LG 42LK450 UB Service Manual

The LG 42LK450 UB is a 42-inch LCD television featuring Full HD 1080p resolution, built-in digital and analog tuners, multiple connectivity options including HDMI, USB, component and composite inputs, energy saving features, and advanced picture processing technologies. This service manual provides technical information for qualified service personnel including disassembly procedures, circuit diagrams, troubleshooting guides, and replacement part information.

1. Product Overview 2. Technical Specifications 3. Disassembly Instructions 4. Main Board Description 5. Power Supply Unit 6. LCD Panel Assembly 7. Troubleshooting Procedures 8. Test Patterns 9. Replacement Parts List 10. Wiring Diagrams 11. Safety Precautions

Product Overview

The LG 42LK450 UB features a 42-inch LCD panel with LED backlight technology, providing enhanced brightness and energy efficiency compared to traditional CCFL backlighting.

Component	Description
Main Board	EAX61759401 - Processes video/audio signals and controls TV functions
Power Supply	EAX61728801 - Provides regulated power to all components
T-Con Board	Controls timing and driving signals for LCD panel
LCD Panel	42-inch Full HD (1920x1080) LCD with LED backlight
Inverter Board	Drives LED backlight system
Control Board	Front panel buttons and IR receiver

Technical Specifications

Screen Size: 42 inches diagonal
Resolution: 1920 x 1080 pixels (Full HD)
Backlight: LED Edge-lit
TV System: ATSC/NTSC/QAM
Inputs: 3x HDMI, 2x USB, Component, Composite, PC Input
Sound Output: 10W + 10W (Stereo)
Power Consumption: 75W (typical), <0.5W (standby)
Power Supply: 100-240V AC, 50/60Hz
Dimensions: 38.2" x 24.4" x 3.3" (with stand)
Weight: 25.4 lbs (with stand)

Disassembly Instructions

Follow these steps carefully to disassemble the television for service.

Place TV face down on soft, clean surface with stand removed.
Remove all screws from rear cover using Phillips #2 screwdriver.
Carefully separate rear cover from main chassis starting from bottom.
Disconnect all cable connections between boards noting positions.
Remove metal shield by unscrewing mounting screws.
Access individual boards for testing or replacement.

WARNING! Disconnect power before disassembly. Handle LCD panel with care to avoid damage.

Main Board Description

The main board (EAX61759401) is the central processing unit of the television.

Connector	Function	Pin Count
CN201	Power Supply Input	10-pin
CN202	LVDS to T-Con Board	30-pin
CN203	Inverter Control	6-pin
CN204	Front Control Board	8-pin
CN205-CN207	HDMI Inputs	19-pin each
CN208	USB Ports	9-pin

IC Components: Main processor, memory, tuner, audio processor, HDMI receivers.

Power Supply Unit

The power supply board (EAX61728801) provides multiple voltage rails to system components.

Output	Voltage	Current Rating	Purpose
+12V	12V DC	4A	Audio amplifier, USB
+24V	24V DC	2.5A	LED backlight driver
+5V_STBY	5V DC	1A	Standby power
+5V	5V DC	3A	Main board logic
+3.3V	3.3V DC	2A	Processor/memory

Test Points: TP1 (+12V), TP2 (+24V), TP3 (+5V), TP4 (+3.3V), TP5 (GND)

LCD Panel Assembly

The LCD panel assembly includes the glass substrate, polarizers, and LED backlight system.

Panel Model: LC420EUN
Resolution: 1920 (H) x 1080 (V)
Pixel Pitch: 0.4845mm x 0.4845mm
Response Time: 5ms (Gray to Gray)
Viewing Angle: 178°/178° (H/V)
Backlight Life: 50,000 hours (typical)

LED Backlight Specifications: 48 LED strips, 6 LEDs per strip, operating voltage 24V DC

Troubleshooting Procedures

Systematic approach to diagnose and repair common issues.

Symptom	Possible Cause	Diagnostic Procedure
No Power	Power supply, main board	Check AC input, measure standby voltage, test power supply outputs
No Backlight	Inverter, LED strips	Check 24V supply, test inverter output, inspect LED connections
No Picture/Sound	Main board, power supply	Verify all voltages, check main board operation, test input signals
Distorted Picture	T-Con board, LVDS cable	Inspect LVDS connection, test T-Con voltages, replace T-Con board
No Sound	Audio circuit, speakers	Check audio IC, test speaker connections, verify audio settings

Test Patterns

Use these patterns to verify proper display operation after repair.

Color Bars: Verify color reproduction and uniformity
Gray Scale: Check backlight uniformity and gamma correction
Convergence: Verify pixel alignment and focus
Geometry: Check for distortion and linearity
Resolution: Confirm 1080p capability with fine patterns

Access Method: Service Menu > Test Pattern > Select Pattern

Replacement Parts List

Part Number	Description	Qty
EAX61759401	Main Board Assembly	1
EAX61728801	Power Supply Board	1
EAX61759301	T-Con Board	1
EAX61759201	Inverter Board	1
6871Q-0583A	Remote Control	1
10-37232-01	LED Backlight Strip	48
10-37233-01	LCD Panel Complete	1

Wiring Diagrams

Complete interconnection diagrams for all internal components.

Power Distribution: AC input to DC outputs routing
Signal Flow: Input sources to display processing
Control System: Microprocessor to peripheral control
Backlight Circuit: Inverter to LED strip connections
Audio System: Input to speaker output path

Note: Refer to separate schematic diagrams for detailed circuit information.

Safety Precautions

Critical safety information for service technicians.

Always disconnect AC power before servicing.
Use insulated tools when working with live circuits.
Discharge large capacitors before handling power supply.
Handle LCD panel with care to avoid breakage.
Use proper anti-static precautions when handling circuit boards.
Ensure all safety certifications are maintained after repair.
Verify proper grounding of all components during reassembly.

WARNING! High voltages are present in power supply and inverter circuits. Exercise extreme caution.