LG RAT376B Schematic

MODEL: RAT376B (RAS376BF/W)SERVICE MANUAL

Internal Use Only

Website http://biz.lgservice.com

Mini Hi-Fi System

SERVICE MANUAL

P/NO : AFN74972241 JANUARY, 2011

MODEL:

RAT376B

(RAS376BF/W)

CAUTION

BEFORE SERVICING THE UNIT, READ THE “SAFETY PRECAUTIONS”
IN THIS MANUAL.

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

SERVICE INFORMATION FOR EEPROM .......................................................................................... 1-6

PROGRAM DOWNLOAD GUIDE ........................................................................................................... 1-7

SPECIFICATIONS ....................................................................................................................................... 1-9

1-2

SERVICING PRECAUTIONS

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.

Storage in conductive bag

Drop 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.

NEVER look directly at the laser beam, and don’t allow
contact with fingers or other exposed skin.

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.

Pressure

Magnet

How to hold the pick-up

Cotton swab

Conductive Sheet

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.

1-3

Pressure

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 magnet­ism 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 stat­ic 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.

Armband

Resistor
(1 MΩ)

Resistor
(1 MΩ)

Conductive
Sheet

1-4

ESD PRECAUTIONS

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

SERVICE INFORMATION FOR EEPROM

POWER ON

FLD no disc status or AUX status.

Remote control ‘2’ + 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 STOP key

FLD ‘write ok’

DETECT NEW EEPROM
(OPTION EDIT SCREEN)

NAME

OPT0
OPT1
OPT2
OPT3
OPT4
OPT5
OPT6
OPT7
OPT8
OPT9

HEX

05
00
00
00
00
08
80
06
50
08

Remote control ‘Fwd skip’ +

Front ‘STOP’ push same timing

FLD ‘E2P CLR’

Completed

1-6

PROGRAM DOWNLOAD GUIDE

1. AUDIO PROGRAM

Download program file name must be RAT376.HEX

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

READ

↓

FIRMWARE

↓

WRITE 00 .. 100

↓

UPDATED

↓

POWER OFF AUTOMATICALLY ← When completed, remove USB device.

1-7

2. CD PROGRAM

Download program file name must be HB001_DATE_00.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

READ

↓

FIRMWARE

↓

WRITE 00 .. 100

↓

FINISH

↓

POWER OFF AUTOMATICALLY ← When completed, remove USB device.

1-8

SPECIFICATIONS

• GENERAL

Power supply Refer to main label.
Power consumption Refer to main label.
Net Weight 3.4 kg
External dimensions (W x H x D) 202 x 307 x 297.5 mm (without foot)
BUS power supply (USB) DC 5 V 500 mA
Operating conditions Temperature 5 °C ~ 35 °C (41 °F to 95 °F)
Operation status: Horizontal
Operating humidity 5 % ~ 90 %
Laser Semiconductor laser, wavelength 650 nm

• INPUTS/OUTPUTS

Analog Audio In 2.0 Vrms (1 kHz, 0 dB), 600 Ω, RCA jack (L,R)x 1

• TUNER FM / AM[MW]

FM Tuning Range 87.5 to 108.0 MHz or 87.50 to 108.00 MHz
FM Intermediate Frequency 128 kHz
AM Tuning Range 522 to 1 620 kHz, 520 to 1 710 kHz or 522 to 1 710 kHz
AM Intermediate Frequency 45 kHz

• AMPLIFIER

Stereo mode 110 W + 110 W (4 Ω at 1 kHz, THD 10 %)
Surround mode
Front 110 W + 110 W (4 Ω at 1 kHz, THD 10 %)
Subwoofer 150 W (3 Ω at 60 Hz, THD 10 %)

• CD

Frequency response 40 Hz - 20 kHz
Signal-to-noise ratio 75 dB
Dynamic range 80 dB

• SPEAKERS

Front speaker (RAS376BF) Passive subwoofer (RAS376BW)
Type 2 Way 2 Speaker 1 Way 1 Speaker
Impedance 4 Ω 3 Ω
Rated Input Power 110 W 150 W
Max. Input Power 220 W 300 W
Net Dimensions (W x H x D) 232 x 360 x 265 mm 250 x 345 x 330 mm
Net Weight (1EA) 3.15 kg 5.35 kg

