Kenwood KRK-18H User manual

SERVICE MANUAL
COPYRIGHT © 2018 JVC KENWOOD Corporation No.RA062<Rev.001>
2018/3
B5B-7284-00
CONTROL HEAD INTERFACE KIT, CONTROL HEAD REMOTE KIT
RA062<Rev.001>20183SERVICE MANUALB5B-7284-00
KRK-18H, KRK-19B
COPYRIGHT © 2018 JVC KENWOOD Corporation
1 PRECAUTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
2 SPECIFIC SERVICE INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
3 DISASSEMBLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11
4 ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-12
5 TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13
KRK-18H KRK-19B
This product complies with the RoHS directive for the European market. This product uses Lead Free solder.

1-2 (No.RA062<Rev.001>)
Document Copyrights
Copyright 2018 by JVC KENWOOD Corporation. All rights reserved.
No part of this manual may be reproduced, translated, distributed, or transmitted in any form or by any means, electronic,
mechanical, photocopying, recording, or otherwise, for any purpose without the prior written permission of JVC KENWOOD
Corporation.
Disclaimer
While every precaution has been taken in the preparation of this manual, JVC KENWOOD Corporation assumes no responsibility
for errors or omissions. Neither is any liability assumed for damages resulting from the use of the information contained herein.
JVC KENWOOD Corporation reserves the right to make changes to any products herein at any time for improvement purposes.

(No.RA062<Rev.001>)1-3
SECTION 1
PRECAUTION
This service manual does not describe PRECAUTION.
SECTION 2
SPECIFIC SERVICE INSTRUCTIONS
2.1 INSTALLATION
KRK-18H External View
KRK-19B External View
2.1.1 Installing the Remote Kit (KRK-18H, KRK-19B)
The KRK-18H and KRK-19B remote kit is used to remotely
operate the NX-3720/3820 series transceiver.
The KRK-18H is connected to the NX-3720/3820 operation
panel with the KCT-71 remote control cable.
The KRK-19B is connected to the NX-3720/3820 RF Deck with
the KCT-71.
Note:
The KRK-18H has the common firmware of the NX-3720/
3820.
When turning the transceiver power ON in the state from which
the firmware version of the NX-3720/3820 RF Deck and KRK-
18H is different, the firmware programming mode will start up
automatically, and “FIRM MISMATCH” is displayed on the LCD.
In this case, rewrite the newer version firmware.
The firmware is written into the NX-3720/3820 RF Deck and
KRK-18H at the same time.
2.1.2 Connection image
2.1.3 Remove the Operation panel from the transceiver
(NX-3720, NX-3820 only)
(1) Lift the two dents of the chassis on the bottom of the
transceiver with a flat-head screwdriver and remove the
panel from the chassis. (Fig.1)
Fig.1
(2) Remove the flat cable from the display unit connector of the
panel.
NX-3720/3820
RF Deck
KCT-71
Remote Control Cable
KRK-19B
KRK-18H
NX-3720/3820
Operation Panel
Flat-head Screwdriver
Flat-head Screwdriver

1-4 (No.RA062<Rev.001>)
2.1.4 Install the KRK-19B onto the NX-3720, NX-3820 RF
Deck
(1) Insert the flat cable into the interface unit (XC3-064M-00)
connector of the KRK-19B. (Fig.2)
Fig.2
Note:
The blue line of the flat cable and the flap of connector are
as same side.
After inserting, the flat cable should be locked with the
connector (flap) surely.
(2) Fit the KRK-19B with four tabs onto the front of the chassis.
(Fig.3)
Fig.3
Note:
When installing the KRK-19B onto the front of the chassis,
hold down the flat cable with your fingers to prevent it from
being caught.
2.1.5 Install the KRK-18H onto the NX-3720 or NX-3820
operation panel
(1) Insert the flat cable attached to the interface unit (XC3-
063M-00) of the KRK-18H into the display unit connector of
the panel. (Fig.4)
(The cable has been pre-inserted in the connector of the
KRK-18H.)
Fig.4
Note:
The blue line of the flat cable and the flap of connector are
as same side.
After inserting, the flat cable should be locked with the
connector (flap) surely.
2.1.6 Connect the KRK-19B and KRK-18H with the KCT-71
(1) Insert one lead wire with connector of the KCT-71 into the
connector of the KRK-19B. (Fig.5)
Fig.5
(2) Secure the cable bush as shown in the figure 6 and attach
the waterproof packing.
Note:
There is a direction to the installing of the cable bush.
Fig.6
(3) Slide the molding cover so as not to float the waterproof
packing and attach so that it is locked. (Fig.7)
Fig.7
(4) Insert the other lead wire with connector of the KCT-71 into
the connector of the KRK-18H.
(5) Attach the waterproof packing and molding cover in the
same way of step 2 and 3.
RF DECK
RF DECK
KRK-19B
KRK-19B
Connector
Connector
Connector
KRK-19B
Operation panel
Operation panel
KRK-18H
KRK-18H
Operation panel
KRK-18H
Connector
Connector
Connector
KCT-71 lead wire
With connector
KCT-71 lead wire
With connector
KRK-19B
KRK-19B
KRK-19B
Waterproof
Packing
Cable Bush
Waterproof
Packing
Cable Bush
Molding Cover
Molding Cover

