 2nd mixer section
of IC1 (pin 16), and is mixed with a 30.4 MHz 2nd LO signal
generated at the PLL circuit by doubling the reference frequency (15.2 MHz) to produce a 450 kHz 2nd IF signal.
The 2nd IF signal from IC1 (pin 3) is passed through the
ceramic filter (FI2), where unwanted signals are suppressed, and is then applied to the 2nd IF and limiter amplifiers in IC1 (pin 5). The signal is applied to the FM detector
section in IC1 for demodulation into AF signals.
The FM detector circuit employs a quadrature detection
method (linear phase detection), which uses a ceramic discriminator (X2) for phase delay to obtain a non-adjusting circuit. The detected signal from IC1 (pin 9) is applied to the AF
circuit.
3-1-5 AF AMPLIFIER CIRCUIT
The AF amplifier circuit amplifies the detected signals to
drive a speaker. The AF circuit includes an AF mute circuit
for the squelch.
AF signals from IC1 (pin 9) are applied to the de-emphasis
circuit (R92, C152). The de-emphasis circuit is an integrated
circuit with frequency characteristic of –6 dB/octave.
The integrated signals are applied to the active filters (Q21,
Q22). Q21 functions as a high-pass filter to suppress
unwanted lower noise signals and Q22 functions as a lowpass filter to suppress higher noise signals.
The filtered signals are passed through the [VOLUME] control, and are then applied to the AF power amplifier (IC9, pin
1) via the analog switch (IC5, pins 4, 3). The output signal
from IC9 (pin 4) drives the internal (external) speaker.
• 2nd IF AND DEMODULATOR CIRCUITS
Mixer
16
Limiter
amp.
2nd IF filter
450 kHz
PLL IC
IC3
X1
15.2 MHz
X2
(30.4 MHz)
RSSI
IC1 TA31136F
13
1st IF (30.85 MHz)
from Q3
"SQL" signal to the CPU pin 22
11109
87 5 3
AF signal "DET"
R5
Squelch level
adjustment pot
R1 (VR-B unit)
2
17
16
Active
filter
FI2
Noise
detector
FM
detector
2
3 - 2
3-1-6 SQUELCH CIRCUIT
Asquelch circuit cuts out AF signals when no RF signals are
received. By detecting noise components in the AF signals,
the squelch circuit switches the AF mute switch.
A portion of the AF signals from the FM IF IC (IC1, pin 9)
pass through the [SQUELCH] control pot, and are then
applied to the active filter section (IC1, pin 8). The active filter section amplifies and filters noise components. The filtered signals are applied to the noise detector section and
output from pin 13 as the “SQL” signal. The “SQL” signal is
applied to the CPU (LOGIC unit; IC1, pin 22). The CPU analyzes the noise condition and outputs the RMUT signal via
the I/O expander IC (IC7) to toggle the analog switches (IC5,
pins 4, 3) as an AF mute switch.
3-1-7 WEATHER ALERT DECODER CIRCUIT
[USA version only]
When the weather alert function is activated and a 1050 Hz
alert tone from an NOAA weather radio broadcast is
received, the IC-M45 emits beep tones and indicates flashing “ALT” on the display to inform of an emergency weather
report on the air.
AF signals from the FM IF IC (IC1, pin 9) are applied to the
tone decoder (IC10, pin 3). When a 1050 Hz signal is detected, the tone decoder outputs a low level signal from pin 8
and the output signals are applied to the CPU (LOGIC unit;
IC1) to control beep tones and the “ALT” indicator.
3-2 TRANSMITTER CIRCUITS
3-2-1 MICROPHONE AMPLIFIER CIRCUIT
The microphone amplifier circuit amplifies audio signals with
+6 dB/octave pre-emphasis from the microphone to a level
needed at the modulation circuit.
The AF signals from the microphone are amplified at the
microphone amplifier (IC4). A capacitor (C135) and resistor
(R114) are connected to the amplifier to obtain the preemphasis characteristics.
The amplified signals are applied to the IDC amplifier (IC6a,
pin 2) via the analog switch (IC5, pins 8, 9) and are passed
through the splatter filter (IC6b) to suppress unwanted 3 kHz
or higher signals. The filtered signals are then applied to the
modulation circuit.
3-2-2 MODULATION CIRCUIT
The modulation circuit modulates the VCO oscillating signal
(RF signal) using the microphone audio signals.
Audio signals from the splatter filter (IC6b) pass through the
frequency deviation adjustment pot (R130) and are then
applied to the modulation circuit (D7) to change the reactance of D7, and modulate the oscillated signal at the TXVCO (Q4).
3-2-3 DRIVE AMPLIFIER CIRCUIT
The drive amplifier circuit amplifies the VCO oscillating signal to a level needed at the power amplifier.
The VCO output is buffer-amplified by Q7 and Q9, and is
then applied to the T/R switch (D9). The transmit signal from
the T/R switch is amplified to the pre-drive (Q10) and drive
(Q11) amplifiers to obtain an approximate 400 mW signal
level. The amplified signal is then applied to the RF power
amplifier (IC2).
