LG LFSU-850, LFU-850-D, LFU-850-A Service manual

MICRO HI-FI SYSTEM

SERVICE MANUAL

MODEL: LF-U850D, LF-U850A,

LFS-U850

SERVICE MANUAL MODEL: LF-U850D, LF-U850A, LFS-U850

CAUTION

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

- 1-1 -

[CONTENTS]

❍ SECTION 1.GENERAL

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

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

• SPECIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-5

❍ SECTION 2.ELECTRICAL SECTION

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

• INTERNAL BLOCK DIAGRAM of ICs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

• BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12

• SCHEMATIC DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14

• CD PART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20

• WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26

• PRINTED CIRCUIT BOARD DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-28

❍ SECTION 3. EXPLODED VIEWS

• CABINET AND MAIN FRAME SECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

• Deck Mechanism Exploded View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

❍ SECTION 4. SPEAKER PART

• MODEL:LFS-U850 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1

❍ SECTION 5. REPLACEMENT PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-1

- 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.

CLEARING MALFUNCTION

You can reset your unit to initial status if malfunction occur(button malfunction, display, etc.).
Using a pointed good conductor(such as driver), simply short the RESET jump wire on the inside of
the volume knob for more than 3 seconds.
If you reset your unit, you must reenter all its settings(stations, clock, timer)

NOTE: 1. To operate the RESET jump wire, pull the volume rotary knob and release it.

2. If you wish to operate the RESET jump wire, it is necessary to unplug the power cord.

Resistor
(1 Mohm)

Conductive
Sheet

Resistor
(1 Mohm)

Armband

RESET jump wire

VOLUME

VOLUME KNOB

DOWN

UP

- 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

MODEL

LF-U850D/A

SECTION

Power supply Refer to the back panel of the unit.

Power consumption 50 W

Mass 3.7 kg

Battery Operation 187 X 255 X 257 mm

Frequency response 40 - 18000 Hz

Signal-to-noise ratio 70 dB

Dynamic range 70 dB

Tuning Range 87.5 - 108.0 MHz or 65 - 74 MHz, 87.5 - 108.0 MHz

Intermediate Frequency 10.7 MHz

Signal to Noise Ratio 60/55 dB

Frequency Response 60 - 10000 Hz

Tuning Range 522 - 1620 kHz or 520 - 1720 kHz

Intermediate Frequency 450 kHz

Signal to Noise Ratio 34 dB

Frequency Response 120 - 2000 Hz

Output Power 80 W + 80 W

T.H.D 0.5 %

Frequency Response 42 - 20000 Hz

Signal-to-noise ratio 75 dB

Type Bass Reflex 3Way 4Speaker

Impedance 6 Ω

Frequency Response 60 - 20000 Hz

Sound Pressure Level 82 dB/W (1m)

Rated Input Power 80 W

Max. Input Power 160 W

Net Dimensions (WxHxD) 162x320x258 mm

Net Weight (1EA) 4.0 kg

[General][CD][Amp][Speakers]

[TUNER]

[AM] (MW)

[FM]

* Designs and specifications are subject to change without notice.

- 2-1 -

SECTION 2. ELECTRICAL SECTION

P-SENS PART CHECK

SMPS ASSY CN943 -> 4PIN 5V OPERATION CHECK

MAIN PCB PN101 4PIN 5V CHECK

MAIN PCB PN304 27PIN 5V CHECK

REFER TO SMPS TROUBLESHOOTING

❏ TROUBLESHOOTING GUIDE

YES

YES

NO

PN101 CONTACT STATUS CHECK

MAIN PCB PATTERN disconnection check

NO

FRONT CN304 7PIN 5V CHECK

YES

FRONT IC302 OPERATION AND INPUT VOLTAGE 4.7V~5.0V CHECK

YES

YES

U-COM 26PIN 5V CHECK

YES

IC302 INPUT VOLTAGE 4.7V OR ABOVE , OUTPUT VOLTAGE
3V OR ABOVE OPERATION CHECK

IC304 KIA7042 REPLACEMENT

NO

YES

VKK CHECK

CN943 6PIN DC -33V CHECK

MAIN PCB PN101 6PIN VOLTAGE -33V CHECK

REFER TO SMPS TROUBLESHOOTING

YES

YES

NO

MAIN PCB PATTERN DISCONNECTION CHECK

NO

PN304 3PIN VOLTAGE CHECK (-33V)

YES

FFC WIRE ASSEMBLY STATUS CHECK

NO

FRONT PCB CN304 3PIN VOLTAGE CHECK (-33V)