(No.RA062<Rev.001>)1-5
2.2 CIRCUIT DESCRIPTION
2.2.1 Overview
The KRK-18H and KRK-19B are optional units for the NX-3720/3820 designed to separate the Mobile transceiver and Control Head
using the Remote control cable (KCT-71).
The KRK-18H is a back panel for the Control Head and controls the Control Head and it consists of power supply circuit, audio circuit,
control circuit, and external I/O circuit.
The KRK-19B is a front panel for the Mobile transceiver and it consists of power supply circuit, audio circuit, and control circuit.
These two units (KRK-18H, KRK-19B) communicate by CAN (Controller Area Network).
2.2.2 Power supply circuit
2.2.2.1 KRK-18H
SB (Switched +B Power) is provided from the Mobile transceiver when the transceiver power is on. SB is supplied to the step-down
DC/DC converter ICs (IC1, IC2), the ACC interface connector (CN2) and the Control Head interface connector (CN48).
IC1 regulates SB voltage to 5.36V (53DC) and IC2 regulates SB voltage to 3.9V (39DC). Both ICs work during SB is supplied.
53DC is the power supply for the CAN transceiver, IC6 (50D) and LEDs which are in the Control Head.
39DC is the power source of IC30, IC3, IC4, and IC5.
IC30 regulates 39DC to 1.2V (12D) and 12D supplies the power to the MPU core.
IC4 outputs 1.8V (18D) while 12D is working. 18D supplies the power to the MPU, Mobile DDR, and enables regulator ICs (IC5, IC6).
IC5 is the power supply for the MPU I/O section, the Flash memory, and the CAN transceiver. It outputs 3.3V (33D). IC5 works during
18D is operating.
IC3 is the power supply for the analog circuit. IC3 outputs 3.3V (33A). 33A works during 39DC is supplied.
18D_Flash is the power supply for the Flash memory I/O section.
After 33D ramps up, IC7 turns on, and supplies 18D_Flash from 18D.
IC6 regulates 5.36V (53DC) to 5.0V (50D) and supplies the power to the Level shift circuit.
50D is enabled while 18D is operating.

1-6 (No.RA062<Rev.001>)
Fig.1 Power supply diagram
CN1
IC1
5.3V DC/DC
Level shift for DM detect
IC2
3.9V DC/DC
IC4
1.8V DC/DC
IC30
1.2V DC/DC MPU core
MPU, Mobile DDR
IC7
Switch Flash memory
Q2
Level shift
IC5
3.3V AVR
MPU I/O, Flash memory
CAN transceiver
IC3
3.3V AVR Audio circuits
XC3-063
CAN transceiver
IC6
5V AVR
CN2
AUX Interface
Modular Interface
CN48
LEDs for backlight, indicator
LCD module, I/O Expander
LCD module
39DC
39DC
12D
12D
18D
33D
33A
18D_Flash
53DC
50D
SB
SB
18D
18D
33D
53DC
33D
18D

