LG CM4740 User manual

Mini Hi-Fi System
SERVICE MANUAL
MODEL: CM4740
(CM4740, CMS4740F/W)
CAUTION
BEFORE SERVICING THE UNIT, READ THE “SAFETY PRECAUTIONS”
IN THIS MANUAL.
MODEL: CM4740 (CM4740, CMS4740F/W)SERVICE MANUAL
4102,MARCH76592141NFA:ON/P
Website http://biz.lgservice.com
Internal Use Only

CONTENTS
SECTION 1 ........ GENERAL
SECTION 2 ........ CABINET & MAIN CHASSIS
SECTION 3 ........ ELECTRICAL
SECTION 4 ........ REPLACEMENT PARTS LIST
1-1

SECTION 1
SUMMARY
CONTENTS
SERVICING PRECAUTIONS................................................................................................................... 1-3
ESD PRECAUTIONS.................................................................................................................................. 1-5
HIDDEN KEY MODE................................................................................................................................... 1-6
SERVICE INFORMATION FOR EEPROM .......................................................................................... 1-7
PROGRAM DOWNLOAD & UPDATE GUIDE ................................................................................... 1-8
1. MCS PROGRAM....................................................................................................................................... 1-8
2. EQ PROGRAM ......................................................................................................................................... 1-9
SPECIFICATIONS ..................................................................................................................................... 1-10
1-2

NOTES REGARDING HANDLING OF THE PICK-UP
1. Notes for transport and storage
1) The pick-up should always be left in its conductive bag until immediately prior to use.
2) The pick-up should never be subjected to external pressure or impact.
2. Repair notes
1) The pick-up incorporates a strong magnet, and so should never be brought close to magnetic materials.
2) The pick-up should always be handled correctly and carefully, taking care to avoid external pressure and
impact. If it is subjected to strong pressure or impact, the result may be an operational malfunction and/or
damage to the printed-circuit board.
3) Each and every pick-up is already individually adjusted to a high degree of precision, and for that reason
the adjustment point and installation screws should absolutely never be touched.
4) Laser beams may damage the eyes!
Absolutely never permit laser beams to enter the eyes!
Also NEVER switch ON the power to the laser output part (lens, etc.) of the pick-up if it is damaged.
5) Cleaning the lens surface
If there is dust on the lens surface, the dust should be cleaned away by using an air bush (such as used
for camera lens). The lens is held by a delicate spring. When cleaning the lens surface, therefore, a cotton
swab should be used, taking care not to distort lens.
6) Never attempt to disassemble the pick-up.
Spring has excess pressure. If the lens is extremely dirty, apply isopropyl alcohol to the cotton swab.
(Do not use any other liquid cleaners, because they will damage the lens.) Take care not to use too much
of this alcohol on the swab, and do not allow the alcohol to get inside the pick-up.
Storage in conductive bag Drop impact
NEVER look directly at the laser beam, and don’t allow
contact with fingers or other exposed skin.
Magnet
How to hold the pick-up
Conductive Sheet
Cotton swab
Pressure
Pressure
1-3
SERVICING PRECAUTIONS

NOTES REGARDING COMPACT DISC PLAYER REPAIRS
1. Preparations
1) Compact disc players incorporate a great many ICs as well as the pick-up (laser diode). These components
are sensitive to, and easily affected by, static electricity. If such static electricity is high voltage, components
can be damaged, and for that reason components should be handled with care.
2) The pick-up is composed of many optical components and other high-precision components. Care must be
taken, therefore, to avoid repair or storage where the temperature or humidity is high, where strong magnet-
ism is present, or where there is excessive dust.
2. Notes for repair
1) Before replacing a component part, first disconnect the power supply lead wire from the unit
2) All equipment, measuring instruments and tools must be grounded.
3) The workbench should be covered with a conductive sheet and grounded.
When removing the laser pick-up from its conductive bag, do not place the pick-up on the bag. (This is
because there is the possibility of damage by static electricity.)
4) To prevent AC leakage, the metal part of the soldering iron should be grounded.
5) Workers should be grounded by an armband (1 MΩ)
6) Care should be taken not to permit the laser pick-up to come in contact with clothing, in order to prevent stat-
ic electricity changes in the clothing to escape from the armband.
7) The laser beam from the pick-up should NEVER be directly facing the eyes or bare skin.
Resistor
(1 MΩ)Conductive
Sheet
Resistor
(1 MΩ)
Armband
1-4

