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
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>
1110003200 S.IC TA31136FN IC-M502 MAIN UNIT 15 pieces
8810006050 Screw Icom screw E7 IC-M502 CHASSIS 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 insulated 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 analyzer 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 PORT ALLOCATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 4
SECTION 5 ADJUSTMENT PROCEDURES
5 - 1 PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 1
5 - 2 PLL ADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
1 - 1
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
6
1
⁄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 Ω load
• 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
157.275
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
SECTION 2 INSIDE VIEWS
2 - 1
2-1 IC-M502
• LOGIC UNIT
• MAIN UNIT
AF power amplifier
(IC14: LA4425A)
PLL IC
(IC2: µPD3140GS)
VCO circuit
Drive amplifier
(Q12: 2SC2954)
Power module*
(IC3: SC-1302)
1st mixer*
(Q3: 3SK166)
Reset IC
(IC15: S-80928ANMP)
System clock
(X1: CSTCC4.91MG 4.91 MHz)
Reference oscillator
(X2: CR-659 21.25 MHz)
1st IF filter
(FI1, FI2: FL-310)
2nd IF filter
(FI3: ALFY450E)
FM IF IC
(IC1: TA31136FN)
Main MPU
(IC16: MB90F583BPFV-G)
System clock
X3: DMX-26S 36.768 kHz,
X4: CR-610 7.9872 MHz
* Located under side of the point
SUB MPU
(IC1: µPD789405AGK-A30-9EU)
DIAL UNIT
SQL UNIT
VOL UNIT
LCD driver
(IC2: HD66712SA03FS)
Speaker
2 - 2
2-2 HM-127 (OPTIONAL UNIT)
• BOTTOM VIEW
• TOP VIEW
LCD
(DS1: A0119)
CPU
(IC1: µPD789405AGK-A30-9EU)
Data buffer circuit
Reset IC
(IC7: S-80928ANMP)
5V regulator
(IC5: TA78L05F)
MIC amplifier
(IC4: NJM2125F)
System clock
(X1: CSTCC4.91MG)
Dimmer circuit
8V regulator
(IC6: TA7808F)
Volume IC
(IC3: M62429FP)
AF/MIC switch
(IC9: TC4W53FU)
AF amplifier
(IC2: TA7368F)
SECTION 3 DISASSEMBLY INSTRUCTION
3 - 1
CAUTION: DISCONNECT the DC power cable from
the transceiver before performing any work on the transceiver. Otherwise, there is danger of electric shock and/or
equipment damage.
• Removing the LOGIC unit
q Unsolder 2 point C.
w Disconnect microphone connector from J1 and SQL/DIAL
connector from J3.
e Unscrew 5 screws D, and remove the LOGIC unit.
• Opening the transceiver case
q Unscrew 6 screws A, and remove the front unit.
w Unscrew 6 screws B, and remove the rear panel.
w Remove the 2 clips F.
e Disconnect microphone connector from J7 and CTRL
connector from J3 and EX-SP connector from J8 and
EX-GPS connector from J2.
r Unsolder 10 point G.
t Unscrew 5 screws H, and remove the MAIN unit.
• Remove the MAIN unit
q Unscrew 4 screws E from the shielding plate, then lift up
the shielding plate.
A
B
E
D
J1
J3
C
C
D
D
D
D
H
H
G
H
G
J2
J3
G
F
H
J7
H
G
J8
F
SECTION 4 CIRCUIT DESCRIPTION
4 - 1
4-1 RECEIVER CIRCUITS
4-1-1 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 (L23–L25, C134,
C136–C139). The signals are then applied to the RF circuit
via the antenna switching circuit (D17, L26, L27,
C141–C143).
4-1-2 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 (D1, L1, C2–C4) where the object
signals are led to the RF amplifier circuit (Q2).
The amplified signals at Q2 are applied to the 3-stage tunable bandpass filter (D2–D4, D34–D36, L2–L4, C13, C14,
L33, C16–C18, C20–C24) to suppress unwanted signals
and improve the selectivity. The signals are then applied to
the 1st mixer circuit.
D1–D4, D34–D36 employ varactor diodes, that are controlled by the PLL lock voltage, to track the band pass filters.
4-1-3 1ST MIXER AND 1ST IF CIRCUITS
The 1st mixer circuit converts the received signal into 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 pass 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 (Q3) to produce a 21.7 MHz 1st
IF signal.