(No.RA062<Rev.001>)1-7
2.2.2.2 KRK-19B
54M (5.4V DC Power) is supplied from the Mobile transceiver via CN1. 54M is the power source of IC2 (CAN Transceiver) and IC3
(33A, 3.3V regulator). 33A (3.3V DC Power) is the power source of the Audio circuits.
32M (3.3V DC Power) is supplied from the Mobile transceiver via CN1. 32M is used for I/O control of IC2.
SB (Switched +B Power) is supplied from the Mobile transceiver via CN1. SB is the power source of the KRK-18H.
Fig.2 Power supply diagram
2.2.3 Audio circuit
2.2.3.1 RX Audio
The RX audio signal is controlled of the amplitude according to the volume setting and amplified by the AF power amplifier in the Mobile
transceiver. The amplified signal is going through the KRK-19B and the KRK-18H, and is connected to the speaker at the Control
Head.
2.2.3.2 TX Audio
The KRK-18H has two microphone input channels. One is connected to the Control Head (modular jack), and the other is connected
to the AUX interface connector (CN2).
These microphone signals are selected by the analog multiplexer IC (IC20), and are amplified by the microphone amplifier (IC18).
The microphone amplifier consists of the operational amplifier and AGC (Automatic Gain Control). The output signal of the microphone
amplifier is converted to the balanced microphone signal by the operational amplifier (IC13) and is supplied to the KRK-19B. The
balanced microphone signals (MIC+/-) are converted to single-end signal by IC1 on the KRK-19B. The converted signal is supplied to
the Mobile transceiver.
2.2.4 Control circuit
The control circuit consists of the MPU (IC16) and its peripheral circuits in the KRK-18H. IC16 mainly performs the followings;
(1) Serial communication with the Mobile transceiver.
(2) Controlling the microphone input path.
(3) Controlling the Control Head.
The KRK-18H has the serial communication circuit between the Mobile transceiver via the Control Head Remote unit (KRK-19B) and
the Control Head. This circuit consists of the CAN transceiver IC. This IC converts the UART signal to the CAN signal or the CAN
signal to the UART signal. To communicate between the KRK-18H and the KRK-19B, the CAN BUS is used.
2.2.4.1 MPU
The MPU is 32bit RISC processor, equipped with peripheral functions. The maximum operating clock of the MPU is 288MHz, and
power source are 3.3V/1.8V/1.2V DC. The MPU controls the Flash memory, the Mobile DDR, the Audio circuits, the Key detection IC
which is on the Control Head, the External I/O circuit, and the LCD Display.
2.2.4.2 Memory Circuit
Memory circuit consists of the MPU, the Flash memory (IC29), and the Mobile DDR (IC23).
The Flash memory is the nonvolatile memory and has capacity of 256Mbit that contains the program for the MPU and stores the data.
The program can be updated easily from PC through the Control Head. The Mobile DDR has capacity of 512Mbit. The MPU copies
the program from the Flash memory to the Mobile DDR and uses the Mobile DDR as a work area.
2.2.4.3 LCD control interface
The MPU controls the LCD which is in the Control Head through the Control Head interface connector (CN48). The LCD is controlled
by parallel bus with 8bit data width.
2.2.4.4 Key detection
The MPU can detect the keys on the Control Head. The keys are connected to the I/O expander IC in this unit which has the key matrix
function. When the key is pushed, I/O expander IC scans which key is pushed. The interrupt occurs for the MPU from the I/O expander
IC, and then the MPU reads the registers of the I/O expander IC and confirms which key is pushed.
2.2.4.5 External I/O
The KRK-18H has an external interface connector (CN2). The interface has two outputs and two inputs terminals. The output terminals
are the open drain type. The input terminals have the level shift circuit; these terminals can input the 5V signal.
CN1
Audio circuits
XC3-064
CAN transceiver
IC3
3.3V AVR
CAN transceiver
CN3
SB
54M
33A
32M

1-8 (No.RA062<Rev.001>)
2.3 COMPONENTS DESCRIPTION
2.3.1 Interface unit (XC3-063M-00) (KRK-18H)
2.3.2 Interface unit (XC3-064M-00) (KRK-19B)
2.4 TERMINAL FUNCTION
2.4.1 Interface unit (XC3-063M-00) (KRK-18H)
Ref. No. Part Name Use / Function
IC1 IC DC/DC step-down converter (53DC)
IC2 IC DC/DC step-down converter (39DC)
IC3 IC Voltage regulator (33A)
IC4 IC DC/DC step-down converter (18D)
IC5 IC Voltage regulator (33D)
IC6 IC Voltage regulator (50D)
IC7 IC DC switch (18D_Flash)
IC8 IC CAN transceiver
IC13 IC AF amplifier (MIC+/MIC-)
IC16 IC MPU
IC18 IC AF/DC amplifier (MIC/Vref)
IC20 IC Analog switch (MIC/ACC_MIC)
IC21, 22 IC Logic control
IC23 IC Mobile DDR SDRAM
IC29 IC NOR Flash memory
IC30 IC DC/DC step-down converter (12D)
Q1 FET DC switch (Open drain: AUXO1 output)
Q2 FET DC switch (Control for 18D)
Q3 FET DC switch (Open drain: AUXO2 output)
Q6 Transistor MIC AGC
Q7 FET DC switch (USB detection)
Q8 FET DC switch (AUXI1 input)
Q9 FET DC switch (AUXI2 input)
Q10 FET DC switch (Panel reset output)
D1 Diode Over current prevention
D4,5 Diode Over voltage protection
D6 Diode Catch diode (53DC)
D7 Diode Catch diode (39DC)
D8,9 Zener diode ESD protection
D10 Diode Over voltage protection
D11,12 Diode Rectifier Diode for MIC AGC
D13 Diode Over voltage protection
D15 Diode Reverse voltage protection
D16,17 Diode ESD protection
Ref. No. Part Name Use / Function
IC1 IC AF amplifier (MIC)
IC2 IC CAN transceiver
IC3 IC Voltage regulator (33A)
IC4 IC DC amplifier (Vref)
Pin No. Name I/O Function
CN1
1 /PRST I Reset signal
2 /PSW O Detection signal output of power switch
3 MIC+ O MIC signal hot
4 MIC- O MIC signal cold
5 GND - Ground
6 GND - Ground
7 GND - Ground
8 NC - No connection
9 SB I Switched +B power
10 IGN O Ignition sense
11 SP+ I Speaker signal
12 SPG - Speaker ground
13 GND - Ground
14 GND - Ground
15 CAN+ I/O High-level CAN bus line
16 CAN- I/O Low-level CAN bus line
CN2
1 GND - Ground
2 NC - No connection
3 NC - No connection
4 Ao2 O AUX output2
5 Ao1 O AUX output1
6 Ai2 I AUX input2
7 Ai1 I AUX input1
8 AUX_ME - AUX MIC ground
9 AUXMIC I AUX MIC signal
10 GND - Ground
11 SB O Switched +B power
12 IGN I Ignition sense
13 GND - Ground
CN48
1 SPG - Speaker ground
2 SPG - Speaker ground
3 SPG - Speaker ground
4 NC - No connection
5 SP+ O Speaker signal
6 SP+ O Speaker signal
7 SP+ O Speaker signal
8 NC - No connection
9 GND - Ground
10 GND - Ground
11 GND - Ground
12 GND - Ground