Electrostatically Sensitive Devices (ESD)
Some semiconductor (solid state) devices can be damaged easily by static electricity. Such components
commonly are called Electrostatically Sensitive Devices (ESD). Examples of typical ESD devices are integrated
circuits and some field-effect transistors and semiconductor chip components. The following techniques should
be used to help reduce the incidence of component damage caused by static electricity.
1. Immediately before handling any semiconductor component or semiconductor-equipped assembly, drain off
any electrostatic charge on your body by touching a known earth ground. Alternatively, obtain and wear a
commercially available discharging wrist strap device, which should be removed for potential shock reasons
prior to applying power to the unit under test.
2. After removing an electrical assembly equipped with ESD devices, place the assembly on a conductive surface
such as aluminum foil, to prevent electrostatic charge buildup or exposure of the assembly.
3. Use only a grounded-tip soldering iron to solder or unsolder ESD devices.
4. Use only an anti-static solder removal device. Some solder removal devices not classified as "anti-static" can
generate electrical charges sufficient to damage ESD devices.
5. Do not use freon-propelled chemicals. These can generate electrical charges sufficient to damage ESD
devices.
6. Do not remove a replacement ESD device from its protective package until immediately before you are
ready to install it. (Most replacement ESD devices are packaged with leads electrically shorted together by
conductive foam, aluminum foil or comparable conductive materials).
7. Immediately before removing the protective material from the leads of a replacement ESD device, touch the
protective material to the chassis or circuit assembly into which the device will by installed.
CAUTION : BE SURE NO POWER IS APPLIED TO THE CHASSIS OR CIRCUIT, AND OBSERVE ALL OTHER
SAFETY PRECAUTIONS.
8. Minimize bodily motions when handing unpackaged replacement ESD devices. (Otherwise harmless motion
such as the brushing together of your clothes fabric or the lifting of your foot from a carpeted floor can generate
static electricity sufficient to damage an ESD device).
CAUTION. GRAPHIC SYMBOLS
THE LIGHTNING FLASH WITH APROWHEAD SYMBOL. WITHIN AN EQUILATERAL TRIANGLE, IS
INTENDED TO ALERT THE SERVICE PERSONNEL TO THE PRESENCE OF UNINSULATED
“DANGEROUS VOLTAGE” THAT MAY BE OF SUFFICIENT MAGNITUDE TO CONSTITUTE A RISK OF
ELECTRIC SHOCK.
THE EXCLAMATION POINT WITHIN AN EQUILATERAL TRIANGLE IS INTENDED TO ALERT THE
SERVICE PERSONNEL TO THE PRESENCE OF IMPORTANT SAFETY INFORMATION IN SERVICE
LITERATURE.
1-5
ESD PRECAUTIONS

1-6
Push both Front key and RCU key to activate it for 5 seconds.
1. Disc Lock On/Off (CD Function Only Active)
Front Key : STOP
RCU Key : STOP
2. Check Version and Option code
Front Key : STOP
RCU Key : PLAY/PAUSE
You can change [Audio MCU Version <-> CD Controller Version <-> EEPROM Option] by SKIP+/-.
3. Clear EEPROM
Front Key : STOP
RCU Key : SKIP-
4. Edit EEPROM
Front Key : STOP
RCU Key : SKIP+
You can change the digit of option by SKIP+/-.
You can edit 0~f by REPEAT or PLAY/PAUSE key.
5. Bluetooth DUT
Front Key : STOP
RCU Key : PROGRAM
Bluetooth model only
6. Power Disc Lock On/Off (CD Function Only Active)
Front Key : STOP
RCU Key : EQ
7. Amp Clip On/Off
Front Key : STOP
RCU Key : Mute
Amp Clip Mode Change (Amp Clip On --> Amp Clip Off --> Level Down display).
HIDDEN KEY MODE