IC301 51PIN VOLTAGE CHECK

YES

FRONT PCB PATTERN DISCONNECTION CHECK

NO

- 2-2 -

U-COM 5V VOLTAGE CHECK

SMPS ASSY CN943 -> 3PIN 5V OPERATION CHECK

MAIN PCB PN101 3PIN 5VCHECK

REFER TO SMPS TROUBLESHOOTING

YES

NO

MAIN PCB PN304 5PIN 5.6VCHECK

PN101 CONTACT STATUS CHECK

YES

MAIN PCB PATTERN DISCONNECTION CHECK

YES

NO

FRONT CN304 29PIN 5.6V CHECK

FFC WIRE ASSEMBLY STATUS CHECK

YES

NO

U-COM 17,46,72,90PIN 4.7V~5V CHECK

FRONT PCB PATTERN DISCONNECTION CHECK

YES

NO

Q303 (A103S) BASE "HIGH" CHECK

Q301, Q302,Q502,Q503(D1304S) BASE "HIGH" CHECK

C-COM 10PIN (HIGH) OPERATION STATUS CHECK

YES

IC603(CS5340) 10PIN,12PIN INPUT CHECK

IC603(CS5340) 2PIN (MCLK), 4PIN (SDOUT), 7PIN
(SCLK), 8PIN (LRCK) OUTPUT WAVEFORM CHECK

YES

Q303(A103S)OPERATION STATUS CHECK

YES

REPLACE Q303(A103S) IF FAULTY

YES

MUTE

YES

NO

REPLACE EACH APPROPRIATE TR

NO

C-COM 10PIN LINE CHECK AND U-COM
REPLACEMENT

NO

MUTING CIRCUIT TROUBLESHOOTING (ON MUTE CONDITION)

HEAD PHONE MUTE CHECK

- 2-3 -

FUNCTION INPUT UNFELT (IC601 BU4052)

CD FUNCTION

IC601 (BU4052)5,14PIN INPUT WAVEFORM CHECK

NORMAL OPERATION

U-COM (IC301)83PIN,84PIN COMMUNICATION CHECK.

MUTING MODE CHECK IC301 REPLACEMENT

C601 (BU4052)16PINVDD,8PIN VSS POWER CHECK

REPLACE APPROPRIATE PARTS

YES

YES

YES

YES

NORMAL

REPLACE APPROPRIATE PARTS

YES

YES

NORMAL

NORMAL

IC602 (MC4580) 4PIN VSS,8PIN VDD POWER CHECK.

REFER TO SMPS
TROUBLESHOOTING

PN805 ASSEMBLY STATUS CHECK

YES

IC602 (MC4580) 2,6PIN INPUT WAVEFORM CHECK

YES

NO

NO

IC601 (BU4052)3,13PIN OUTPUT WAVEFORM CHECK

YES

NO

YES

FRONT CN304 MAIN PCB PN302 FFC WIRE
contact and assembly status check

NO

REPLACE FAULTY PARTS

- 2-4 -

AUX FUNCTION

IC601 (BU4052)4,11PIN INPUT WAVEFORM CHECK

NORMAL OPERATION

U-COM (IC301)83PIN,84PIN COMMUNICATION CHECK.

MAIN PCB PATTERN DISCONNECTION CHECK

IC601 (BU4052)16PINVDD,8PIN VSS POWER
CHECK

REPLACE APPROPRIATE PARTS

YES

YES

YES

YES

NORMAL

REPLACE APPROPRIATE PARTS

YES

YES

NORMAL

NORMAL

IC602 (MC4580) 4PIN VSS,8PIN VDD POWER
CHECK.

REFER TO SMPS
TROUBLESHOOTING

JK601 CONTACT STATUS CHECK

YES

IC602 (MC4580) 2,6PIN INPUT WAVEFORM CHECK

YES

NO

NO

IC601 (BU4052)3,13PIN OUTPUT WAVEFORM
CHECK

YES

NO

YES

FRONT CN304 MAIN PCB PN302 FFC
WIRE contact and assembly

NO

REPLACE FAULTY PARTS

- 2-5 -

TUNER FUNCTION

IC601 (BU4052)2,15PIN INPUT WAVEFORM CHECK

NORMAL OPERATION

U-COM (IC301)83PIN,84PIN COMMUNICATION
CHECK.

Refer to TUNER Troubleshooting and check power (2PIN12Vcheck)

IC601 (BU4052)16PINVDD,8PIN VSS POWER CHECK

REPLACE APPROPRIATE PARTS

YES

YES

YES

YES

NORMAL

REPLACE APPROPRIATE PARTS

YES

YES

NORMAL

NORMAL

IC602 (MC4580) 4PIN VSS,8PIN VDD POWER
CHECK.

REFER TO SMPS
TROUBLESHOOTING

TUNER MODULE (TU601) OPERATION CHECK

YES

IC602 (MC4580) 2,6PIN INPUT WAVEFORM CHECK

YES

NO

NO

IC601 (BU4052)3,13PIN OUTPUT WAVEFORM CHECK

YES

NO

YES

FRONT CN304 MAIN PCB PN302 FFC WIRE
CONTACT AND ASSEMBLY STATUS CHECK

NO

REPLACE FAULTY PARTS