LG 42LG70 Service Manual

42LG70

Direct View LCD

OUTLINE

Section 1

Section 2

Contact Information, Preliminary Matters, Specifications, LCD Overview, General Troubleshooting Steps, Signal Distribution, Disassembly Instructions and Voltages

Circuit Board Operation, Troubleshooting of :

• Switch mode Power Supply

•Ballast Board

• Main Board

•T-CON Board

• Ft Control Board

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Overview of Topics to be Discussed

42LG70 LCD Direct View Display

This Section will cover Contact Information and remind the Technician of Important Safety Precautions for the Customers Safety as well as the Technician and the Equipment.

Basic Troubleshooting Techniques which can save time and money sometimes can be overlooked. These techniques will also be presented.

Section 1

This Section will get the Technician familiar with the Disassembly, Identification and Layout of the LCD Display Panel.

At the end of this Section the Technician should be able to Identify the Circuit Boards and have the ability and knowledge necessary to safely remove and replace any Circuit Board or Assembly.

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Preliminary Matters (The Fine Print)

IMPORTANT SAFETY NOTICE

The information in this training manual is intended for use by persons possessing an adequate background in electrical equipment, electronic devices, and mechanical systems. In any attempt to repair a major Product, personal injury and property damage can result. The manufacturer or seller maintains no liability for the interpretation of this information, nor can it assume any liability in conjunction with its use. When servicing this product, under no circumstances should the original design be modified or altered without permission from LG Electronics. Unauthorized modifications will not only void the warranty, but may lead to property damage or user injury. If wires, screws, clips, straps, nuts, or washers used to complete a ground path are removed for service, they must be returned to their original positions and properly fastened.

CAUTION

To avoid personal injury, disconnect the power before servicing this product. If electrical power is required for diagnosis or test purposes, disconnect the power immediately after performing the necessary checks. Also be aware that many household products present a weight hazard. At least two people should be involved in the installation or servicing of such devices. Failure to consider the weight of an product could result in physical injury.

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(Electrostatic Static Discharge)

ESD

Today’s sophisticated electronics are electrostatic discharge (ESD) sensitive. ESD can weaken or damage the electronics in a manner that renders them inoperative or reduces the time until their next failure. Connect an ESD wrist strap to a ground connection point or unpainted metal in the product. Alternatively, you can touch your finger repeatedly to a ground connection point or unpainted metal in the product. Before removing a replacement part from its package, touch the anti-static bag to a ground connection point or unpainted metal in the product. Handle the electronic control repackaging a failed electronic control assembly in an anti-static bag, observe these same precautions.

REGULATORY INFORMATION

This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a residential installation. This equipment generates, uses, and can radiate radio frequency energy, and, if not installed and used in accordance with the instruction manual, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures: Reorient or relocate the receiving antenna; Increase the separation between the equipment and the receiver; Connect the equipment to an outlet on a different circuit than that to which the receiver is connected; or consult the dealer or an experienced radio/TV technician for help.

NOTICE

(Electrostatic Static Discharge)

assembly by its edges only. When

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CONTACT INFORMATION

Customer Service (and Part Sales) (800) 243-0000

Technical Support (and Part Sales) (800) 847-7597

USA Website (GCSC) aic.lgservice.com Customer Service Website us.lgservice.com

LG CS Academy lgcsacademy.com

LG Web Training lge.webex.com

Published March 2009 by LG Technical Support and Training

LG Electronics Alabama, Inc.

201 James Record Road,

Huntsville, AL, 35813.

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SECTION 1:

Safety & Handling Regulations

1. Approximately 20 minute pre-run time is required before any adjustments are performed.

2. Refer to the Voltage Sticker on the Switch Mode Power Supply silk screening. (+/- ½ volt).

3. Be cautious of electric shock from the Backlight section, it uses high voltage AC. Check that the Power Supply and Drive Circuits are completely discharged because of residual current stored before Circuit Board removal.

4. C-MOS circuits are sensitive to static electricity. Use caution when dealing with these IC and circuits.

5. Exercise care when making voltage and waveform checks to prevent costly short circuits from damaging the unit.

6. Be cautious of lost screws and other metal objects to prevent a possible short in the circuitry.

LCD OVERVIEW

Troubleshooting

Checking Points to be Considered

1. Check the appearance of the Replacement Panel and Circuit Boards for both physical damage and part number accuracy.

2. Check the model label. Verify model names and board model matches.

3. Check details of defective condition and history. Example: Oscillator failure dead set, etc…

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Basic Troubleshooting Steps

Define, Localize, Isolate and Correct

•Define Look at the symptom carefully and determine what circuits could be causing the failure. Use your senses Sight, Smell, Touch and Hearing. Look for burned parts and check for possible overheated components. Capacitors will sometimes leak dielectric material and give off a distinct odor. Frequency of power supplies will change with the load, or listen for relay closing etc. Observation of the front Power LED may give some clues.

•Localize checked and after giving a thorough examination using your senses the first check should always be the DC Supply Voltages to those circuits under test. Always confirm the supplies are not only the proper level but be sure they are noise free. If the supplies are missing check the resistance for possible short circuits.

•Isolate Oscilloscope to make a final determination of the failure. Look for correct Amplitude Phasing and Timing of the signals also check for the proper Duty Cycle of the signals. Sometimes “glitches” or “road bumps” will be an indication of an imminent failure.

•Correct check the DC Supplies for proper levels. Make all necessary adjustments and lastly always perform a Safety AC Leakage Test before returning the product back to the Customer.

After carefully checking the symptom and determining the circuits to be

To further isolate the failure, check for the proper waveforms with the

The final step is to correct the problem. Be careful of ESD and make sure to

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42LG70 Product Information

This section of the manual will discuss the specifications of the 42LG70

LCD Direct View Display Panel.

