LG 37LH4000 Schematic

LCD TV

SERVICE MANUAL

CAUTION

BEFORE SERVICING THE CHASSIS, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

CHASSIS : LD91G

MODEL : 37LH4000

37LH4000-ZA

North/Latin America http://aic.lgservice.com Europe/Africa http://eic.lgservice.com Asia/Oceania http://biz.lgservice.com

Internal Use Only

Printed in KoreaP/NO : MFL58858403 (0903-REV01)

Only for training and service purposes

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CONTENTS

CONTENTS .............................................................................................. 2

PRODUCT SAFETY ..................................................................................3

SPECIFICATION ........................................................................................6

ADJUSTMENT INSTRUCTION .................................................................9

TROUBLE SHOOTING ............................................................................14

BLOCK DIAGRAM...................................................................................17

EXPLODED VIEW .................................................................................. 18

SVC. SHEET ...............................................................................................

Only for training and service purposes

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SAFETY PRECAUTIONS

Many electrical and mechanical parts in this chassis have special safety-related characteristics. These parts are identified by in the Schematic Diagram and Exploded View. It is essential that these special safety parts should be replaced with the same components as recommended in this manual to prevent Shock, Fire, or other Hazards. Do not modify the original design without permission of manufacturer.

General Guidance

An isolation Transformer should always be used during the servicing of a receiver whose chassis is not isolated from the AC power line. Use a transformer of adequate power rating as this protects the technician from accidents resulting in personal injury from electrical shocks.

It will also protect the receiver and it's components from being damaged by accidental shorts of the circuitry that may be inadvertently introduced during the service operation.

If any fuse (or Fusible Resistor) in this TV receiver is blown, replace it with the specified.

When replacing a high wattage resistor (Oxide Metal Film Resistor, over 1W), keep the resistor 10mm away from PCB.

Keep wires away from high voltage or high temperature parts.

Before returning the receiver to the customer,

always perform an AC leakage current check on the exposed metallic parts of the cabinet, such as antennas, terminals, etc., to be sure the set is safe to operate without damage of electrical shock.

Leakage Current Cold Check(Antenna Cold Check)

With the instrument AC plug removed from AC source, connect an electrical jumper across the two AC plug prongs. Place the AC switch in the on position, connect one lead of ohm-meter to the AC plug prongs tied together and touch other ohm-meter lead in turn to each exposed metallic parts such as antenna terminals, phone jacks, etc. If the exposed metallic part has a return path to the chassis, the measured resistance should be between 1MΩ and 5.2MΩ. When the exposed metal has no return path to the chassis the reading must be infinite. An other abnormality exists that must be corrected before the receiver is returned to the customer.

Leakage Current Hot Check (See below Figure)

Plug the AC cord directly into the AC outlet.

Do not use a line Isolation Transformer during this check.

Connect 1.5K/10watt resistor in parallel with a 0.15uF capacitor between a known good earth ground (Water Pipe, Conduit, etc.) and the exposed metallic parts. Measure the AC voltage across the resistor using AC voltmeter with 1000 ohms/volt or more sensitivity. Reverse plug the AC cord into the AC outlet and repeat AC voltage measurements for each exposed metallic part. Any voltage measured must not exceed 0.75 volt RMS which is corresponds to

0.5mA. In case any measurement is out of the limits specified, there is possibility of shock hazard and the set must be checked and repaired before it is returned to the customer.

Leakage Current Hot Check circuit

1.5 Kohm/10W

To Instrument's exposed METALLIC PARTS

Good Earth Ground such as WATER PIPE, CONDUIT etc.

AC Volt-meter

When 25A is impressed between Earth and 2nd Ground for 1 second, Resistance must be less than 0.1

*Base on Adjustment standard

IMPORTANT SAFETY NOTICE

0.15uF

Ω

Only for training and service purposes

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CAUTION: Before servicing receivers covered by this service manual and its supplements and addenda, read and follow the

SAFETY PRECAUTIONS on page 3 of this publication. NOTE: If unforeseen circumstances create conflict between the

following servicing precautions and any of the safety precautions on page 3 of this publication, always follow the safety precautions. Remember: Safety First.

General Servicing Precautions

1. Always unplug the receiver AC power cord from the AC power source before; a. Removing or reinstalling any component, circuit board

module or any other receiver assembly.

b. Disconnecting or reconnecting any receiver electrical plug or

other electrical connection.

c. Connecting a test substitute in parallel with an electrolytic

capacitor in the receiver. CAUTION: A wrong part substitution or incorrect polarity installation of electrolytic capacitors may result in an explosion hazard.

2. Test high voltage only by measuring it with an appropriate high voltage meter or other voltage measuring device (DVM, FETVOM, etc) equipped with a suitable high voltage probe. Do not test high voltage by "drawing an arc".