(No.RA062<Rev.001>)1-9
2.4.2 Interface unit (XC3-064M-00) (KRK-19B)
13 IGN - No connection
14 SB O Switched +B power
15 SB O Switched +B power
16 SB O Switched +B power
17 SB O Switched +B power
18 NC - No connection
19 54M O 5.3V output
20 NC - No connection
21 32M O 3.3V output
22 NC - No connection
23 18M O 1.8V output
24 NC - No connection
25 GND - Ground
26 USB_D+ I/O USB D+
27 GND - Ground
28 USB_D- I/O USB D-
29 GND - Ground
30 NC - No connection
31 Mic/VBUS I MIC signal/ USB VBUS detection
32 ME - MIC ground
33 /PTT I PTT input
34 DM/KVL I/O DTMF MIC detection/KVL detection
35 /PSW I Detection signal input of power switch
36 TXD O UART transmit data
37 RXD I UART receive data
38 GND - Ground
39 I2CDT I/O I2C serial data
40 I2CCK O I2C serial clock
41 /KEYINT I Key interrupt
42 P_TEMP - No connection
43 /CS O LCD driver chip-select signal
44 /LCDRST O LCD driver reset signal
45 /RD O LCD driver RD signal
46 D[7] I/O LCD driver data
47 D[6] I/O LCD driver data
48 D[5] I/O LCD driver data
49 D[4] I/O LCD driver data
50 D[3] I/O LCD driver data
51 D[2] I/O LCD driver data
52 D[1] I/O LCD driver data
53 D[0] I/O LCD driver data
54 /WR O LCD driver WR signal
55 A[23] O LCD driver data/command switch signal
56 GND - Ground
57 R_SET2 - No connection
58 R_SET1 - No connection
Pin No. Name I/O Function
59 R_SET0 - No connection
60 GND - Ground
Pin No. Name I/O Function
CN1
1 GND - Ground
2 R_SET0 - No connection
3 R_SET1 O Head type discern signal1
4 R_SET2 O Head type discern signal2
5 GND - Ground
6 A[23] - No connection
7 /WR - No connection
8 D[0] - No connection
9 D[1] - No connection
10 D[2] - No connection
11 D[3] - No connection
12 D[4] - No connection
13 D[5] - No connection
14 D[6] - No connection
15 D[7] - No connection
16 /RD - No connection
17 /PRST I Reset signal
18 /CS - No connection
19 P_TEMP - No connection
20 /KEYINT - No connection
21 I2CCK - No connection
22 I2CDT - No connection
23 GND - Ground
24 RXD O UART receive data
25 TXD I UART transmit data
26 /PSW O Detection signal output of power switch
27 DM/KVL - No connection
28 /PTT - No connection
29 ME - MIC ground
30 MIC O MIC signal
31 NC - No connection
32 GND - Ground
33 USB_D- - No connection
34 GND - Ground
35 USB_D+ - No connection
36 GND - Ground
37 NC - No connection
38 18M - No connection
39 NC - No connection
40 32M I 3.3V input
41 NC - No connection
Pin No. Name I/O Function

