LG SB74 User manual

MODEL : SB74
SERVICE MANUAL
Stylish Powerful Portable Boom Box
SERVICE MANUAL
CAUTION
BEFORE SERVICING THE UNIT, READ THE “SAFETY PRECAUTIONS”
IN THIS MANUAL.
MODEL : SB74
Website http://biz.lgservice.com
Internal Use Only
SEPTEMBER, 2009P/NO : AFN73250927

1-1
SECTION 1. GENERAL
• SERVICING PRECAUTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
• ESD PRECAUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
•
PROGRAM DOWNLOAD GUIDE
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
• SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
SECTION 2. EXPLODED VIEWS
• CABINET AND MAIN FRAME SECTION (SB74) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
• PACKING ACCESSORY SECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
SECTION 3. ELECTRICAL PART
• TROUBLESHOOTING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
• WAVEFORMS OF MAJOR CHECK POINT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
• WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
• BLOCK DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15
• CIRCUIT DIAGRAMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
• CIRCUIT VOLTAGE CHART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27
• PRINTED CIRCUIT DIARGAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-29
SECTION 4. REPLACEMENT PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
[CONTENTS]

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.
2. Repair notes
1) The pick-up incorporates a strong magnet, and so should never be brought close to magnetic mate-
rials.
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 malfunc-
tion 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, there-
fore, a cotton swab should be used, taking care not to distort this.
6) Never attempt to disassemble the pick-up.
Spring by 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 fingers or other exposed skin.
Magnet
How to hold the pick-up
Conductive Sheet
Cotton swab
Pressure
Pressure
SECTION 1. GENERAL

1-3
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 compo-
nents 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 of 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 pre-
vent 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.
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.
SAFETY PRECAUTIONS

1-5
PROGRAM UPGRADE PROCESS
Important Notice : When ugrade the software running,
Do not shut down the power, it may damage the unit
1. Copy the software file into the USB flash, As the file name is [SB74_VXX.mcs]
2. Insert the USB flash into the USB host
3. Set Function to the USB position.
Appear onto the LCD
CHECKING
UPGRADE
SUCCESS
4. After finish, Un-plug the AC inlet about 2sec. Than connect the AC inlet source again.
5. Software upgrade completed.
6. You can check the software version.
7. At Power on mode, Press STOP button of the set and PLAY key of the RCU together
LCD shows SB74_VXX(version)

1-6
GENERAL
Power supply Refer to main label.
Power consumption Refer to main label.
Net Weight 3.3 kg
External dimensions (W x H x D) 524 x 155 x 288 mm
CD
Laser Semiconductor laser, wave length 780nm
Frequency response (Audio) 100Hz to 18KHz
Single to noise ratio More than 55dB
Dynamic range (Audio) More than 50dB
TUNER(FM)
Tuning range 87.5 ~ 108MHz
Intermediate Frequency 128KHz
Oscillator frequency 32.768KHz
Frequency response (Audio) 100 Hz ~ 10 KHz
AMPLIFIER
PORTABLE IN
Out put Power 7.5 W + 7.5 W
In put sense 500 mV
Frequency response (Audio) 100 Hz ~ 18 KHz
Signal to Noise Ratio More than 55dB
SPEAKER
Model G-C40-55-8F-10W
Type 1 Way 1 Speaker
Impedance 8 Ω
Rfrequency Response 120 Hz ~ 20 KHz
Rated Input Power 8 W
Max. Input Power 10 W
Net Dimension (HxDxd) 42 x 102 x50 mm
Net Weight 240 g
Designs and specifications are subject to change without pior notice.
SPECIFICATIONS

B
C
A
M
F
K
NN
L
E
D
I
L
I
H
M
G
K
C
J
E
J
D
G
H
F
A
B
MCU SMPS
MAIN
251
252
252
254
258
255
263
264
265
263
A47
270
271
272
278
455
273
269 457
268
266
A42
A43
262
261
260
A46
A45
267
256 453
252A
257L 257R
259L
259R
CABLE1
CABLE4
279R
279L
A26
280
300
277A
277B
276
275R
275L
274L
274R
CABLE3
CABLE2
BELT1
277C
458
461
463
456
462
456
462
451
460
460
451
458
458
451
451
451
460
FRONT
USB
• CABINET AND MAIN FRAME SECTION (SB74)
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.
SECTION 2. EXPLODED VIEWS
2-1 2-2