3-2-4 POWER AMPLIFIER CIRCUIT
The power amplifier circuit amplifies the driver signal to an
output power level.
IC2 is a power module which has amplification output capabilities of about 35 W. The output from IC2 (pin 4) is passed
through the antenna switching circuit (D13) and is then
applied to the antenna connector via the low-pass filter.
3-2-5 APC CIRCUIT
The APC circuit stabilizes transmit output power.
The RF output signal from the power amplifier (IC2) is
detected at the power detector circuit (D11, D12, L22) and is
then applied to one of the differential amplifier inputs (Q13,
pin 5) via the High/Low control circuit (R70, R71, Q16). The
applied voltage controls the differential amplifier output
(Q17, pin 2) and the bias voltage control (Q12). Thus the
APC circuit maintains a constant output power.
The reflected power from the antenna connector is detected
at D12 and is then applied to the CPU. The detected voltage
increases when the antenna is mismatched, causing the
output power to be switched from High to Low to protect the
power module (IC2).
• APC circuit
T5
D11
D12
L22
TMUT
HV
HI/LO
"TXDET" signal
to the CPU
Q12
Q13
Q15
Q16
R71 R70
Q11
Drive
amp.
RF signal
from PLL
to antenna
RF detector
circuit
APC control circuit
Power module
IC2
Q14
3 - 3
3-3 PLL CIRCUITS
3-3-1 GENERAL
The PLL circuit provides stable oscillation of the transmit fre-
quency and receive 1st LO frequency. The PLL circuit com-
pares the phase of the divided VCO frequency to the refer-
ence frequency. The PLL output frequency is controlled by a
crystal oscillator and the divided ratio of the programmable
divider. IC3 is a dual PLL IC which controls both VCO cir-
cuits for Tx and Rx.
The PLL circuit , using a one chip PLL IC (IC3), directly gen-
erates the transmit frequency and receive 1st IF frequency
with VCOs. The PLL sets the divided ratio based on serial
data from the CPU on the LOGIC unit and compares the
phases of VCO signals with the reference oscillator fre-
quency. The PLL IC detects the out-of-step phase and out-
put from pins 8 and 13 for Tx and Rx, respectively. The ref-
erence frequency (15.2 MHz) is oscillated at X1.
3-3-2 TX LOOP
The generated signal at the TX-VCO (Q4, D6, D7) enters
the PLL IC (IC3, pin 2) and is divided at the programmable
divider section and is then applied to the phase detector
section.
The phase detector compares the input signal with a refer-
ence frequency, and then outputs the out-of-phase signal
(pulse-type signal) from pin 8.
The pulse-type signal is converted into DC voltage (lock
voltage) at the loop filter (R41–R43, C75–C77), and then
applied to varactor diodes (D6, D7) of the TX-VCO to stabi-
lize the oscillated frequency.
3-3-3 RX LOOP
The generated signal at the RX-VCO (Q5, D8) enters the
PLL IC (IC3, pin 19) and is divided at the programmable
divider section and is then applied to the phase detector
section.
The phase detector compares the input signal with a reference frequency, and then outputs the out-of-phase signal
(pulse-type signal) from pin 13.
The pulse-type signal is converted into DC voltage (lock
voltage) at the loop filter (R34, R37, R38, C64, C73), and
then applied to varactor diode (D8) of the RX-VCO to stabilize the oscillated frequency. The lockvoltage is also used for
the receiver circuit for the bandpass filter center frequency.
The lock voltage from the loop filter is amplified at the bufferamplifier (Q6) and then applied to the RF circuit.
3-3-4 VCO CIRCUIT
The VCO outputs from Q4 (Tx) and Q5 (Rx) are bufferamplified at Q7 and Q9, and are then sent to the T/R switch
(D9). The receive LO signal is applied to the 1st mixer circuit
(Q2) through a low-pass filter, and the transmit signal is
applied to the pre-drive amplifier (Q10). Aportion of the VCO
output is reapplied to the PLL IC (IC10, pin 2 or pin 13) via
Q8.
3-4 POWER SUPPLY CIRCUITS
• PLL circuit
Shift register
×2
Prescaler
Phase
detector
Loop
filter
Programmable
counter
Programmable
divider
X1
15.2 MHz
30.4 MHz signal
to the FM IF IC
Q4, D6, D7
TX VCO
RX VCO
Buffer
Buffer
Buffer
Q9
Q8
Q7
3
4
5
P.STB
IC3 (PLL IC)
CK
DATA
to transmitter circuit
to 1st mixer circuit
D9
17
16
8
2
Q5, D8
LINE
HV
HVS
5V
R5
T5
DESCRIPTION
The voltage from the connected DC power supply.
Same voltage as the HV line which is passed
through the [PWR] switch (VR-A unit; R1).
Common 5 V converted from the HVS line at the
5V regulator circuit (IC8).
Receive 5 V converted from the 5V line at the R5
regulator circuit (Q19, Q20). The regulated voltage is applied to the receiver circuits.
Transmit 5 V converted from the 5V line at the T5
regulator circuit (Q17, Q18).
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