LG LHT-250-SC, LHT-252-SC Service manual

4.5 (4)

MANUAL SERVICE

T25-T250SC/LH-LH : MODELS 2SC

DVD/CD & KARAOKE RECEIVER

SERVICE MANUAL

MODELS : LH-T250SC(LH-T250SC)

[ Speakers: LHS-25SCS, LHS-25SCW ]

(LHMODELS-2SCT250SC): LH-T25

[ Speakers: LHS-25SCS, LHS-25SCW ]

[CONTENTS]

SECTION 1.GENERAL

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

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

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

SECTION 2. AUDIO PART

• AUDIO TROUBLESHOOTING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 2-1
• BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 2-4
• SCHEMATIC DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	2-6
• WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	2-18
• PRINTED CIRCUIT DIARGAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	2-20

SECTION 3.DVD & AMP PART

• ELECTRICAL TROUBLESHOOTING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	.3-1
• DVD PART SCHEMATIC DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	3-22

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

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

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

1-1

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.

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 let contact 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 this.

Pressure

Magnet

Pressure

How to hold the pick-up

Cotton swab

Conductive Sheet

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.

1-2

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.

Armband

Resistor

(1 Mohm)

Resistor

(1 Mohm)

Conductive

Sheet

1-3

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.

1-4

	SPECIFICATIONS
GENERAL
Power supply	Refer to main label
Power consumption	Refer to main label
Mass	2.5 kg
External dimensions (W x H x D)	360 x 56 x 310 mm
Operating conditions Temperature:	5°C to 35°C, Operation status: Horizontal
Operating humidity	5% to 85%
CD/DVD
Laser	Semiconductor laser, wavelength 650 nm
Signal system	PAL 625/50, NTSC 525/60
Frequency response (audio)	140 Hz to 20 kHz
Signal-to-noise ratio (audio)	More than 75 dB (1 kHz, NOP-3dB, 20 kHz LPF/A-Filter)
Dynamic range (audio)	More than 80 dB
Harmonic distortion (audio)	0.5 % (1 kHz, at 12W position) (20 kHz LPF/A-Filter)
Video output	1.0 V (p-p), 75 Ω, negative sync., RCA jack
TUNER
FM
Tuning Range	87.5 - 108.0 MHz or 65.0 - 74.0 MHz, 87.5 - 108.0 MHz
Intermediate Frequency	10.7 MHz
Signal-to Noise Ratio	60 dB (Mono)
Frequency Response	140 - 10,000 Hz
AM [MW]
Tuning Range	522 - 1,620 kHz or 520 - 1,720 kHz
Intermediate	Frequency 450 kHz

AMPLIFIER

Surround mode

(* Depending on the sound mode settings and the source, there may be no sound output.)

Outputs

Front: 30W + 30W (THD 10 %) Centre*: 30W

Surround*: 30W + 30W (6Ω at 1 kHz, THD 10 %) Subwoofer*: 70W (8Ω at 30 Hz, THD 10 %) MONITOR

MIC Jacks (ø3.5mm) (KARAOKE MODEL ONLY))

SPEAKERS
	Satellite Speaker (LHS-25SCS)	Passive Subwoofer (LHS-25SCW)
Type	1 Way 1 Speaker	1 Way 1 Speaker
Impedance	6 Ω	8 Ω
Frequency Response	160 - 20,000 Hz	65 - 1,500 Hz
Sound Pressure Level	84 dB/W (1m)	82 dB/W (1m)
Rated Input Power	30W	70W
Max. Input Power	60W	140W
Net Dimensions (W x H x D)	92 x 115 x 80 mm	160 x 350 x 280 mm
Net Weight	0.5 kg	3.18 kg