LG 42LH20 Series User manual

42LH20
42LH20
Direct View LCD
Original: March 2009
Updated: February 11, 2010

February 2009 42LH20
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OUTLINE
OUTLINE
• 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
• Side Keys

February 2009 42LH20
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42LH20 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)

LCD or PLASMA 2009 Model
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Contact Information
Contact Information
Also available on the
Also available on the
Plasma page
Plasma page New Training Materials on
New Training Materials on
the Learning Academy site
the Learning Academy site
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 Web Training lge.webex.com
LG CS Academy lgcsacademy.com
LG Electronics Alabama, Inc. 201
James Record Road, Huntsville,
AL, 35813.
http://136.166.4.200
Published March 2009 by LG Technical Support and Training
32LG40, 32LH30, 37LH55, 42LG60, 42LG70, 42LH20, 42LH40, 42LH50, 42LH90, 42SL80,
47LG90,47LH85
42PG20, 42PQ20, 42PQ30, 50PG20, 50PS80, 50PS60, 60PS11
LCD-DV:
PLASMA:
Plasma Panel
Alignment Handbook
Presentations
with Audio/Video
and Screen Marks

February 2009 42LH20
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Safety and Handling Regulations
1. Approximately 20 minute pre-run time is required before any adjustments are performed.
2. SMPS adjustments are factory sealed. They are VR301 (Frequency) and VR302 (Current)
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. Always handle the circuit boards on the
outside edges while using ESD protection.
5. Exercise care when making voltage and waveform checks to prevent costly short circuits
from damaging the unit.
6. Be cautious of loose screws and other metal objects to prevent a possible short in the
circuitry.
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…
Observe the following items
LCD Direct View Overview
LCD Direct View 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 Diode Check 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 42LH20
LCD Direct View Display Panel.
42LH20 Product Information
42LH20 Product Information

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Basic Specifications
Basic Specifications
Key Features
•42" Screen
•720p HD Resolution
•Two (2) HDMI(TM) (V.1.3 with Deep Color)
•ISFccc Ready
•Smart Energy Saving
•LG SimpLink (TM) (32-inch and above)
•LG Core Technologies (32-inch and above)
•Dynamic Contrast Ratio 12,000:1
•Response Time (G to G) 8ms
•Brightness 500 cd/m2
•Viewing Angle 178º / 178º
•Life Span (Typical) 60,000 hr
•Built-in Tuner ATSC/NTSC/Clear QAM
•HDMI™/HDCP Input 2 v1.3
•Cabinet Color Glossy Piano-Black
•Limited Warranty 1 Year Parts/Labor

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HD RESOLUTION 720p HD Resolution Pixels: 1365 (H) × 768 (V)
High definition television is the highest performance segment of the
DTV system used in the US. It’s a wide screen, high-resolution video
image, coupled with multi-channel, compact-disc quality sound.
FORMATS
480I
480P
1080I
720P
1080P
Interlaced
Progressive
Interlaced
Progressive
Progressive
Interlaced
2 Fields to make a Frame
Progressive
Each Field is a Frame
Think of sync as the Panels “Refresh Rate”
240 Lines
480 Lines
540 Lines
720 Lines
1080 Lines
NTSC
SD
HD
HD
HD
Possible Frame
Rates:
24FPS
30FPS
60FPS
BASIC
PIXEL COUNTS
720P Panel
1365 (H) ×768 (V)
1080P Panel
1920 (H) x 1080 (V)
Pixel Count Compared to Resolution
Pixel Count Compared to Resolution

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Basic Specifications (LOGO Familiarization) Page 1
Basic Specifications (LOGO Familiarization) Page 1
SIMPLINK
Allows for convenient control of other LG SimpLink products using the
existing HDMI connection.
Clear Voice Technology
Automatically enhances and amplifies the sound of the human voice
frequency range to provide high-quality dialogue when background noise
swells.

LCD or PLASMA 2009 Model
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TOP PORTION BOTTOM PORTION
Remote Control Familiarization
Remote Control Familiarization

LCD or PLASMA 2009 Model
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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: If a Password is required to enter the
Service Menu. Enter;
0000

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Rear and Side Input Jacks
Rear and Side Input Jacks
Main PWB
Orientation
Rear Input Jacks
USB Port
For Software
Upgrades Only

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1) Create an LG_DTV folder on the USB Flash Drive
2) Copy new software (xxx.epk) to "LG_DTV"
folder. Make sure to have correct software file.
3) With TV turned on, insert USB flash drive.
4) You can see the message
“TV Software Upgrade” (See figure to right)
5) Cursor left and highlight "START" Button and
push “Enter” button using the remote control.
6) You can see the download progress Bar.
7) Do not unplug until unit has automatically
restarted.
8) When download is completed, you will see
“COMPLETE”.
9) Your TV will be restarted automatically.
Software Upgrade Procedure
Software Upgrade Procedure
Shows the
Currently
Installed
Version
Shows the
Software
Version
found on the
USB Flash
Drive Shows the
Software file found
on the USB Flash
Drive
* CAUTION:
Do not remove AC power or the USB Flash Drive.
Do not turn off Power, during the upgrade
process.

42LH20 Dimensions
7-7/8"
200mm
25-11/16"
655mm
12-7/8"
327.5mm
40-3/8"
1028mm
Remove 4 screws to
remove stand for
wall mount
Model No.
Serial No.
Label
16-1/8"
410mm
20-1/16"
510mm
28-1/8"
715.4mm
3-3/8"
87.8mm
11-5/8"
297mm
Center
7-7/8"
200mm
3-9/16"
90mm
8-3/8"
223mm
9-1/16"
230mm
2-3/8"
60.4mm
Weight:
With Stand: 38.3 lbs / 17.4 kg
Without Stand: 32.3 lbs / 15.6 kg
There must be at least 4 inches of Clearance on all sides
42LH20 Product Dimensions
42LH20 Product Dimensions
17

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Disassembly:
This section of the manual will discuss Disassembly, Layout and Circuit
Board Identification, of the 42LH20 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.
Troubleshooting:
This section of the manual will also discuss troubleshooting.
Upon completion of this section the Technician will have a better understanding of
how to diagnosis and resolve problems.
DISASSEMBLY AND TROUBLESHOOTING SECTION
DISASSEMBLY AND TROUBLESHOOTING SECTION

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Removing the Back Step (1)
Removing the Back Step (1)
Remove the Stand by
Pulling it out of its
Retaining bracket.
Lay the TV down on its face. Remove the 4 screws
around stand indicated by the arrows.
Remove the one screw
hidden by the stand.
Reinsert the
stand and
stand the unit
upright for
service position
to continue
removing the
back cover.
Remove

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The Stand has to be removed first.
Remove the 22 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.
Remove the one screw hidden
under the stand.
See previous page.
Removing the Back Cover Step 2 (Stand has to be removed)
Removing the Back Cover Step 2 (Stand has to be removed)