LG 42LD520 Repair Manual

The LG 42LD520 is a 42-inch LCD television featuring Full HD 1080p resolution, built-in digital tuner, multiple HDMI inputs, USB connectivity, energy saving technology, and advanced picture processing. This repair manual provides comprehensive technical information for service technicians, including disassembly procedures, component specifications, troubleshooting guides, and safety precautions for proper maintenance and repair.

Safety Precautions

Before attempting any repairs, ensure proper safety measures are followed to prevent injury and equipment damage.

Hazard	Precaution
Electrical Shock	Disconnect power; discharge capacitors; use insulated tools
High Voltage	Inverter board carries lethal voltages; handle with care
ESD Protection	Use anti-static wrist strap; work on grounded surface
LCD Panel	Handle carefully; avoid pressure on screen surface
Backlight System	CCFL tubes contain mercury; dispose properly if broken
Hot Components	Allow cooling time; power supply components get hot

Technical Specifications

• Model: LG 42LD520
• Screen Size: 42 inches LCD
• Resolution: 1920 x 1080 Full HD
• Panel Type: IPS LCD
• Inputs: 4x HDMI, 2x USB, Component, Composite, PC Input
• Tuner: Digital/analog tuner
• Power Supply: 100-240V AC, 50/60Hz
• Power Consumption: 120W typical, 0.5W standby
• Dimensions: 1020 x 680 x 85 mm (with stand)
• Weight: 15.8 kg (with stand)

Disassembly Procedures

Step-by-step instructions for safe disassembly of the television unit.

1. Remove stand: Lay TV face down on soft surface; remove screws securing stand.
2. Remove rear cover: Remove all visible screws from rear casing; carefully separate cover.
3. Disconnect cables: Note cable positions; disconnect all internal connectors.
4. Remove main board: Remove mounting screws; lift board carefully.
5. Remove power supply: Disconnect all wires; remove mounting screws.
6. Access LCD panel: Remove bezel screws; carefully separate front assembly.

WARNING! Handle LCD panel with extreme care to avoid cracking or damaging the glass.

Component Identification

Key components and their functions within the television assembly.

Component	Part Number	Function
Main Board	EAX61719301	Signal processing, inputs, tuner
Power Supply	EAY61719201	AC/DC conversion, voltage regulation
LCD Panel	LC420EUN	Display assembly with drivers
Inverter Board	EAY61719401	Backlight power supply
T-Con Board	6870C-0598A	Timing control for LCD panel
IR Sensor Board	EAY61719501	Remote control reception

Troubleshooting Flowcharts

Systematic approach to diagnosing common problems.

1. No Power: Check AC input → Fuse → Standby voltage → Main power supply
2. No Picture/Sound: Verify input source → Check main board voltages → Test video processing
3. Backlight Issues: Test inverter output → Check CCFL connections → Replace backlight tubes
4. Image Problems: Test T-con board → Check LVDS cable → Verify panel voltages
5. Audio Problems: Check audio IC → Test speakers → Verify audio settings

Power Supply Repair

Detailed procedures for power supply board diagnosis and repair.

Test Point	Expected Voltage	Tolerance
Standby 5V	5.1V DC	±0.2V
Main 12V	12.0V DC	±0.5V
Main 24V	24.0V DC	±1.0V
Inverter Voltage	24V DC	±1.0V
Panel Voltages	Various	As marked

Common Failures: Fuse F101, IC201 (PWM controller), capacitors C205-C208

Main Board Repair

Main board component testing and replacement procedures.

1. Check all power rails: 3.3V, 1.8V, 1.2V, 5V
2. Test main processor: Check for overheating, reflow if necessary
3. Verify memory operation: Test DDR memory modules
4. Check video processor: Test HDMI inputs, component video
5. Test tuner section: Verify RF input, channel selection
6. Check audio section: Test audio IC, output amplifiers

Common Issues: BGA solder joints, failed memory, corrupted firmware

LCD Panel Replacement

Procedure for safe LCD panel removal and replacement.

1. Remove all external covers and components
2. Carefully disconnect LVDS cables from T-con board
3. Remove panel mounting screws and brackets
4. Lift panel straight up from frame assembly
5. Clean frame and prepare new panel
6. Install new panel and reassemble in reverse order

CAUTION! Never touch the LCD surface with bare hands; use clean gloves.

Backlight System

Backlight system components and maintenance procedures.

• Type: CCFL (Cold Cathode Fluorescent Lamp)
• Number of Lamps: 16 tubes
• Inverter Output: 800V AC @ 7mA per tube
• Lamp Life: 50,000 hours typical
• Replacement: Replace in sets for even brightness

Testing: Use CCFL tester; check for dark ends (aging lamps)

Software & Firmware

Firmware update procedures and software troubleshooting.

1. Current Version: 03.20.05
2. Update Method: USB download from LG service site
3. Recovery Mode: Hold Volume Down + Menu while powering on
4. Factory Reset: Menu → Settings → Reset to Initial Settings
5. Service Menu: Menu + Menu (remote) for 3 seconds

Note: Always backup settings before firmware updates

Test Points & Measurements

Critical test points for voltage and signal measurements.

Location	Measurement	Normal Value
TP201	Standby 5V	5.1V ±0.2V
TP202	Main 12V	12.0V ±0.5V
TP203	Main 24V	24.0V ±1.0V
TP301	LVDS Power	12.0V ±0.5V
TP302	Panel VCC	5.0V ±0.2V
TP401	Inverter Enable	3.3V when on

Service Support: LG Service Center 1-800-243-0000; www.lg.com