POWER ON
FLD no disc status or AUX status.
Remote control ‘Fwd skip’ + Front ‘STOP’
push same timing during 5 seconds.
FLD ‘OP-0….
Move to appropriate position and
make changes with remote control
‘skip, mode, play’ key.
Press ENTER key
FLD ‘write ok’
Remote control ‘Fwd skip’ +
Front ‘STOP’ push same timing
FLD ‘E2P CLR’
Completed
NAME
OPT0
OPT1
OPT2
OPT3
OPT4
OPT5
OPT6
OPT7
OPT8
OPT9
DETECT NEW EEPROM
(OPTION EDIT SCREEN)
HEX
05
00
00
02
00
01
81
06
40
00
1-7
SERVICE INFORMATION FOR EEPROM

1. MCS PROGRAM
Download program file name must be
- HG440_CM4740_DATE.bin : CM4740 4M Flash
- HG420_CM4740_DATE.bin : CM4740 2M Flash
- HG440_CM464P_DATE.bin : CM4640P (With Ipod)
If security program (Water Wall) is activated on your PC, you must save the file to the USB storage
device and disable the security software, then download the file to your set.
Caution: When downloading the file, you should neither unplug the USB device, change to the other
function, nor power off the device. USB device must be unplugged when the downloading
process is completed.
ON VFD DISPLAY SCREEN
NO USB
↓← Insert USB device at USB function.
SEARCH
↓
FIRMWARE
↓
FINISH
↓
POWER OFF MANUALLY ← When completed, remove USB device.
1-8
PROGRAM DOWNLOAD & UPDATE GUIDE

2. EQ PROGRAM
Download program file name must be EQ_PRG_CM4740_***.BIN
If security program (Water Wall) is activated on your PC, you must save the file to the USB storage
device and disable the security software, then download the file to your set.
Caution: When downloading the file, you should neither unplug the USB device, change to the other
function, nor power off the device. USB device must be unplugged when the downloading
process is completed.
ON VFD DISPLAY SCREEN
NO USB
↓← Insert USB device at USB function.
SEARCH
↓
EQ UP
↓
FINISH
↓
POWER OFF AUTOMATICALLY ← When completed, remove USB device.
1-9

SPECIFICATIONS
1-10
• GENERAL
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Dimensions (W x H x D) 206 x 308 x 284 mm
Net Weight (Approx.) 3.1 kg
Operating temperature 5 °C to 35 °C (41 °F to 95 °F)
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Bus Power Supply (USB) 5 V 500 mA
• INPUTS
57,)Bd0,zHk1(smrV0.2NIXUA Ω, RCA jack (L, R) x 1
)kcajoeretsmm5.3(smrV2.1NITROP
• TUNER
zHM00.801ot05.78rozHM0.801ot5.78egnaRgninuTMF
zHk0171ot225rozHk0171ot025,zHk0261ot225e (Optional)gnaRgninuTMA
• AMPLIFIER
3(W072+W072edomoeretS Ωat 1 kHz, THD 20 %)
Surround mode
3(W072+W072tnorF Ωat 1 kHz, THD 20 %)
3(W062refoowbuS Ωat 60 Hz, THD 20 %)
• CD
Frequency Response 100 to 20 000 Hz
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• FRONT SPEAKER
F0474SMCledoM
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3ecnadepmI Ω
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Net Dimensions (W x H x D) 300 x 358 x 265 mm
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• SUBWOOFER SPEAKER
W0474SMCledoM
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3ecnadepmI Ω
W062rewoPtupnIdetaR
W025rewoptupnI.xaM
Net Dimensions (W x H x D) 310 x 358 x 305 mm
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Design and specifications are subject to change without notice.

SECTION 2
CABINET & MAIN CHASSIS
CONTENTS
EXPLODED VIEWS..................................................................................................................................... 2-3
1. CABINET AND MAIN FRAME SECTION (CM4740) ................................................................................ 2-3
2. MECHANISM DECK SECTION (DP17TM3) ............................................................................................ 2-5
3. PACKING ACCESSORY SECTION ......................................................................................................... 2-7
4. SPEAKER SECTION ................................................................................................................................ 2-8
2-1

2-2
MEMO

EXPLODED VIEWS
1. CABINET AND MAIN FRAME SECTION (CM4740)
FRONT
463
463
F300
SMPS
MAIN
E
B
A
D
D
C
C
B
F
A
E
H
H
260L
260R
464
464
A47
264
269
262
460
464
464
263
255
255
464
464
A43
464
464
A46
464
265
266
A44
266
464
261
252
259
464
464
A42
251
253
CABLE1
NOTES) THE EXCLAMATION POINT WITHIN AN
EQUILATERAL TRIANGLE IS INTENDED
TO ALERT THE SERVICE PERSONNEL
TO THE PRESENCE OF IMPORTANT
SAFETY INFORMATION IN SERVICE
LITERATURE.

