LG 42LG70 Series Installation guide

42LG70
42LG70
Direct View LCD

LCD DV 42LG70
2Spring 2009
OUTLINE
OUTLINE
•BallastBoard
• Main Board
•T-CONBoard
Circuit Board Operation, Troubleshooting of :
• Switch mode Power Supply
Section 1
Section 2
Contact Information, Preliminary Matters, Specifications,
LCD Overview, General Troubleshooting Steps,
Signal Distribution, Disassembly Instructions and Voltages
• Ft Control Board

LCD DV 42LG70
3Spring 2009
42LG70 LCD Direct View Display
Section 1
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.
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.
Overview of Topics to be Discussed
Overview of Topics to be Discussed

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IMPORTANT SAFETY NOTICE
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
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.
Preliminary Matters (The Fine Print)
Preliminary Matters (The Fine Print)

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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 assembly by its edges only. When
repackaging a failed electronic control assembly in an anti-static bag, observe these same precautions.
REGULATORY INFORMATION
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.
ESD
ESD NOTICE NOTICE
(Electrostatic Static Discharge)
(Electrostatic Static Discharge)

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CONTACT INFORMATION
CONTACT INFORMATION
Customer Service (and Part Sales) [phone]
Technical Support (and Part Sales) [phone]
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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7Spring 2009
Safety & Handling Regulations
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…
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.
Checking Points to be Considered
Troubleshooting
SECTION 1:
SECTION 1: LCD OVERVIEW LCD OVERVIEW

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Basic Troubleshooting Steps
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 After carefully checking the symptom and determining the circuits to be
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 To further isolate the failure, check for the proper waveforms with the
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 The final step is to correct the problem. Be careful of ESD and make sure to
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.

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This section of the manual will discuss the specifications of the 42LG70
LCD Direct View Display Panel.
42LG70 Product Information
42LG70 Product Information

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10 Spring 2009
Basic Specifications
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
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
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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13 Spring 2009
TOP PORTION
BOTTOM PORTION
Remote Control Familiarization
Remote Control Familiarization

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14 Spring 2009
Accessing the Service Menu
Accessing the Service Menu
REMOTE
TOP PORTION
SIDE KEYS
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.
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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Side Input Jacks
Rear and Side Input Jacks
Rear and Side Input Jacks
Main PWB
Orientation
Rear Input Jacks

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16 Spring 2009
42LG70 Product Dimensions
42LG70 Product Dimensions

LCD DV 42LG70
17 Spring 2009
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.
DISASSEMBLY SECTION
DISASSEMBLY SECTION

LCD DV 42LG70
18 Spring 2009
Removing the Back Cover
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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19 Spring 2009
Power Supply PWB Removal
Power Supply PWB Removal
Disconnect P201, AC In
and P204.
Remove the 4 screws
indicated by the arrows.
P201
AC In
P204

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20 Spring 2009
Main PWB Shield Removal
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
arrows.
TAPE
TAPE
Decorative
Plastic
TAPE
Under
Plastic