LG 42LH3800 Repair Manual

The LG 42LH3800 is a 42-inch LCD television featuring Full HD 1080p resolution, built-in digital and analog tuners, multiple HDMI inputs, USB connectivity, Smart TV functionality, and energy-efficient LED backlighting. This repair manual provides comprehensive guidance for troubleshooting, disassembly, component replacement, and maintenance procedures for qualified service technicians.

1. Safety Precautions 2. Technical Specifications 3. Disassembly Procedures 4. Component Identification 5. Troubleshooting Flowcharts 6. Power Supply Repair 7. Main Board Repair 8. LCD Panel Replacement 9. Backlight System 10. Test Points & Voltages 11. Reassembly Guidelines

Safety Precautions

Critical safety information for service technicians working on the LG 42LH3800 television.

Hazard	Precaution
Electrical Shock	Disconnect power before servicing; discharge capacitors
High Voltage	Inverter section contains lethal voltages; use insulated tools
ESD Protection	Use anti-static wrist strap when handling circuit boards
LCD Panel	Handle with care; glass is fragile and easily damaged
Backlight System	LED arrays contain high brightness sources; avoid direct eye exposure
Chemical Hazards	Some components may contain hazardous materials; proper disposal required

Technical Specifications

Detailed technical specifications for the LG 42LH3800 LCD television.

Model: 42LH3800
Screen Size: 42 inches diagonal
Resolution: 1920 x 1080 Full HD
Backlight: LED Edge Lit
Power Supply: 100-240V AC, 50/60Hz
Power Consumption: 65W typical, 0.3W standby
Inputs: 3x HDMI, 2x USB, Component, Composite, RF
Outputs: Optical Audio, Headphone
Smart TV: WebOS 2.0 with Wi-Fi connectivity
Dimensions: 37.8" x 22.4" x 2.8" (without stand)
Weight: 22.5 lbs (without stand)

Disassembly Procedures

Step-by-step disassembly instructions for accessing internal components.

Remove Stand: Lay TV face down on soft surface; remove 4 screws securing stand.
Remove Rear Cover: Remove all visible screws from rear casing; carefully separate halves.
Disconnect Cables: Note cable positions; disconnect power supply, main board, and panel cables.
Remove Main Board: Remove mounting screws; carefully lift board from chassis.
Access Power Supply: Remove screws securing power supply board; disconnect all connectors.
LCD Panel Removal: Remove bezel screws; carefully separate LCD panel from frame.

WARNING! Always disconnect power before disassembly. Handle LCD panel with extreme care.

Component Identification

Identification and location of major components within the LG 42LH3800.

Component	Location	Part Number
Main Board	Center rear	EAY62819301
Power Supply	Left side	EAY62819401
LED Driver	Right side	EAY62819501
T-Con Board	Top center behind panel	6870C-0596A
Wi-Fi Module	Attached to main board	6841T-1011A
IR Sensor Board	Bottom bezel center	EBT62870001
Speaker Assembly	Bottom left and right	EMK46800101

Troubleshooting Flowcharts

Systematic troubleshooting procedures for common failure modes.

No Power: Check AC input → Fuse → Standby voltage → Main power supply
No Backlight: Verify main board operation → Check LED driver voltages → Test LED strips
No Picture/Sound: Test inputs → Check main board voltages → Verify T-con operation
Intermittent Operation: Check for loose connections → Test capacitors → Monitor temperatures
Smart TV Issues: Verify network connection → Check Wi-Fi module → Test main board memory

Power Supply Repair

Diagnosis and repair procedures for the power supply board.

Symptom	Test Point	Expected Value
No standby LED	STBY 3.3V	3.3V ±5%
No power on	PS_ON signal	3.3V when powered
No backlight	BL_ON signal	3.3V when enabled
Dim picture	LED voltage	120V DC typical
Audio distortion	12V audio supply	12V ±5%

Common Failures: Primary capacitors, switching transistors, rectifier diodes, fuse.

Main Board Repair

Troubleshooting and repair guidance for the main system board.

Power Sequence: Verify proper startup sequence and timing
Memory Testing: Check DDR memory operation and addressing
Processor Operation: Monitor main SoC temperatures and clock signals
Input/Output Testing: Verify all port functionality and signal integrity
Firmware Recovery: Procedures for firmware corruption and recovery

CAUTION! BGA components require specialized equipment for replacement.

LCD Panel Replacement

Procedures for safe LCD panel removal and replacement.

Remove all external covers and disconnect all cables
Carefully separate bezel from front assembly
Remove metal frame securing LCD panel
Lift panel straight up using suction cup handles
Clean optical films and inspect for damage
Install replacement panel in reverse order
Reconnect T-con cables and test before final assembly

WARNING! LCD panels are extremely fragile. Use proper handling equipment.

Backlight System

LED backlight system diagnosis and repair procedures.

Component	Test Procedure	Specification
LED Strips	Individual LED forward voltage	3.0-3.4V per LED
Driver Board	Output voltage and current	100-150V, 200-400mA
Optical Films	Visual inspection	No scratches or discoloration
Thermal Management	Temperature monitoring	Below 70°C operating

Test Points & Voltages

Critical test points and expected voltage measurements.

Main Power Input: 120V AC
Standby Supply: 3.3V STBY
Main 12V Supply: 12V ±5%
Main 5V Supply: 5V ±5%
LED Driver Output: 100-150V DC
T-Con VCC: 12V
T-Con VGH: 25V
T-Con VGL: -6V
Audio Amplifier: 15V

Reassembly Guidelines

Proper reassembly procedures to ensure correct operation and safety.

Verify all repairs are complete and components tested
Clean all optical surfaces before reassembly
Route cables properly to avoid pinching or interference
Secure all screws in proper sequence and torque
Verify ground connections are secure
Test full functionality before returning to customer
Perform final safety check and certification

Final Testing: Power on test, input verification, audio check, thermal monitoring.