The 1st IF signal is applied to a pair of crystal filters (FI1,
FI2) to suppress out-of-band signals and is then amplified at
the IF amplifier (Q4). The amplified signal is applied to the
2nd mixer circuit (IC1).
4-1-4 2ND IF AND DEMODULATOR CIRCUITS
The 2nd mixer circuit converts the 1st IF signal into 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 Q4 is applied to the 2nd mixer section
of IC1 (pin 16), and is mixed with a 21.25 MHz 2nd LO signal generated at the PLL circuit using the reference frequency (21.25 MHz) to produce a 450 kHz 2nd IF signal.
The 2nd IF signal from IC1 (pin 3) is passed through the
ceramic filter (FI3), where unwanted signals are suppressed, and is then applied to the 2nd IF (limiter) amplifier
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 (X1) for phase delay to obtain a non-adjusting circuit. The detected signal from IC1 (pin 9) is applied to the AF
circuit.
• 2nd IF and demodulator circuits
Mixer
16
Limiter
amp.
2nd IF filter
450 kHz
PLL IC
IC2
X2
21.25 MHz
X1
(21.25 MHz)
RSSI
IC1 TA31136FN
14
1st IF (21.7 MHz) from Q4
"SQLI" signal to the DC amplifier (IC20, pin 1)
11109
87 5 3
AF signal "DEMOD"
R8V
Squelch level
adjustment pot
2
17
16
Active
filter
FI3
Noise
detector
FM
detector
4 - 2
4-1-5 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 passed through the analog
switch (IC12, pins 10, 11), and are applied to the de-emphasis circuit (R118, C182). The de-emphasis circuit is an integrated circuit with frequency characteristic of –6 dB/octave.
The integrated signals are applied to the active filters (Q24,
Q25). Q24 functions as a high-pass filter to suppress
unwanted lower noise signals and Q25 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 (IC14,
pin 1). The output signal from IC14 (pin 4) drives the internal (external) speaker.
4-1-6 SQUELCH CIRCUIT
A squelch 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 adjustment pot (R33), 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 14 as the “SQLI” signal. The “SQLI” signal is amplified at the DC amplifier (IC20) and applied to the
CPU (IC16, pin 39) as the “SQL” signal. The CPU analyzes
the noise condition and outputs the “RMUTM”, “RMUTS”
signals to toggle the AF mute switches (Q26, Q27).
4-2 TRANSMITTER CIRCUITS
4-2-1 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 (IC11a) via the analog switch (IC10,
pins 11, 10). A capacitor (C214) and resistor (R147) are connected to the amplifier to obtain the pre-emphasis characteristics.
The amplified signals are applied to the IDC amplifier
(IC13a, pin 2) via the analog switch (IC12, pins 9, 8 and pins
4, 3) and are passed through the splatter filter (IC13b) to
suppress unwanted 3 kHz or higher signals. The filtered signals are then applied to the modulation circuit.
4-2-2 MODULATION CIRCUIT
The modulation circuit modulates the VCO oscillating signal
(RF signal) using the microphone audio signals.
Audio signals from the splatter filter (IC13b) pass through
the frequency deviation adjustment pot (R172) and are then
applied to the modulation circuit (D8) to change the reactance of D8, and modulate the oscillated signal at the TXVCO (Q7).
4-2-3 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 Q9 and Q10, and is
then applied to the Tx/Rx switch (D12). The transmit signal
from the Tx/Rx switch is amplified to the pre-drive (Q11) and
drive (Q12) amplifiers to obtain an approximate 200 mW signal level. The amplified signal is then applied to the RF
power amplifier (IC3).
4-2-4 POWER AMPLIFIER CIRCUIT
The power amplifier circuit amplifies the driver signal to an
output power level.
IC3 is a power module which has amplification output capabilities of about 35 W with 300 mW input. The output from
IC3 (pin 4) is passed through the antenna switching circuit
(D16) and is then applied to the antenna connector via the
low-pass filter.
4-2-5 APC CIRCUIT
The APC circuit stabilizes transmit output power.
The RF output signal from the power amplifier (IC3) is
detected at the power detector circuit (D14, D15, L21) and
is then applied to one of the differential amplifier inputs
(Q16, pin 5) via the High/Low control circuit (R84, Q17). The
applied voltage controls the differential amplifier output
(Q16, pin 2) and the bias voltage control (Q14). Thus the
APC circuit maintains a constant output power.
