Icom Ic4008a/Mk2 Uhf Fm Tranciever Service Manual

SERVICE
MANUAL
UHF FM TRANSCEIVER 
LPD FM TRANSCEIVER  

INTRODUCTION
DANGER
ORDERING  PARTS
REPAIR  NOTES
This service manual describes the latest service information
for the  at the time of publication.
NEVERconnect the transceiver to an AC outlet or to a DC
power supply that uses more than 5 V. Such a connection
could cause a fire hazard and/or electric.
DO NOTexpose the transceiver to rain, snow or any liquids.
DO NOTreverse the polarities of the power supply when
connecting the transceiver.
DO NOTapply an RF signal of more than 20 dBm (100mW)
to the...

TABLE OF CONTENTS
SECTION 1 SPECIFICATIONS
SECTION 2 INSIDE VIEWS
SECTION 3 DISASEMBLY INSTRUCTION
SECTION 4 CIRCUIT DESCRIPTION
4-1 RECEIVER CIRCUITS  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1
4-2 TRANSMITER CIRCUITS  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2
4-3 PLL CIRCUITS  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

SECTION 1 SPECIFICATIONS
1 - 1
All stated specifications are subject to change without notice or obligation.Number of channels
Type of emission
Frequency stability
Frequency resolution
Power supply requirements
(negative ground)
Current drain
Operating temperature range
Number of CTCSS frequency
Dimensions 
(proj. not included)
Weight (included 3 cells)
Output power
Modulation system
Max. freqequency deviation
Spurious emissions
Adjacent channel power
External mic.connector
Receiving system
Intermediate...

CHANNEL FREQUENCY LIST
CTCSS FREQUENCY LIST
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23433.0750
433.1000
433.1250
433.1500
433.1750
433.2000
433.2250
433.2500
433.2750
433.3000
433.3250
433.3500
433.3750
433.4000
433.4250
433.4500
433.4750
433.5000
433.5250
433.5500
433.5750
433.6000
433.625024
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46433.6500
433.6750
433.7000
433.7250
433.7500
433.7750
433.8000
433.8250
433.8500
433.8750
433.9000
433.9250
433.9500
433.9750...

SECTION 2 INSIDE VIEWS
2 - 1
•MAIN UNIT
•RF UNIT
T+3 Regurator
(Q28: 2SB798)
+3 Regurator
(IC6: S-81230SG)
R+3 Regurator
(Q18: 2SA1586)
CPU
(IC1: µPD753036GK) Audio amplifier
(IC9: NJM2070M)
EEPROM
(IC3: X24C01AS)
TOP VEIW BOTTOM VEIW
1st mixer
(Q2: 2SC4226)
PLL IC
(IC1: TB31202FN)
2nd IF filter
(Fl3: CFWM450E) 1st IF amplifier
(Q1: 2SC4215) FM IF IC
(IC2: TA31136FN)
Reference oscilletor
(X1: CR-633 21.25 MHz)
VCO circuitRF amplifier 
(Q3: 2SC5194)
1st IF filter
(Fl2: FL-298)
TOP VIEW BOTTOM VIEW 

SECTION 3 DISASEMBLY INSTRUCTIONS
3 - 1
AB
B
MAIN unit RF unit
ECD
F
H
G
•REMOVING THE REAR PANEL
Unscrew 1 screw , and 4 screws .
Remove the rear panel in the direction of the arrow.
•REMOVING THE RF UNIT
Remove 1 knob,  , and unscrew 1 nut, .
Unsolder 1 point, , and  then remove the RF unit.
•REMOVING THE MAIN UNIT
Unscrew 2 screws, .
Remove the PTT rubber, .
Unsolder 2 points, , and remove the MAIN unit. 

4 - 1
SECTION 4 CIRCUIT DESCRIPTION
4-1 RECEIVER CIRCUITS
4-1-1 ANTENNA SWITCHING CIRCUIT (RF UNIT)
Received signals from the antenna connector are passed
through the low-pass filter (L5, L6, C8–C12). The filtered sig-
nals are applied to the 
l⁄4type antenna switching circuit (D7,
D101, D102, L4, L206, C209, C210).
The antenna switching circuit functions as a low-pass filter
while receiving. However, its impedance becomes very high
while D101 and D102 are turned ON (while transmitting).
Thus transmit...

4 - 2
• PLL circuit
Shift register
PrescalerPhase
detector
Loop
filter
Programmable
counter
Programmable
dividerX1
21.25 MHzto the FM IF IC 
(IC2, pin 1)
VCOBuffer
Q7
6
7
8
STB IC1 (PLL IC)
CK
DATAto transmitter circuit
to 1st mixer circuit D2
D1
9
11 1416
Q6, D4, D5
4-1-6 SQUELCH CIRCUIT (RF AND MAIN UNITS)
(1) NOISE SQUELCH
The noise squelch circuit cuts out AF signals when no RF sig-
nals are received. By detecting noise components in the AF
signals, the squelch circuit switches the AF mute switch.
A...

4 - 3
LINE
BATT
3V
+3V
R+3
T+3DESCRIPTION
The voltage from the connected battery pack.
Common 3 V converted from the BATT line at
the 3V regulator circuit (IC6). The circuit outputs
the voltage regardless of the power ON/OFF
condition.
Common 3 V converted from the BATT line at
the +3V regulator circuit (Q25, D4).
Receive 3 V cotrolled by the R+3 regulator circuit
(Q18) using the “RXV” signal from CPU (IC1).
Transmit 3 V converted from the BATT line at the
T+3 regulator circuit (Q27, Q28, D5, etc.)...