2-3 2-4

2-5
• PACKING ACCESSORY SECTION
Remote Control900
Battery
808
Instruction Ass'y801
Packing803
Box
802
Packing
803
Bag804

2-6

3-1
TROUBLESHOOTING GUIDE
1. SMPS PART
YES
YES
YES
NO Replace the F901 (Use same type Fuse)
NO Replace the BD901
NO Replace the R901
Is the F901 nomal?
Is the BD901 nomal?
Is the R901 nomal?
YES
Power Line of Main PCB is short
12V
NO Is the D911 nomal?Is Vcc(9V~25V) supplied to IC911 pin5?
YES
Check or replace the D911
NO Replace the D952Is the D952 nomal?
YES
NO Replace the D950Is the D950 nomal?
YES
NO
2. P-SENS PART
Check U301A
Does +4V appear
at U301A
YES
Is the D702 nomal?
Check JK600 pin21
YES
Replace the D702
Check IC603 pin58
SECTION 3. ELECTRICAL PART
Check D306 Refer SMPS 12V
Check
NO NO NO
NO NO

3-2
3. MUTING CIRCUIT (MUTE)
NONONO
Does “High” appear
at Q206, Q208 “B”?
YES
Check D205,D204
MUTE
Check R202,R203 Check JK601 pin50
NO
Check the “Low” of
Q206, Q208 “C”
YES
NO Replace Q206, Q208 Check R635
4. AUDIO ABNORMAL
NO
YES
YES
Check the connection of speakers
NO Check the “High” of U200 pin7
NO Check the function input
Check the output of U200 pin1,2,14,15
Check the input signal of U200 pin4,12
Check the DC 12V of U200 pin3,13
YES
NO NormalCheck the FB302
Check the Power Circuit
YES
NO
Check the IC603 pin81
“HIGH” or “LOW”
YES
Replace IC603

3-3
5. AUDIO ABNORMAL (FUNCTION MODE)
YES
YES
NO Check the output signal of U703 pin55, 57
and refer to CD troubleshooting
Check the input signal of U503 pin3, 4
CD / USB
Check the output signal of U503 pin19, 23
YES
PORTABLE
Check the input
signal of U503 pin7,8
NO Check the input
signal CN500
NO Check L800, L802 NO Check R800, R801
YES
Check the output signal
of U503 pin19,23
NO
Check C810, C811
YES
TUNER
Check the input
signal of U503 pin1,2
NO
Check the output signal
of U101 pin5,6
NO
Check the output signal
of C102,C103
NO
Check the output signal
of R100,R101
YES
Check the output signal
of U503 pin19,23

3-4
7. IC603 ABNORMAL
YES
YES
Check both end voltage of IC302 3.3V/6.2V
NO Check or replace R601
NO Check or replace X600
Check both end voltage of IC605(1.2V / 3.3V)
Check IC603 pin13, 47, 94, 120,
122, 124 (1.2V)
Check IC603 pin111, 112 X600 operation
YES
NO Check IC602 Reset circuit
When power supply to IC603 pin107
(Low →High)
OK
YES
NO
NO
NONO
U302 3.3V output
normal ?
YES
OK
Replace ZD302
Check Q308 output
normal?
YES
Check
ZD302 normal?
YES
Check R308
YES
NO Replace R308
OK
Check D301
YES
NO Replace D301
Check R328
YES
NO Replace R328
Check Q302 output
12V
YES
Check ECO-POWER
is “HIHGT”
YES
NO NO Check or replace
R305,R303,Q301
OK
Check F301
YES
NO Replace F301
NO Refer to SMPS
troubleshooting (12V)
OK
6. U302/3.3V ABNORMAL