3. Do not spray chemicals on or near this receiver or any of its assemblies.

4. Unless specified otherwise in this service manual, clean electrical contacts only by applying the following mixture to the contacts with a pipe cleaner, cotton-tipped stick or comparable non-abrasive applicator; 10% (by volume) Acetone and 90% (by volume) isopropyl alcohol (90%-99% strength) CAUTION: This is a flammable mixture. Unless specified otherwise in this service manual, lubrication of contacts in not required.

5. Do not defeat any plug/socket B+ voltage interlocks with which receivers covered by this service manual might be equipped.

6. Do not apply AC power to this instrument and/or any of its electrical assemblies unless all solid-state device heat sinks are correctly installed.

7. Always connect the test receiver ground lead to the receiver chassis ground before connecting the test receiver positive lead. Always remove the test receiver ground lead last.

8. Use with this receiver only the test fixtures specified in this

service manual.

CAUTION: Do not connect the test fixture ground strap to any heat sink in this receiver.

Electrostatically Sensitive (ES) Devices

Some semiconductor (solid-state) devices can be damaged easily by static electricity. Such components commonly are called Electrostatically Sensitive (ES) Devices. Examples of typical ES 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 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 to prevent potential shock reasons prior to applying power to the

unit under test.

2. After removing an electrical assembly equipped with ES 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 ES devices.

4. Use only an anti-static type solder removal device. Some solder removal devices not classified as "anti-static" can generate electrical charges sufficient to damage ES devices.

5. Do not use freon-propelled chemicals. These can generate electrical charges sufficient to damage ES devices.

6. Do not remove a replacement ES device from its protective package until immediately before you are ready to install it. (Most replacement ES devices are packaged with leads electrically shorted together by conductive foam, aluminum foil or comparable conductive material).

7. Immediately before removing the protective material from the leads of a replacement ES device, touch the protective material to the chassis or circuit assembly into which the device will be installed. CAUTION: Be sure no power is applied to the chassis or circuit, and observe all other safety precautions.

8. Minimize bodily motions when handling unpackaged replacement ES 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 ES device.)

General Soldering Guidelines

1. Use a grounded-tip, low-wattage soldering iron and appropriate tip size and shape that will maintain tip temperature within the range or 500

°F to 600°F.

2. Use an appropriate gauge of RMA resin-core solder composed of 60 parts tin/40 parts lead.

3. Keep the soldering iron tip clean and well tinned.

4. Thoroughly clean the surfaces to be soldered. Use a mall wirebristle (0.5 inch, or 1.25cm) brush with a metal handle. Do not use freon-propelled spray-on cleaners.

5. Use the following unsoldering technique a. Allow the soldering iron tip to reach normal temperature.

(500

°F to 600°F)

b. Heat the component lead until the solder melts. c. Quickly draw the melted solder with an anti-static, suction-

type solder removal device or with solder braid. CAUTION: Work quickly to avoid overheating the circuit board printed foil.

6. Use the following soldering technique. a. Allow the soldering iron tip to reach a normal temperature

(500

°F to 600°F)

b. First, hold the soldering iron tip and solder the strand against

the component lead until the solder melts.

c. Quickly move the soldering iron tip to the junction of the

component lead and the printed circuit foil, and hold it there only until the solder flows onto and around both the component lead and the foil. CAUTION: Work quickly to avoid overheating the circuit board printed foil.

d. Closely inspect the solder area and remove any excess or

splashed solder with a small wire-bristle brush.

SERVICING PRECAUTIONS

Only for training and service purposes

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IC Remove/Replacement

Some chassis circuit boards have slotted holes (oblong) through which the IC leads are inserted and then bent flat against the circuit foil. When holes are the slotted type, the following technique should be used to remove and replace the IC. When working with boards using the familiar round hole, use the standard technique as outlined in paragraphs 5 and 6 above.

Removal

1. Desolder and straighten each IC lead in one operation by gently prying up on the lead with the soldering iron tip as the solder melts.

2. Draw away the melted solder with an anti-static suction-type solder removal device (or with solder braid) before removing the IC.

Replacement

1. Carefully insert the replacement IC in the circuit board.

2. Carefully bend each IC lead against the circuit foil pad and solder it.

3. Clean the soldered areas with a small wire-bristle brush. (It is not necessary to reapply acrylic coating to the areas).

"Small-Signal" Discrete Transistor Removal/Replacement

1. Remove the defective transistor by clipping its leads as close as possible to the component body.

2. Bend into a "U" shape the end of each of three leads remaining on the circuit board.

3. Bend into a "U" shape the replacement transistor leads.

4. Connect the replacement transistor leads to the corresponding leads extending from the circuit board and crimp the "U" with long nose pliers to insure metal to metal contact then solder each connection.