1-10 (No.RA062<Rev.001>)
42 54M I 5.3V input
43 NC - No connection
44 SB I Switched +B power
45 SB I Switched +B power
46 SB I Switched +B power
47 SB I Switched +B power
48 IGN O Ignition sense
49 GND - Ground
50 GND - Ground
51 GND - Ground
52 GND - Ground
53 NC - No connection
54 SP+ I Speaker signal
55 SP+ I Speaker signal
56 SP+ I Speaker signal
57 NC - No connection
58 SPG - Speaker ground
59 SPG - Speaker ground
60 SPG - Speaker ground
CN3
1 /PRST O Reset signal
2 /PSW I Detection signal input of power switch
3 MIC+ I MIC signal hot
4 MIC- I MIC signal cold
5 GND - Ground
6 GND - Ground
7 GND - Ground
8 SB O Switched +B power
9 NC - No connection
10 IGN - Ignition sense
11 SP+ O Speaker signal
12 SPG - Speaker ground
13 GND - Ground
14 GND - Ground
15 CAN+ I/O High-level CAN bus line
16 CAN- I/O Low-level CAN bus line
Pin No. Name I/O Function

(No.RA062<Rev.001>)1-11
SECTION 3
DISASSEMBLY
3.1 Precautions for Disassembly
3.1.1 How to remove the KRK-18H rear panel
Insert and remove the flat-head screwdriver as shown in the figure.
3.1.2 Remove the top cover from the shield cover (KRK-18H only)
(1) There are three shield covers on the interface unit, the top covers can be removed.
(2) Use tweezers to slightly lift the edge of the top cover. <1>
(3) As you do step 2 above, vary the position you hold the top
cover as you lift it, and remove the top cover <2>.
Note:
Once the top cover is removed, it cannot be used again.
Note:
Push evenly on the top cover and be careful that you do not
bend it as you install it on the shield cover.
Note:
How to stick the sheet on the shield cover.
Stick the sheet according to the line as shown in the figure.
Insert the screwdriver within this range.
Shield cover (with sheet)Shield cover (with sheet)
Shield coverShield cover
<1><1><1>
<2> <2> <2>

1-12 (No.RA062<Rev.001>)
3.1.3 Assembled Parts Information
When “Main Parts” is changed (ordered), “Assembled Parts” should also be changed (ordered) together.
The Shielding Cover is non-reusable parts. It requires the new one to get the radio’s performance after repairs.
KRK-18H
KRK-19B
SECTION 4
ADJUSTMENT
This service manual does not describe ADJUSTMENT.
(There is no adjustment item on KRK-18H and KRK-19B.)
Main Parts Assembled Parts
Part Name Part Number Part Name Part Number
REAR PANEL A2D-0026-00 STANDARD LABEL B4C-0632-00
INTERFACE UNIT XC3-063M-01 SHIELDING COVER F10-3225-05
SHIELDING COVER F1B-0027-00
SHEET G1B-0343-00
Main Parts Assembled Parts
Part Name Part Number Part Name Part Number
MAIN PANEL A6C-0089-00 STANDARD LABEL B4C-0632-00

(No.RA062<Rev.001>)1-13
SECTION 5
TROUBLESHOOTING
5.1 KRK-18H Fault Diagnosis of the BGA (Ball Grid Array) IC
Overview
A flowchart for determining whether or not the transceiver can be powered on (the LCD does not function even if the power switch is
turned on) due to broken BGA parts. Connect to the Control Head and RF Deck of the NX-3720/3820 using the KRK-18H, KCT-71
and KRK-19B.
Confirm whether there is a defect in the KRK-18H.
Note:
The firmware of the NX-3720/3820 RF Deck and KRK-18H must be the same version.
BGA parts
MPU (IC16), mobile DDR (IC23), Flash memory (IC29)
R46 1.2V
18D 1.8V
33D
1.8V
53DC L60 5.3V
Pass
Pass
Checking the SB (Battery) voltage
Standard voltage
K type 13.6V 15%
Points to be checked
SB TL3
E type 10.8V~15.6V
NOTE:
Depends on the battery performance, it may be
less than the voltage value that has been
described above.
Checking the power supply voltage
NOTE:
Fail
Points to be checked Standard voltage
Remove the top cover of the BLS to confirm.
And cut the cross bridge part.
12D
18D_Flash
R47
R45
R60
3.3V
Fail
Pass
Checking the Clock
Points to be checked Standard state
amplitude / frequency
R62 (MPU side) 1.2Vp-p / 19.2MHz
Checking MPU reset signal output from the MPU
Points to be checked Standard voltage
/PRST
D10 (Anode side) 1.8V
Pass
Fail
Fail
The BGA parts are not broken.
If the SB is unstable, check the connection and the SB
output from the Mobile Transceiver and the KRK-19B.
NOTE:
"12D" is not Standard voltage.
[MPU]
Remove L12~L16 to check the voltage of the 12D.
If the voltage becomes normal, the removed parts or the
subsequent parts are broken.
IC30 (12D DC/DC Converter Device) is fragile in the
scratch. Be careful when you touch this part.
"18D" is not Standard voltage.
[MPU]
Remove L17 and L18 to check the voltage of the 18D.
If the voltage becomes normal, the removed parts or the
subsequent parts are broken.
[mobile DDR]
Remove L30 to check the voltage of the 18D.
If the voltage becomes normal, the removed part or the
subsequent parts are broken.
[LCD]
Remove L61 to check the voltage of the 18D.
If the voltage becomes normal, the removed part or the
subsequent parts are broken. (Including FFC)
"33D" is not Standard voltage.
[MPU]
Remove L19 to check the voltage of the 33D.
If the voltage becomes normal, the removed part or the
subsequent parts are broken.
[Flash Memory]
Remove L36 to check the voltage of the 33D.
If the voltage becomes normal, the removed part or the
subsequent parts are broken.
[LCD]
Remove L59 to check the voltage of the 18D.
If the voltage becomes normal, the removed part or the
subsequent parts are broken. (Including FFC)
"18D_Flash" is not Standard voltage.
[Flash Memory]
Remove L35 to check the voltage of the 18D_Flash.
If the voltage becomes normal, the removed part or the
subsequent parts are broken.
Amplitude or Frequency is abnormal.
Remove R62 to check the amplitude and frequency of X1.
If the amplitude and frequency becomes normal, the MPU
or removed part are broken.
"/PRST" is not Standard voltage.
If voltage of TL9 is over 1.8V, check D10, R69 and C10.
If those parts are normal, the MPU is broken.
"53DC" is not Standard voltage.
[LCD]
Remove L60 to check the voltage of the 53DC.
If the voltage becomes normal, the removed part or the
subsequent parts are broken. (Including FFC)

