LG LH-T6745 Service Manual

DVD/CD RECEIVER

SERVICE MANUAL

MODEL: LH-T6745

LH-T6745D
LHS-T6745C, LHS-T6745W, LHS-T6745T

SERVICE MANUAL LH-T6745 (LH-T6745D LHS-T6745C, LHS-T6745W, LHS-T6745T)

CD-R/RW

- 1-1 -

[CONTENTS]

❍ SECTION 1.GENERAL

• SERVICING PRECAUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

• ESD PRECAUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

• SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-5

❍ SECTION 2. AUDIO PART

• ELECTRICAL TROUBLESHOOTING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

• BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

• SCHEMATIC DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

• WIRNG DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

• PRINTED CIRCUIT DIARGAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23

❍ SECTION 3.DVD PART

• DVD PART ELECTRICAL TROUBLESHOOTING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1

• DETAILS AND WAVEFORMS ON SYSTEM TEST AND DEBUGGING . . . . . . . . . . . . . . . . .3-8

• BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

• DVD PART SCHEMATIC DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-25

❍ SECTION 4. EXPLODED VIEWS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1

❍ SECTION 5. SPEAKER PART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-1

❍ SECTION 6. REPLACEMENT PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1

- 1-2 -

SECTION 1. GENERAL

❏ 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 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 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 let
contact fingers or other exposed skin.

Magnet

How to hold the pick-up

Conductive Sheet

Cotton swab

Pressure

Pressure

- 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 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 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 (1M Ω)

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.

Resistor
(1 Mohm)

Conductive
Sheet

Resistor
(1 Mohm)

Armband

- 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 sur-

face 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 -

❏ SPECIFICATIONS

- 1-6 -

MEMO

- 2-1 -

❏

ELECTRICAL TROUBLESHOOTING GUIDE

INSERT

POWER CORD.

TURN ON

THE RED LED?

IS POWER ON?

CHECK POWER PLUG

AND POWER SUPPLY CIRCUIT.

DOES INITIAL
READ WORK?

DOES IT PLAY?

YES

NO

YES

YES

OK

NO

YES

NO

NO

CHECK POWER SUPPLY CIRCUIT.

CHECK LASER CIRCUIT.

CHECK TRACKING SERVO CIRCUIT.

TURN POWER ON.

CHECK FOCUS CIRCUIT.

CHECK DISC.

DOES IT OUTPUT

AUDIO?

YES

NO

CHECK AUDIO CIRCUIT.

1. Power check flow

SECTION 2. AUDIO PART

- 2-2 -

2.AUDIO µ.COM CIRCUIT

POWER ON

Does it appear

DVD Error at

FLD?

Does AV 1/2, TV, AUDIO,

OPTICAL IN, COAXIAL IN, FM87.5

appear at FLD?

Check

Connector(PN902)if

is normally.

Check power part

of Main B/D.

Check oscillator

of x101.

Check if IC101

PIN1 is High.

Check if IC101
PIN11 is High.

Check if IC101 PIN

17, 46, 72, 90 is high

(5V).

Check if IC101
PIN26 is High.

Replace IC101.

Does CD/DVD
appear at FLD?

Reconnet it.

Refer to SMPS

OK.

Refer to oscillator

Circuit.

Check DVD Reset Waveform.

Check IC101 Reset Wavefrom.

Check 5V line.

Check Power dection Circuit.

Does LOADING
appear at FLD?

Does no Disc or

Time appear at FLD?

Check if DVD an Audio

Micom Interface is OK.

Check power.

Check DVD Module.

Check SMPS.

- 2-3 -

3.FRONT CIRCUIT (1/2)

POWER ON

TURN ON

THE GREEN LED?

IS DIGITRON

ON NORMALLY?

Check If

All Buttens

Are OK.

Check If

The volume is

OK.

Check If

The headphone

is OK.

Check If

The Remocon

is OK.

FRONT B/D OK.

When it is needed to reconnect FFC cable into PN103/PN104,
short ZD 902 + and screw(chassis GND) near to ZD902.

PN104 pins
PIN2 : -27.5V

PIN3 : -23.0V
PIN4 : 5.0V
PIN11 : -34.0V

Check IF

THE PN103/PN104

IS OK?

Check IF the

FRONT POWER

IS OK(*2)

RECONNECT.

(REFER TO NOTICE *1)

REFER TO SMPS PART.

Check IF

The VFD001 PINS

ARE OK.

CHECK PATTERN

AND RESOLDERING.

- 2-4 -

4.FRONT CIRCUIT (2/2)

Check if

The Power part of the

Front is OK.

Check if

The Power part of the

Front is OK.

Check if

R036~R040

OK.

Check if

PN104 pin13, 15

waveform OK.

Check if

R032, R033

OK.

REFER TO

MICOM CIRCUIT.

REPLACE

R036~R040.

REFER TO

POWER(SMPS).

REFER TO

POWER(SMPS).

REFER TO

MICOM CIRCUIT.

REPLACE

R032, R033.

Check if

the power part of the

Front is OK.

Check if

The PN104 pin17

is Low.

REFER TO

POWER (SMPS).

REFER TO

POWER (SMPS).

REFER TO

POWER (SMPS).

REFER TO

POWER (SMPS).

Check if

Headphone jack

in JK001 is OK.

REFER TO

MICOM CIRCUIT.

CHECK MAN B/D.

Check if

the power part of the

Front is OK.

Check if

the RMC001 volume

is OK(5V).

Check if

the Remocon

Waveform of the

PN104 pin7.

Replace RMC001.

Check RMC

Circuit.

❏ BLOCK DIAGRAM

2-5 2-6

2-7 2-8

❏ SCHEMATIC DIAGRAMS

• FRONT SCHEMATIC DIAGRAM

2-9 2-10

• MICOM SCHEMATIC DIAGRAM

2-11 2-12

• I//O SCHEMATIC DIAGRAM

2-13 2-14

• DSP SCHEMATIC DIAGRAM

2-15 2-16

• AMP SCHEMATIC DIAGRAM

2-17 2-18

• SMPS-WIDE SCHEMATIC DIAGRAM