• APC circuit
T8
D14
D15
L21
/TMUT
VCC
HI/LO
"TXDET" signal
to the CPU
Q14
Q16
Q15
Q17
R84
Q12
Drive
amp.
RF signal
from PLL
to antenna
RF detector
circuit
APC control circuit
Power module
IC3
Q18
4 - 3
4-3 PLL CIRCUITS
4-3-1 GENERAL
The PLL circuit provides stable oscillation of the transmit frequency and receive 1st LO frequency. The PLL circuit compares the phase of the divided VCO frequency to the reference frequency. The PLL output frequency is controlled by a
crystal oscillator and the divided ratio of the programmable
divider.
IC2 is a dual PLL IC which controls both VCO circuits for Tx
and Rx, and contains a prescaler, programmable counter,
programmable divider phase detector, charge pomp and etc.
The PLL circuit, using a one chip PLL IC (IC2), directly generates the transmit frequency and receive 1st IF frequency
with VCOs. The PLL sets the divided ratio based on serial
data from the CPU and compares the phases of VCO signals with the reference oscillator frequency. The PLL IC
detects the out-of-step phase and output from pins 8 and 13
for Tx and Rx, respectively. The reference frequency (21.25
MHz) is oscillated at X2.
4-3-2 TX LOOP
The generated signal at the TX-VCO (Q7, D6–D8) enters
the PLL IC (IC2, 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 reference 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 (R252–R254, C292–C294), and is
then applied to varactor diodes (D6, D7) of the TX-VCO to
stabilize the oscillated frequency.
4-3-3 RX LOOP
The generated signal at the RX-VCO (Q8, D9, D10) enters
the PLL IC (IC2, 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 (R255–R257, C295, C296), and is
then applied to varactor diodes (D9, D10) of the RX-VCO to
stabilize the oscillated frequency. The lock voltage is also
used for the receiver circuit for the bandpass filter center frequency. The lock voltage from the loop filter is amplified at
the buffer-amplifier (Q6) and then applied to the RF circuit.
4-3-4 VCO CIRCUIT
The VCO outputs from TX-VCO (Q7) and RX-VCO (Q8) are
amplified at the buffer amplifiers (Q9 and Q10), and are then
sent to the Tx/Rx switch (D11, D12). The receive LO signal
is applied to the 1st mixer circuit (Q3) through a low-pass filter, and the transmit signal is applied to the pre-drive amplifier (Q11). A portion of the VCO output is reapplied to the
PLL IC (IC2, pin 2 or pin 13) via the buffer amplifier (Q5).
• PLL circuit
Loop
filter
Loop
filter
X2
21.25 MHz
Shift register/
data latch
IC2 (PLL IC)
Prescaler
Phase
detector
Programmable
counter
Prescaler
Phase
detector
Programmable
counter
Programmable
divider
3
4
5
2
8
19
13
PSTB
CK
DATA
21.25 MHz signal
to the FM IF IC
Buffer
Buffer
Buffer
Q10
Q5
Q9
to transmitter circuit
to 1st mixer circuit
D11
D12
17
16
Q7, D6–D8
TX-VCO
Q8, D9, D10
RX-VCO
4 - 4
4-4 DSC CIRCUITS (DSC UNIT)
4-4-1 DSC ENCODE CIRCUIT
The DSC signal created at CPU (IC16), is passed through
the buffer amplifier (Q33) and applied to the analog switch
(IC12, pin 1). The analog switch (IC12) is a modulation
switch that switches between microphone audio signal and
DSC signal.
4-4-2 DSC DECODE CIRCUT
The AF signals from FM IF IC (IC1, pin 9) are filtered at the
bandpass filter (IC4) with +18 dB/octave characteristics.
IC4b functions as a low-pass filter to suppress unwanted
higher noise signals and IC4a functions as a high-pass filter
to suppress lower noise signals. The filtered signals are converted analog signals into digital signals at DSC decoder IC
(IC5), and are then applied to the CPU (IC16) after shaping
waveform at IC6.
4-5 POWER SUPPLY CIRCUITS
4-5-1 VOLTAGE LINE (MAIN UNIT)
4-6 LOGIC CIRCUITS
4-6-1 MAIN UNIT
• MPU
IC16 is a 16 bit multifunction micro-computer and contains
FLASH memory, serial I/O, timer, A/D converter, D/A converter, programmable I/O, ROM and RAM.
