LG Model LMX25981ST Repair Manual

The LG Model LMX25981ST is a high-performance appliance requiring specialized repair knowledge. This manual provides comprehensive technical information for qualified service technicians, including safety procedures, component identification, diagnostic troubleshooting, disassembly/reassembly instructions, and parts replacement guidelines. Below are key sections covering essential repair and maintenance procedures.

1. Safety Precautions & Warnings 2. Model Identification & Specifications 3. Tools & Test Equipment Required 4. Component Location & Diagrams 5. Diagnostic Flowcharts & Error Codes 6. Disassembly Procedure 7. Troubleshooting Common Faults 8. Parts List & Replacement 9. Reassembly & Verification 10. Performance Testing 11. Technical Support & Warranty

Safety Precautions & Warnings

Before attempting any repair, disconnect the appliance from all power sources (AC mains and battery if applicable). Allow sufficient time for capacitors to discharge. Use appropriate personal protective equipment (PPE).

Hazard	Precaution
Electrical Shock	Always unplug the unit. Verify no voltage with a multimeter before touching internal components.
Sharp Edges	Wear cut-resistant gloves when handling internal chassis or sheet metal parts.
High Temperature	Allow the unit to cool completely if it has been in operation. Certain components may retain heat.
Chemical Exposure	Handle cleaning solvents and thermal compounds in a well-ventilated area.
Static Discharge	Use an anti-static wrist strap when handling circuit boards and sensitive electronics.

Model Identification & Specifications

Verify the model number (LMX25981ST) and serial number on the identification plate before ordering parts.

Model: LMX25981ST
Power Requirements: 120V AC, 60Hz, 15A.
Dimensions (HxWxD): Refer to unit-specific diagram.
Weight: Approximately [Weight] lbs/kg.
Key Subsystems: Main Control Board, Power Supply Unit, Display Interface, Motor Assembly, Sensor Array.
Operating Environment: Indoor use only. Temperature range: 50°F to 104°F (10°C to 40°C).

Tools & Test Equipment Required

Gather all necessary tools before beginning repair to ensure efficiency and safety.

Multimeter: For measuring voltage, resistance, and continuity.
Torx & Phillips Screwdrivers: Set of various sizes.
Hex Key Set: Metric and SAE.
Nut Drivers: For fastener removal.
Plastic Spudgers/Pry Tools: To avoid damaging plastic housings.
Anti-Static Mat & Wrist Strap: For ESD protection.
Soldering Iron & Desoldering Tool: For board-level repairs.

WARNING! Using incorrect tools can damage components and void the warranty.

Component Location & Diagrams

Refer to the exploded-view diagrams for precise location of all major assemblies, fasteners, and connectors.

Main Assembly: Shows the relationship between the outer casing, internal frame, and primary components.

Control Panel: Details the button membrane, display module, and connecting ribbon cables.

Power Supply Board: Identifies fuses, transformers, rectifiers, and output connectors.

Main Logic Board: Highlights the microprocessor, memory, communication chips, and input/output headers.

Mechanical Drive: Illustrates motor, gears, belts, and any moving parts.

Diagnostic Flowcharts & Error Codes

Use the following process to diagnose common failures. Error codes (if displayed) provide the first clue.

Observe the symptom and note any error codes on the display.
Consult the error code table (e.g., E1: Motor Fault, E2: Sensor Error, E3: Over-temperature).
Follow the corresponding diagnostic flowchart to isolate the faulty subsystem (Power, Control, Mechanical).
Perform voltage checks at test points indicated on the board schematics.
Check sensor resistances and actuator continuity against specified values.

Tip: Clear error codes after repair by cycling power or using the service menu reset function.

Disassembly Procedure

Disassemble in the exact order specified to avoid damage. Document or photograph cable orientations.

Power down and unplug the unit. Remove any external covers or panels.
Remove rear service panel screws (typically Torx T10/T15).
Carefully detach the main housing by releasing plastic clips with a spudger.
Disconnect all wire harnesses and ribbon cables from the main board, noting their positions.
Remove the screws securing the main board and power supply to the chassis.
Lift out assemblies as needed for access to underlying mechanical parts.

WARNING! Ribbon cables are fragile. Use the locking tab to release, do not pull on the cable.

Troubleshooting Common Faults

Symptom	Possible Cause	Corrective Action
Unit does not power on	Blown fuse, faulty power switch, dead power supply.	Check mains fuse. Test AC voltage at power board input. Check DC outputs (e.g., 5V, 12V).
Display is blank/unresponsive	Failed display, loose ribbon cable, faulty main board.	Reseat display cables. Test voltage to display backlight. Swap display module if possible.
Unusual noise during operation	Worn bearing, foreign object, unbalanced motor.	Inspect fan and motor assemblies. Remove debris. Lubricate per manual (if specified).
Error code persists after reset	Failed sensor, shorted wiring, damaged control IC.	Test sensor output. Check for continuity/shorts in sensor wiring. Replace sensor or main board.
Intermittent operation	Loose connection, cracked solder joint, overheating.	Reseat all connectors. Visually inspect board for bad solder. Ensure cooling vents are clear.

Parts List & Replacement

Use only genuine LG replacement parts (part numbers listed) to ensure compatibility and safety.

Main Control Board: Part # AAX1234567
Power Supply Assembly: Part # BBX7654321
Display Module: Part # CCX9876543
Main Drive Motor: Part # DDX1122334
Thermal Sensor: Part # EEX4455667
External Housing: Part # FFX7788990
Fastener Kit: Part # GGX0011223 (includes all screws/clips)

CAUTION! Installing non-OEM parts may cause malfunction and void the product warranty.

Reassembly & Verification

Reverse the disassembly steps precisely. Ensure all cables are routed correctly to avoid pinching.

Reinstall mechanical assemblies and secure with the correct fasteners.
Reconnect all wiring harnesses and ribbon cables, ensuring they are fully seated and locked.
Replace the main board and power supply, securing all mounting screws.
Reattach the main housing, engaging all plastic clips before tightening screws.
Install the rear service panel.
Before applying power, perform a visual inspection to ensure no tools or parts are left inside.

Performance Testing

After reassembly, conduct a full functional test to verify the repair.

Plug the unit into a properly grounded outlet.
Power on and observe the startup sequence. Listen for abnormal noises.
Navigate through all primary functions using the control panel.
Verify that error codes no longer appear.
Run a diagnostic cycle from the service menu (if available) to confirm all subsystems pass.
Let the unit run under load for a minimum of 15 minutes to check for intermittent faults.

Tip: Document test results and any replaced parts for service records.

Technical Support & Warranty

This manual is for certified technicians. Unauthorized modifications may violate safety standards and void warranties.

LG Service Network: For complex issues or board-level schematics, contact authorized LG service centers.

Warranty Note: Repairs using this manual do not extend the original product warranty. Parts replaced under warranty must be processed through an authorized channel.

Support Contact: LG Electronics Service Division: 1-800-243-0000. Website: www.lg.com/us/support.