Power Output, Transistor Device Removal/Replacement

1. Heat and remove all solder from around the transistor leads.

2. Remove the heat sink mounting screw (if so equipped).

3. Carefully remove the transistor from the heat sink of the circuit board.

4. Insert new transistor in the circuit board.

5. Solder each transistor lead, and clip off excess lead.

6. Replace heat sink.

Diode Removal/Replacement

1. Remove defective diode by clipping its leads as close as possible to diode body.

2. Bend the two remaining leads perpendicular y to the circuit board.

3. Observing diode polarity, wrap each lead of the new diode around the corresponding lead on the circuit board.

4. Securely crimp each connection and solder it.

5. Inspect (on the circuit board copper side) the solder joints of the two "original" leads. If they are not shiny, reheat them and if necessary, apply additional solder.

Fuse and Conventional Resistor Removal/Replacement

1. Clip each fuse or resistor lead at top of the circuit board hollow stake.

2. Securely crimp the leads of replacement component around notch at stake top.

3. Solder the connections. CAUTION: Maintain original spacing between the replaced component and adjacent components and the circuit board to prevent excessive component temperatures.

Circuit Board Foil Repair

Excessive heat applied to the copper foil of any printed circuit board will weaken the adhesive that bonds the foil to the circuit board causing the foil to separate from or "lift-off" the board. The following guidelines and procedures should be followed whenever this condition is encountered.

At IC Connections

To repair a defective copper pattern at IC connections use the following procedure to install a jumper wire on the copper pattern side of the circuit board. (Use this technique only on IC connections).

1. Carefully remove the damaged copper pattern with a sharp knife. (Remove only as much copper as absolutely necessary).

2. carefully scratch away the solder resist and acrylic coating (if used) from the end of the remaining copper pattern.

3. Bend a small "U" in one end of a small gauge jumper wire and carefully crimp it around the IC pin. Solder the IC connection.

4. Route the jumper wire along the path of the out-away copper pattern and let it overlap the previously scraped end of the good copper pattern. Solder the overlapped area and clip off any excess jumper wire.

At Other Connections

Use the following technique to repair the defective copper pattern at connections other than IC Pins. This technique involves the installation of a jumper wire on the component side of the circuit board.

1. Remove the defective copper pattern with a sharp knife. Remove at least 1/4 inch of copper, to ensure that a hazardous condition will not exist if the jumper wire opens.

2. Trace along the copper pattern from both sides of the pattern break and locate the nearest component that is directly connected to the affected copper pattern.

3. Connect insulated 20-gauge jumper wire from the lead of the nearest component on one side of the pattern break to the lead of the nearest component on the other side. Carefully crimp and solder the connections. CAUTION: Be sure the insulated jumper wire is dressed so the it does not touch components or sharp edges.

Only for training and service purposes

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SPECIFICATION

NOTE : Specifications and others are subject to change without notice for improvement

4. Electrical specification

4.1 Module General Specification

1. Application range

This specification is applied to the LCD TV used LD91G chassis.

2. Requirement for Test

Each part is tested as below without special appointment.

1) Temperature : 25±5ºC (77±9ºF), CST : 40±5ºC

2) Relative Humidity : 65±10%

3) Power Voltage : Standard input voltage (100-240V@50/60Hz) * Standard Voltage of each products is marked by models.

4) Specification and performance of each parts are followed

each drawing and specification by part number in accordance with BOM.

5) The receiver must be operated for about 5 minutes prior to

the adjustment.

3. Test method

1) Performance: LGE TV test method followed

2) Demanded other specification

- Safety: CE, IEC specification

- EMC:CE, IEC

No Item Specification Remark

1 Screen Device 37” wide color display module LCD

2 Aspect Ratio 16:9

3 LCD Module 37” TFT LCD FHD LGD

4 Storage Environment Temp. : -20 ~ 60 deg

Humidity : 10 ~ 90 %

5 Input Voltage AC100-240V~, 50/60Hz

6 Power Consumption Typ : 133.28, Max : 142.76 FHD

7 Module Size 877.0 (H) x 516.8 (V) x 55.5 (D)

8 Pixel Pitch 0.42675 mm(D)

9 Back Light EEFL

10 Display Colors 1.06Billion(FHD LGD),16.7M (others)

11 Coating 3H, AG

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Only for training and service purposes

5. Chroma& Brightness

5.1 Module optical specification

1) Standard Test Condition (The unit has been ‘ON’)