1-9

MEMO

1-10

SECTION 2

CABINET & MAIN CHASSIS

CONTENTS

EXPLODED VIEWS ..................................................................................................................................... 2-3

1. CABINET AND MAIN FRAME SECTION (RAT376) ................................................................................ 2-3

2. MECHANISM DECK SECTION (CDM-345) ............................................................................................. 2-5

3. PACKING ACCESSORY SECTION ......................................................................................................... 2-7

4. SPEAKER SECTION ................................................................................................................................ 2-8

2-1

MEMO

2-2

EXPLODED VIEWS

1. CABINET AND MAIN FRAME SECTION (RAT376)

460

260L

A42

A43

460

E

USB

FRONT

261

460

A26

CABLE2

460

460

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.

262

279

460

264

451

F

460

A47

SMPS

A

D

B

276

I

460

C

460

251

460

H

259

460

I

D

G

265

A44

A

B

MAIN

460

260R

A46

H

E

F

G

460

C

273 274

300

2-3 2-4

2. MECHANISM DECK SECTION (CDM-345)

MEMO

A26

01

1

2

0

01

A

1

0

A

0

02

A

01 2

2

43

6

03

6

01

2

8

01

9

43

4

01

3

01

7

5

01

43 1

00

2

00

3

00

10

0

02

A

01 2

9

01

6

3

0

A

01

2

03

2

43

7

6-25-2

3. PACKING ACCESSORY SECTION

824 AM Loop Antenna

801 Instruction Ass'y

808 Battery

804 Bag

825 FM Wire Antenna

900 Remote Control

803 Packing

2-7

802 Box

4. SPEAKER SECTION

4-1. FRONT SPEAKER (RAS376BF)

A60

2-8

4-2. PASSIVE SUBWOOFER (RAS376BW)

A90

2-9

MEMO

2-10

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 .................................................................. 3-16

1. POWER (SMPS) ................................................................................................................................... 3-16

2. μ-COM PART CHECK .......................................................................................................................... 3-20

3. IC101(S24CS16A01) 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. USB FUNCTION ................................................................................................................................... 3-28

WAVEFORMS ............................................................................................................................................. 3-29

WIRING DIAGRAM ................................................................................................................................... 3-33

BLOCK DIAGRAMS ................................................................................................................................. 3-35

1. OVERALL BLOCK DIAGRAM .............................................................................................................. 3-35

2. SMPS BLOCK DIAGRAM..................................................................................................................... 3-37

CIRCUIT DIAGRAMS ............................................................................................................................... 3-39

1. SMPS CIRCUIT DIAGRAM .................................................................................................................. 3-39

2. MICOM & AD CIRCUIT DIAGRAM ...................................................................................................... 3-41

3. PWM & AMP CIRCUIT DIAGRAM ....................................................................................................... 3-43

4. CD DSP & SERVO CIRCUIT DIAGRAM ............................................................................................. 3-45

5. FRONT CIRCUIT DIAGRAM ................................................................................................................ 3-47

6. USB CIRCUIT DIAGRAM ..................................................................................................................... 3-49

CIRCUIT VOLTAGE CHART ................................................................................................................. 3-51

PRINTED CIRCUIT BOARD DIAGRAMS ......................................................................................... 3-55

1. MAIN P.C.BOARD ................................................................................................................................ 3-55

2. SMPS P.C.BOARD ............................................................................................................................... 3-59

3. FRONT P.C.BOARD ............................................................................................................................. 3-60

4. USB P.C.BOARD .................................................................................................................................. 3-61

3-1

ONE POINT REPAIR GUIDE

1. NO POWER

If the unit doesn’t work by no power problem, repair the set according to the following
guide.

1-1. FUSE & BRIDGE DIODE

1-1-1. Solution

Please check and replace F901, BD901, TH901 on SMPS board.

1-1-2. How to troubleshoot (Countermeasure)

1) Check if the fuse F901 is open or short-circuit.

2) Check if the bridge diode DB901 is short-circuit by over current with a digital multi meter.

3) Check if the NTC thermistor TH901 is normal or open.

1-1-3. Service hint (Any picture / Remark)

< F901 >

If F901 is not short-circuit,

replace it with a same

specifi cations one.

replace it with a new one.

< BD901 >

If BD901 is short-circuit,

< TH901 >

If TH901 is open,

replace it with a new one.

3-2