2. MECHANISM DECK SECTION (DP17TM3)
1026
1439
A001
1002
1005 1001
1049
1437
1437
1024
1024
1030
1024
1043
1045
A005
A006
1016
1013 1015
1020
1024
1003
1439
1018
1019
1011
1012
1437
1004

900 Remote Control
808 Battery
825 FM Wire Antenna
802 Box
801 Instruction Ass'y
804 Bag
803 Packing
803 Packing
3. PACKING ACCESSORY SECTION

A60
4. SPEAKER SECTION
4-1. FRONT SPEAKER (CMS4740F)

A90
4-2. SUBWOOFER SPEAKER (CMS4740W)

2-10
MEMO

SECTION 3
ELECTRICAL
CONTENTS
ONE POINT REPAIR GUIDE................................................................................................................... 3-2
1. NO POWER............................................................................................................................................ 3-2
2. NO BOOTING WHEN POWER ON THE SET ....................................................................................... 3-4
3. VFD IS NOT DISPLAYED WHEN POWER ON THE SET..................................................................... 3-5
4. NO OPERATION OF MD ....................................................................................................................... 3-6
5. NO SOUND .......................................................................................................................................... 3-11
AUDIO ELECTRICAL TROUBLESHOOTING GUIDE .................................................................. 3-17
1. POWER (SMPS)................................................................................................................................... 3-17
2. MCS PART CHECK.............................................................................................................................. 3-20
3. IC504(M24C16) CHECK....................................................................................................................... 3-20
4. FLD DISPLAY CHECK ......................................................................................................................... 3-21
5. PWM MODULATION CHECK .............................................................................................................. 3-22
6. POWER AMP PART CHECK ............................................................................................................... 3-24
7. TUNER / AUX FUNCTION CHECK...................................................................................................... 3-25
8. TUNER FUNCTION CHECK ................................................................................................................ 3-26
CDP ELECTRICAL TROUBLESHOOTING GUIDE ....................................................................... 3-27
1. CD FUNCTION ..................................................................................................................................... 3-27
2. DOUBLE USB FUNCTION................................................................................................................... 3-28
WAVEFORMS OF MAJOR CHECK POINT ..................................................................................... 3-29
1. SDRAM................................................................................................................................................. 3-29
2. SERVO ................................................................................................................................................. 3-29
3. AUDIO PATH........................................................................................................................................ 3-30
4. USB....................................................................................................................................................... 3-31
WIRING DIAGRAM ................................................................................................................................... 3-33
BLOCK DIAGRAMS................................................................................................................................. 3-35
1. SYSTEM BLOCK DIAGRAM................................................................................................................ 3-35
2. SMPS BLOCK DIAGRAM..................................................................................................................... 3-37
3. AUDIO PATH BLOCK DIAGRAM......................................................................................................... 3-39
4. POWER DIAGRAM .............................................................................................................................. 3-41
CIRCUIT DIAGRAMS...............................................................................................................................3-43
1. SMPS CIRCUIT DIAGRAM .................................................................................................................. 3-43
2. MAIN - DSP CIRCUIT DIAGRAM......................................................................................................... 3-45
3. MAIN - SERVO CIRCUIT DIAGRAM ................................................................................................... 3-47
4. MAIN - ADC/ PWM CIRCUIT DIAGRAM ............................................................................................. 3-49
5. MAIN - AMP CIRCUIT DIAGRAM ........................................................................................................ 3-51
6. FRONT CIRCUIT DIAGRAM................................................................................................................ 3-53
CIRCUIT VOLTAGE CHART................................................................................................................. 3-55
1. ICs......................................................................................................................................................... 3-55
2. CAPACITORS....................................................................................................................................... 3-57
PRINTED CIRCUIT BOARD DIAGRAMS ......................................................................................... 3-59
1. SMPS P.C.BOARD............................................................................................................................... 3-59
2. MAIN P.C.BOARD ................................................................................................................................ 3-61
3. FRONT P.C.BOARD............................................................................................................................. 3-63
3-1