1-14 (No.RA062<Rev.001>)
0V
LCDRST 0V
0V
1.8V
3.3V
Pass
Pass
Points to be checked
Checking the Flash Memory reset signal output from the MPU
Standard voltagePoints to be checked
/FRST
D13 (Anode side)
D13 (Cathode side)
Fail
Pass
Fail
Checking the Control signal
Pass
Fail
Fail
Pass
When Anode side of D13 is not Standard voltage,
check R167.
If R167 is normal then the Flash Memory is broken.
When Cathode side of D13 is not Standard voltage, the
MPU is broken.
Checking the clock output from the MPU
Checking the LCD displays reset signal
Checking the LCD displays control signal
When an error display appears on the LCD
The LCD displays “INIT ERROR 1”.
NOTE:
This is displayed after turning on the power.
Descriptions of signal names
1) /PRST
2) /FRST
3) /CS2_1
4) /LCDRST
5) /CS4_1
: MPU reset signal
: Flash Memory reset signal
: Flash Memory chip select signal
: LCD reset signal
: LCD controller chip select signal
"LOW" "Reset"
"LOW"
"LOW"
"LOW"
"LOW"
"Reset"
"Active"
"Reset"
"Active"
Points to be checked Standard voltage
After power-on, and
1.8V fixed later
1.8V,1.8V
TL31/CS2_1
Frequency
144MHz
144MHz
TL19
TL18
DDR_CLKP
NOTE:
If the confirmation result is normal, return the top
cover of the removed BLS.
Depending on the specifications of the oscilloscope,
normal waveforms cannot be seen. (Confirm that
the waveform is changing)
DDR_CLKN
Points to be checked Standard voltage
Q10 (Gate)
/LCDRST L50 (CN48 side) 3.3V
1.8V1.8V
/CS4_1 CP3(4pin)
Standard voltage
After power-on, and
It is unlikely that the BGA parts are broken.
Fail
Points to be checked
The operation of "/CS2_1" is not Standard voltage.
Remove R164.
If the voltage of the MPU side always 0V or the
Waveform does not change, the MPU is broken.
If the voltage of the MPU side becomes normal, the
Flash Memory or removed part is broken.
The clock output frequency of "DDR_CLKP" or
"DDR_CLKN" are abnormal.
If the "DDR_CLKP", "DDR_CLKN" frequency is not
144MHz, the MPU, the mobile DDR or the Flash memory
may be broken.
"LCDRST" is not Standard voltage.
Remove Q10.
If the "LCDRST" voltage (Q10 Gate pad) does not become
0V, the MPU, the mobile DDR or the Flash memory may
be broken.
"/CS4-1" is not Standard voltage.
Remove CP3.
If the "/CS4_1" voltage (CP3 4pin pad) does not become
normal, the MPU, the mobile DDR or the Flash memory
may be broken.
This is displayed when Write / Read from the MPU to the
mobile DDR is abnormal.
The mobile DDR may be broken.