• SYSTEM CLOCK CIRCUIT
X3, X4 are crystal oscillators and oscillate 7.9872 MHz and
32.768 kHz system clocks for the MPU (IC16) respectively.
• RESET CIRCUIT
IC15 is a reset IC. When turn power ON, IC15 outputs a
reset signal (“LOW” pulse) to MPU (IC16, pin 75).
• LOW BATTERY DETECTOR
VCC voltage is divided by R204, R205 and is applied to the
low battery detector section in the MPU (IC16, pin 42).
4-6-2 LOGIC UNIT
• CPU
IC1 is an 8 bit single chip micro-computer and contains LCD
driver, serial I/O, timer, A/D converter, programmable I/O,
ROM and RAM.
• SYSTEM CLOCK CIRCUIT
X1 is a ceramic oscillator and oscillates a 4.91 MHz system
clock for the CPU (IC1).
• LCD DRIVER
IC2 is a LCD driver for a dot matrix LCD.
• DIMMER CIRCUIT
CPU (IC1) and Q2, Q3, Q8 are dimmer circuit and control
the LCD backlight (LED).
• CONTRAST CIRCUIT
CPU (IC1) and Q1, Q4 are contrast circuit and control the 8
step display contrast.
4-7 PORT ALLOCATIONS
4-7-1 SUB CPU (LOGIC unit; IC1)
LINE
HV
HVS
VCC
8V
+5V
T8
R8
DESCRIPTION
The voltage from the connected DC power supply.
Same voltage as the HV line which is passed
through the [PWR] switch (LOGIC unit; S1).
Same voltage as the HVS line which is passed
through the power controller (RL1).
Common 8 V converted from the VCC line at the
8V regulator circuit (IC8).
Common 5 V converted from the 8V line at the
+5V regulator circuit (IC9).
Transmit 8 V controlled by the T8 control circuit
(Q20, Q21) using the SEND signal from CPU.
Receive 8 V controlled by the R8 control circuit
(Q22, Q23) using the RCV signal from CPU. The
controlled voltage is applied to the receiver circuits.
27,
28, 29, 30
31–38
42
43
44
46
47
51, 52
54
55
58–60
61
62
63
64
75–77
78–80
LRESET,
E, RW, RS
DB7–
DB0
SCAN
CHWX
CH16
SQLV
KEYM
DIALA,
DIALB
SRXD
STXD
CONTSEG3–
CONTSEG1
DTRS
IC
DSC
HL
DIM3–
DIM1
CONDOT3–
CONDOT1
Output ports for the LCD driver (IC2)
control signals.
I/O port for the LCD driver (IC2) control
signals.
Input port for the [SCAN] key.
Input port for the [CH/WX] key.
Input port for the [16/9] key.
Input port for the squelch volume level.
Input port from the microphone (HM-
126) for remote control signal
Input ports for the [CHANNEL].
Outputs communication data for main
CPU (MAIN unit; IC16).
Input port for the communication data
from main CPU (MIAN unit; IC16).
Output port for the LCD contrast.
Input port for the [DISTRESS] key.
Input port for the [LO/DX] key.
Input port for the [DSC/ENT] key.
Input port for the [HI/LO] key.
Output LCD backlight control signal for
the dimmer circuit (Q2, Q3, Q8).
Output port for the LCD contrast.
Pin Port
Description
number name
4 - 5
4-7-2 MAIN CPU (MAIN unit; IC16)
Output port for the cloning data to the
buffer (MAIN unit; Q37).
Outputs clock signal for EEPROM
(IC17).
Outputs serial data signal for EEPROM (IC17).
Outputs select signal to the analog
switch (IC12) for the microphone audio
signal or DSC signal.
D/A output port for the ATIS/DSC
encode signal to the buffer amplifier
(Q33).
Input port from the FM IF IC (IC1) for
the squelch operation.
Input port for the connected power
supply voltage detection (low battery
indicator).
Input port for the “TX” indicator from
the power detector circuit (D14, D15).
Input port for the ATIS/DSC decode
signal.
Input port for the PLL unlock signal.
Low : While PLL is locked.
Input port for the PTT switch.
Input port for the microphone hanger
detection signal.
Low : Microphone on hook
Input port for the optional unit connection detection.
Outputs the R8 regulator (Q22, Q23)
control signal.
Low : While receiving
Outputs the AF mute switch (Q26)
control signal for main body.