2) Stable for approximately 30 minutes in a dark environment at 25±2°…

3) The values specified are at approximate distance 50Cm from the LCD surface

4) Ta=25±2°C, VLCD=12.0V, fV=60Hz, Dclk=74.25MHz VBR_A=1.65V,ExtVBR_B=100%

No. Item Specification Min. Typ. Max. Remark

1. Viewing Angle<CR>10> Right/Left/Up/Down 178 Degree

2. Luminance Luminance (cd/m

) 400 500

Variation - 1.3 MAX /MIN

3. Contrast Ratio CR 1000 1400

4. CIE Color Coordinates White Wx 0.279

Wy 0.292 Typ

RED Xr 0.639 ±0.03

Yr 0.334

Green Xg 0.289

Yg 0.606

Blue Xb 0.145

Yb 0.065

6. Component Video Input (Y, CB/PB, CR/PR)

Specification

Remark

Resolution H-freq(kHz) V-freq(Hz)

1. 720x480 15.73 60.00 SDTV,DVD 480i

2. 720x480 15.63 59.94 SDTV,DVD 480i

3. 720x480 31.47 59.94 480p

4. 720x480 31.50 60.00 480p

5. 720x576 15.625 50.00 SDTV,DVD 625 Line

6. 720x576 31.25 50.00 HDTV 576p

7. 1280x720 45.00 50.00 HDTV 720p

8. 1280x720 44.96 59.94 HDTV 720p

9. 1280x720 45.00 60.00 HDTV 720p

10. 1920x1080 31.25 50.00 HDTV 1080i

11. 1920x1080 33.75 60.00 HDTV 1080i

12. 1920x1080 33.72 59.94 HDTV 1080i

13. 1920x1080 56.250 50 HDTV 1080p

14. 1920x1080 67.5 60 HDTV 1080p

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Only for training and service purposes

Specification

Proposed Remark

Resolution H-freq(kHz) V-freq(Hz) Pixel Clock(MHz)

1. 720*400 31.468 70.08 28.321 For only DOS mode

2. 640*480 31.469 59.94 25.17 VESA

Input 848*480

60Hz, 852*480 60Hz

-> 640*480 60Hz Display

3. 800*600 37.879 60.31 40.00 VESA

4. 1024*768 48.363 60.00 65.00 VESA(XGA)

5. 1280*768 47.78 59.87 79.5 WXGA

6. 1360*768 47.72 59.8 84.75 WXGA

7. 1366*768 47.56 59.6 84.75 WXGA

8. 1280*1024 63.595 60.0 108.875 SXGA FHD model

9. 1600*1200 74.07 59.98 130.375 UXGA FHD model

10. 1280*720 45 60 74.25 720P DTV Standard

11. 1920*1080 66.647 59.988 138.625 WUXGA FHD model

7. RGB (PC)

8. HDMI Input (PC/DTV)

(1) DTV Mode

No Resolution H-freq(kHz) V-freq.(Hz) Pixel clock(MHz) Proposed Remark

1. 720*400 31.468 70.08 28.321 HDCP

2. 640*480 31.469 59.94 25.17 VESA HDCP

3. 800*600 37.879 60.31 40.00 VESA HDCP

4. 1024*768 48.363 60.00 65.00 VESA(XGA) HDCP

5. 1280*768 47.78 59.87 79.5 WXGA HDCP

6. 1360*768 47.72 59.8 84.75 WXGA HDCP

7. 1366*768 47.56 59.6 84.75 WXGA HDCP

8. 1280*1024 63.595 60.0 108.875 SXGA HDCP

9. 1600*1200 74.07 59.98 130.375 UXGA HDCP

10. 1920*1080 66.647 59.988 138.625 WUXGA HDCP

(2) PC Mode

No Resolution H-freq(kHz) V-freq.(Hz) Pixel clock(MHz) Proposed Remark

1. 720*480 15.734 /15.6 59.94 /60 27.00 SDTV 480I

2. 720*480 31.469 /31.5 59.94 /60 27.00/27.03 SDTV 480P

3. 720*576 15.625 50 27(54) SDTV 576I

4. 720*576 31.25 50 54 SDTV 576P

5. 1280*720 37.500 50 74.25 HDTV 720P

6. 1280*720 44.96 /45 59.94 /60 74.17/74.25 HDTV 720P

7. 1920*1080 33.72 /33.75 59.94 /60 74.17/74.25 HDTV 1080I

8. 1920*1080 28.125 50.00 74.25 HDTV 1080I

9. 1920*1080 26.97 /27 23.97 /24 74.17/74.25 HDTV 1080P

10. 1920*1080 33.716 /33.75 29.976 /30.00 74.25 HDTV 1080P

11. 1920*1080 56.250 50 148.5 HDTV 1080P

12. 1920*1080 67.43 /67.5 59.94 /60 148.35/148.50 HDTV 1080P

+ 18 hidden pages