3-5
8. IC600 ABNORMAL
YES
Refer to power supply no 3.3V,
check or replace Q600
Check both end voltage Q600 (3.3V)
NO
YES
Check IC606 pin1 is “H”,
Check or replace Q601
Check Q601 is “H”
NO
YES
Check or replace L600 Check IC604 pin13 is 3.3V
NO
YES
Check or replace X601 Check IC600 pin1, 6 X601 operation
NO
OK
9. U654 ABNORMAL
NO
Check U654 pin1: CE,
pin6: SCK
YES
Check U654 pin2,5/SO,SI
YES
NO Replace U654
OK
NO Refer to 3.3V
troubleshooting
Check U654 pin8 VDD 3.3V
YES
OK
10. IC601 ABNORMAL
NO
Check IC601 pin34: CLK
pin35 CKE
YES
Check MCU IC603
YES
NO Replace MCU
OK
NO Refer to MCU
troubleshooting
Check MCU IC603
voltage 1.2V
YES
OK

3-6
11. U503 ABNORMAL
YES
Refer to power circuit troubleshooting Check the power supply to U503 pin24
NO
YES
Check JK601 pin47, 48 Vol_CLK/Vol_Data Check the SCL/SDA data of U503 pin25, 26
NO
YES
Check or replace U503 Check the control function
NO
OK
12. U501 ABNORMAL
NO
YES
Refer to power supply
U302 3.3V
LCD display check
Check the power
supply to U501 pin7
YES
NO Check MICOM U603 pin71
CS, pin72 DAT, pin73 WR
Check U501 pin1 CS
pin3 WR, pin4 data
YES
NO Replace MICOM
YES
OK
13. U101 FM TUNER MODULE
YES
Check Q305 B “High” Check the power supply of U101 pin3
NO
YES
Check JK600 pin24, 26 Check TU-SCL, TU-SDA
NO
YES
OK
Check the operation

3-7
14. CD PART
YES
Check R730,R731Check Open/Close
YES
Check “READING” display
Check CN703
Check CN703
YES
Turn on CD
YES
Check Reading OK
Check pickup movement
YES
Check U704 BA5927FM
YES
Check U703
YES
YES
Playing, check audio output
Check U703 pin55, 57
OK
NO
Check JK500/JK501
pin34(Open 3.3V Close 0V)
NO
NO
NO
NO
15. CD READING CHECK
NO
YES
Check CN723 pin6, 7
(SL+,SL-)
Check Connector locking
CN703, CN723
Does sled motor move?
YES
NO
Does the laser move?
YES
NO Defective pickup or
U703, U704
YES
NO Defective pickup or
U703, U704
Check CN703 pin1, 2
(F+,F-)
YES
NO
Does laser light?
YES
NO Defective pickup or Q701
Check CN703 pin19
(LD)
YES
NO
Does the spindle motor
rotate?
YES
NO Defective pickup or
U703, U704
Check CN723 pin8, 9
(SP+, SP-)
YES
Is reading ok? NO Defective pickup or
U703, U704
Check CN703 pin3, 4
(T+, T-)
NO

3-8
16. USB PART
NO
NO
Check “CHECKING”
or “USB” display
YES
OK
Check Power supply circuit
Q316 USB+5V
Turn on the USB
Check connector locking
CN401, CN705
NO
NONO
Check reading
YES
Check CN705
pin3, 4 (D+, D-)
Check CN401
pin2_5V
NONO
Playing,
Check audio output
YES
Check U503 pin3, 4
Check U703
pin55, 57
YES
NO
NO
Check SMPS power
supply
NO
Check Power supply
circuit Q308
Check Power supply
circuit Q302
Check F301
YES Replace Q308
YES Replace Q302
YES Replace F301
NO
Check MICOM IC603
pin116, 117 (D+, D-)

3-9
1. SPINDLE DRIVE AND MOTOR WAVEFORM
WAVEFORMS OF MAJOR CHECK POINT
SL-
SL+
SP-
SP+
U704 pin19 1
U704 pin20 2
U704 pin22 3
U704 pin21 4
TE
EE
FE
SP+
U703 pin62 5
U703 pin61 6
U703 pin60 7
U704 pin21 8
2. WHEN CD PLAYING FE/EE/TE/SP+ WAVEFORM