Low : While squelched
Outputs the AF mute switch (Q27)
control signal for the optional remote
microphone (HM-127).
Low : While squelched
Outputs beep audio for main body.
Outputs beep audio for the optional
remote microphone (HM-127).
Input port for the reset signal.
Outputs the reset signal for sub CPU
(LOGIC unit; IC1).
CLTX
ECK
EDA
MICDSC
DSC
SQL
LBAT
TXDET
DSDEC
UNLK
PTT
HANG
OPTIN
RCV
RMUTM
RMUTS
BEEPM
BPLVM
RESET
SRESET
20
23
24
27
30
39
42
44
45
46
60
61
62
66
67
68
69
71
75
100
1
2
3
4
5
6
7
8
10
11
12
13
14
15
16
17
19
STRU
SCON
OPSTB
PSTB
CK
DATA
PTTM
PTTS
MMUTE
SMUTE
SP
HI/LO
SEND
TMUTE
SRXD
STXD
CLRX
Outputs control signal to the analog
switch (IC12) for passing through the
optional VOICE SCRAMBLER unit
(UT98 or UT-112).
Outputs ON/OFF control signal for the
optional VOICE SCRAMBLER unit
(UT-98 or UT-112).
Outputs strobe signals for the optional
VOICE SCRAMBLER unit UT-98 or
UT-112.
Outputs strobe signals to PLL IC (IC2,
pin 2).
Outputs clock signal to PLL IC (IC2,
pin 3).
Outputs clock signal to PLL IC (IC2,
pin 4).
Outputs main microphone (HM-126)
select signal to the analog switch
(IC10) while intercom operation.
Outputs optional remote microphone
(HM-127) select signal to the analog
switch (IC10) while intercom
operation.
Outputs select signal for the speaker
of main microphone (HM-126) to the
analog switch (IC10) while intercom
operation.
Outputs select signal for the speaker
of optional remote microphone (HM-
127) to the analog switch (IC10) while
intercom operation.
Outputs ON/OFF control signal for the
internal speaker to the AF mute circuit
(Q32, D23, RL2).
Low : While internal speaker is ON.
Output port for RF output power (High
or Low) select signal.
Low : While low power is selected.
Outputs the T8 regulator (Q20, Q21)
control signal.
Low : While transmitting
Outputs transmit mute signal.
High : While transmitting
Input port for the communication data
from sub CPU (LOGIC unit; IC1).
Outputs communication data for sub
CPU (LOGIC unit; IC1).
Input port for the cloning data from the
buffer (D24).
Pin Port
Description
number name
Pin Port
Description
number name
5 - 1
SECTION 5 ADJUSTMENT PROCEDURES
5-1 PREPARATION
■ REQUIRED TEST EQUIPMENT
EQUIPMENT
DC power supply
RF power meter
(terminated type)
Frequency counter
FM deviation meter
DC voltmeter
GRADE AND RANGE
Output voltage : 13.8 V DC
Current capacity : 10 A or more
Measuring range : 1–50 W
Frequency range : 100–300 MHz
Impedance : 50 Ω
SWR : Less than 1.2 : 1
Frequency range : 0.1–300 MHz
Frequency accuracy : ±1 ppm or better
Sensitivity : 100 mV or better
Frequency range : 30–300 MHz
Measuring range : 0 to ±10 kHz
Input impedance : 50 kΩ/V DC or better
EQUIPMENT
Audio generator
Standard signal
generator (SSG)
Oscilloscope
AC millivoltmeter
External speaker
Attenuator
GRADE AND RANGE
Frequency range : 300–3000 Hz
Measuring range : 1–500 mV
Frequency range : 0.1–300 MHz
Output level : 0.1 µV–32 mV
(–127 to –17 dBm)
Frequency range : DC–20 MHz
Measuring range : 0.01–20 V
Measuring range : 10 mV–10 V
Input impedance : 4 Ω
Capacity : 5 W or more
Power attenuation : 40 or 50 dB
Capacity : 50 W or more
‘‘
CONNECTIONS
to the antenna connector
Standard signal
generator
–17 to –125 dBm
(32 mV to 0.13 µV)
CAUTION:
DO NOT transmit while SSG is
connected to the antenna connector.
Frequency
counter
FM deviation
meter
Attenuator
40 dB or 50 dB
to DC cable
DC power supply
13.8 V /15 A
–
+
Black Red
RF power meter
50 Ω / 1–50 W
To external speaker
iM502
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