(No.RA062<Rev.001>)1-15
5.2 Replacing Interface Unit
Interface Unit Information
* The KRK-19B doesn’t have a service interface unit. Please order normal interface unit (XC3-064M-00) listed in parts list.
Method of confirming "Original Interface Unit" and "Service Interface Unit"
Supplied Accessories of "Service Interface Unit"
"Service Interface Unit" Data
The following data is written on the service unit.
After Changing the PCB
After changing the printed circuit board, update Firmware following the instructions.
(1) Connection procedure
Connect the transceiver to the personal computer using the interface cable (KPG-46U/46X).
Note:
You can only program firmware from the 8-pin microphone connector on the SUB (Display) unit of the NX-3720/3820.
(2) Programming
a) Start up the KENWOOD Firmware loader (KFL).
b) Set the firmware to the KENWOOD Firmware loader (KFL).
c) Turn the transceiver power ON.
d) Check the connection between the transceiver and the personal computer.
e) Press write button in the window.
When the transceiver starts to receive data, the [LOADING] display on the LCD.
The Firmware is written to the RF Deck (NX-3720/3820) and the KRK-18H at the same time.
f) If writing ends successfully, the checksum is calculated and a result is displayed.
Model Name Orginal Interface
Unit Number
For Service Interface
Unit Number
KRK-18H XC3-063M-00 XC3-063M-01
TL47
TL41
TL40
TL39 TL38
TL22 TL21
TL14
TL13
TL12
TL11
TL10
TL9
TL4
TL3
R253
R252
R203
R201
R192
R190
R187
R171 R169
R163
R162
R161R160
R157
R156
R155
R154 R153
R147R146
R145
R144
R143
R140
R139
R138R137
R135
R134
R132
R131
R126
R125
R124
R123
R122
R115
R114
R108
R104
R103
R100
R99
R96
R95
R94
R93
R60
R54
R51
R48
R47
R46
R45
R38
R37
R36
R35
R30
R29
R27
R22
R8
Q10
Q7
Q6
Q2
L65
L63 L62
L61
L60
L59
L58
L57
L50
L44
L41 L40L39
L21 L20
L19
L18
L17
L16
L15
L14
L13
L12
L8
L7
L6
L5
L4
L2
IC30
IC22
IC21
IC20 IC18
IC13
IC7
IC5
IC4
IC3
IC2
E1
D12D11
D7
CP3 CP2 CP1
CN48
C312
C311
C250
C224
C223
C219
C218
C216
C208
C207
C205 C203
C202
C196
C192
C188
C175
C174
C172
C171
C164
C163
C159
C158
C150
C146
C144C143
C142
C141C140
C139
C138
C137
C133 C132
C131
C118
C116
C113
C112
C110
C109
C108
C107
C106
C105
C104
C103
C102
C101
C100
C99
C92
C91
C89
C88
C87
C86
C85
C83
C82
C80
C78
C77
C76
C75
C74
C73
C71
C69
C68
C67 C66
C65
C64
C63
C62
C61
C60 C59
C58
C57
C56
C51
C46
C44
C42
C41
C40
C39
C38
C37 C36
C32
C31
C27
C25
C23
C3
C2
C1
SRV
IC5 IC7
IC21
IC22
IC4 CN48
IC20 IC18
IC13
IC2
IC3
XC3-063
J7C-0267-00
KRK-18H
The 0 ohm resistor (R501) is mounted on the "SRV" silk print
part of the Service Interface unit (XC3-063M-01).
Item (Including Parts Number) Quantity
Interface Unit (XC3-063) 1
Data Type Description
Firmware NX-3720/3820 Firmware

1-16 (No.RA062<Rev.001>)
5.3 KRK-18H Operating Method of Enforced Firmware Overwriting Mode
Enforced firmware overwriting mode is a mode to forcibly overwrite the transceiver firmware when the transceiver key operation does
not allow the transceiver to enter the firmware programming mode, for instance, when the transceiver fails to start up due to the
transceiver failure.
(1) Prepare the followings:
• RF Deck of the Mobile transceiver (NX-3720 or NX-3820)
• Control Head of the Mobile transceiver (NX-3720 or NX-3820)
• Control Head interface kit (KRK-18H)
• Control Head remote kit (KRK-19B)
• Remote control cable (KCT-71)
• Regulated DC power supply
• Programming interface cable (KPG-46U or KPG-46X)
• Power cable
(2) Remove the operation panel from the Mobile transceiver. As illustrated, connect properly a RF Deck and Control Head of the
Mobile transceiver, KRK-18H, KRK-19B, KCT-71, regulated DC power supply, programming interface cable (KPG-46U or KPG-
46X) and power cable.
(3) While FLDM terminal has a short-circuit with GND terminal on the KRK-18H PCB, turn its power ON.
Left: FLDM terminal
Right: GND terminal

(No.RA062<Rev.001>)1-17
(4) Upon startup of FLDM loader, "FIRMWARE PROG" appears on an LCD screen.
(5) Start KFL up, select the desired firmware you wish to overwrite, select the COM port number and baud rate, and then click the
"Write" button.
Note:
Configuring "Auto" for baud rate automatically apply the maximal speed of baud rate allowed for a programming cable connected
to the selected COM port number.
Upon start of overwriting on the transceiver, "LOADING" appears on an LCD screen.
(6) Upon completion of the firmware overwriting, "CHECKSUM xxxx" appears on an LCD screen.