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Basic Specifications

• Full HD 1080p Resolution (1920 x 1080)

• 50,000:1 Dynamic Contrast Ratio

• TruMotion 120Hz

• 4x HDMI™ V.1.3 with Deep Color

• Intelligent Sensor

• 24p Real Cinema

• AV Mode (Cinema, Sports, Game)

• Clear Voice

• LG SimpLink™ Connectivity

• Invisible Speaker System

• USB 2.0 (JPEG, MP3)

• ISFccc

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Basic Specifications (LOGO Familiarization) Page 1

Full HD 1080p Resolution Displays HDTV programs in full 1920 x 1080p resolution for a more detailed picture.

TruMotion 120Hz

Advance 120Hz panel provides clear, smooth images, even during fast action scenes creating a stable structure for a crisper picture.

Intelligent Sensor

Unlike other sensors which can only sense brightness of ambient light, LG’s “Intelligent Sensor” uses 4,096 sensing steps to evaluate its surroundings. Using a sophisticated algorithm, the LG processes picture quality elements including brightness, contrast, color, sharpness and white balance. The result is a picture optimized for it’s surroundings, more pleasing to watch and which can also save up to 50% in power consumption.

24p Real Cinema

Hi-def movies run at exactly 24 frames per second speed that they were originally filmed in, making your home-cinema experience one step closer to a “Real Cinema” experience.

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Basic Specifications (LOGO Familiarization) Page 2

Clear Voice Technology

Automatically enhances and amplifies the sound of the human voice frequency range to provide high-quality dialogue when background noise swells.

SIMPLINK

Allows for convenient control of other LG SimpLink products using the existing HDMI connection.

Invisible Speaker System

A new invisible speaker system tuned by renowned audio expert, Mr. Mark Levinson. This unique system incorporates speaker actuators around the perimeter of the entire bezel, eliminating traditional speaker drivers and associated grills. This not only allows for a sleek, finished look, but also

offers a wider “sweet spot” by creating a virtual “wall” of sound.

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Remote Control Familiarization

TOP PORTION

BOTTOM PORTION

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Accessing the Service Menu

REMOTE

TOP PORTION

To access the Service Menu.

1) Turn the Set On

2) Simultaneously, Press and “Hold” the Menu Key on the Side Key pad and Press and “Hold” the Menu Key on the Remote approximately 5 seconds.

3) If Customer’s Menu appears, continue to hold until it disappears.

SIDE KEYS

4) The Service Menu appears

Note: It is possible, dependant upon the Software Version,

a Password may be required to enter the Service Menu.

If a password is required, enter

0000

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Rear and Side Input Jacks

Rear Input Jacks

Side Input Jacks

Main PWB

Orientation

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42LG70 Product Dimensions

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DISASSEMBLY SECTION

This section of the manual will discuss Disassembly, Layout and Circuit Board Identification, of the 42LG70 LCD Direct View Television.

Upon completion of this section the Technician will have a better understanding of the disassembly procedures, the layout of the printed circuit boards and be able to identify each board.

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Removing the Back Cover

The Stand does not need to be removed

Remove the 16 screws indicated.

Pay attention to the size and type of screw

as there are many different types.

Putting in the improper screw when

reassembling may Cause damage.

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Power Supply PWB Removal

Disconnect P201, AC In and P204.

Remove the 4 screws indicated by the arrows.

P201

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Main PWB Shield Removal

Remove the two screws holding the Decorative plastic piece on the right side. Remove the plastic piece.

Remove the two pieces of tape on the left side holding down the cables and the one at the top.

Remove the remaining 11 screws indicated by the

TAP

ast

arrows.

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MAIN PWB Removal

Disconnect P1000, P1001, P800, P404 and P501 Note: In the top right is a connector P200. This is an open connection.

Remove the 2 screws securing the Main PWB.

Note: The top 2 and bottom 2 screws were removed during the shield removal process.

P800

P404

P1000

P1001

P200

Upgrades

NOTE: Look carefully on

top and behind the BCM

and Micronas IC.

Look for a piece of

Chocolate

(Heat Transfer Material).

Be sure to transfer to new PWB if replaced.

P501

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CON (TFT Drive) PWB Removal

TT--CON (TFT Drive) PWB Removal

Remove the 2 screws at the top of each bracket. Remove the 3 Screws in the T-CON shield. Lift up the left bracket and work the shield out and off.

The three screws shown in the picture

below are for the Service Position.

They would already be removed in the

CN5 CN4

previous step.

Remove and save the tape over

the LVDS Cables

CN1

Disconnect CN1, CN2, CN4 and CN5.

See next slide for details.

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CN2

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CON (TFT DRIVE) PWB REMOVAL CONTINUED:

TT--CON (TFT DRIVE) PWB REMOVAL CONTINUED:

UNLOCKING CN1, CN2, CN4 and CN5

To remove the flex cables to the TFT Panel, CN4 or CN5: Place a soft sharp object like a fingernail underneath the black locking tab and gently lift upward.

(Shown by the arrows in Fig 1)

CN4 or CN5 Locked

Fig 1

Flip the lock up and back from the flex cable. Then the flex cable can be easily removed.

Unlocked

Fig 2

The locking tab is flipped upward

Fig 3

To remove the LVDS cables for CN1 or CN2; Press in on the two tabs and slowly rock the cable out of the connector.

(Shown by the arrows in Fig 3)

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TROUBLESHOOTING SECTION

This section of the manual will discuss troubleshooting. Upon completion of this section the Technician will have

a better understanding of how to diagnosis and resolve problems.

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+ 56 hidden pages

LG 42LG70 Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

OUTLINE

CONTACT INFORMATION

Basic Troubleshooting Steps

Rear Input Jacks