MEMO

(No.RA062<Rev.001>) 2-1 2-1 (No.RA062<Rev.001>)
PRECAUTIONS ON SCHEMATIC DIAGRAMS
* Due to the improvement in performance, some part numbers shown in the circuit diagrams
may not agree with those indicated in the Parts List.
* The parts numbers, values and rated voltage etc. in the Schematic Diagrams are for
reference only.
* Since the circuit diagrams are standard ones, the circuits and circuit constants may be
subject to change for improvement without any notice.
* The parts of the symbol with " * " may vary depending on model. Refer to the parts list for details.
* The parts of the symbol with " $ " are unmounted parts.

(No.RA062<Rev.001>) 2-2 2-2 (No.RA062<Rev.001>)
B
A
4321
B
A
4321
X1
TL50
TL49
TL46
TL45
TL36
TL34
TL33TL32
TL31
TL30
TL28
TL27 TL26
TL25
TL23
TL20
TL19
TL18
TL17
TL16
TL15
TL8
TL7
R198
R197
R194
R193
R174
R170 R167
R164
R136
R121 R120
R119
R113
R112
R111
R110 R109
R86 R85
R82
R81 R80
R79
R78 R77
R76
R69
R68
R67
R66
R65
R63
R62
R61
R59
R58
R57
R56
R55
R53
R52
R42
R41
R40R39
R34R33
R32
R31
R28
R13 R12
R10
R9
R7
R3
Q9
Q8
Q3
Q1
L67
L66
L64
L56
L55
L52 L51
L46
L45
L36
L35
L30
L22
L3
L1
IC29
IC23
IC16
IC8
IC6
IC1
E3
E2
D17D16
D15
D13
D10
D9
D8
D6
D5
D4
D1
CN2
CN1
C253
C220
C211
C210
C193
C191
C189
C187
C186
C185
C176C173
C169 C168 C162 C161 C157
C156
C155
C97
C95
C94
C93
C90
C81
C79
C72 C70
C49
C35
C34 C33
C30
C26
C24
C21 C20
C15
C11 C10
C7
C6
C5C4
IC23
IC16
IC29
IC8
IC6
CN1
CN2
IC1
TL47
TL41
TL40
TL39 TL38
TL22 TL21
TL14
TL13
TL12
TL11
TL10
TL9
TL4
TL3
R253
R252
R203
R201
R192
R190
R187
R171 R169
R163
R162
R161R160
R157
R156
R155
R154 R153
R147R146
R145
R144
R143
R140
R139
R138R137
R135
R134
R132
R131
R126
R125
R124
R123
R122
R115
R114
R108
R104
R103
R100
R99
R96
R95
R94
R93
R60
R54
R51
R48
R47
R46
R45
R38
R37
R36
R35
R30
R29
R27
R22
R8
Q10
Q7
Q6
Q2
L65
L63 L62
L61
L60
L59
L58
L57
L50
L44
L41 L40L39
L21 L20
L19
L18
L17
L16
L15
L14
L13
L12
L8
L7
L6
L5
L4
L2
IC30
IC22
IC21
IC20 IC18
IC13
IC7
IC5
IC4
IC3
IC2
E1
D12D11
D7
CP3 CP2 CP1
CN48
C312
C311
C250
C224
C223
C219
C218
C216
C208
C207
C205 C203
C202
C196
C192
C188
C175
C174
C172
C171
C164
C163
C159
C158
C150
C146
C144C143
C142
C141C140
C139
C138
C137
C133 C132
C131
C118
C116
C113
C112
C110
C109
C108
C107
C106
C105
C104
C103
C102
C101
C100
C99
C92
C91
C89
C88
C87
C86
C85
C83
C82
C80
C78
C77
C76
C75
C74
C73
C71
C69
C68
C67 C66
C65
C64
C63
C62
C61
C60 C59
C58
C57
C56
C51
C46
C44
C42
C41
C40
C39
C38
C37 C36
C32
C31
C27
C25
C23
C3
C2
C1
SRV
IC5 IC7
IC21
IC22
IC4 CN48
IC20 IC18
IC13
IC2
IC3
XC3-063
J7C-0267-00
KRK-18H
--- Component side view/Side A (J7C-0267-00) ---
INTERFACE UNIT (XC3-063M-00 (KRK-18H_M)
PRINTED CIRCUIT BOARD
--- Foil side view/Side B (J7C-0267-00) ---