Luxman L505UXII Integrated Amplifier Services

Model Overview

The Luxman L505UXII is a premium integrated amplifier featuring Luxman's proprietary ODNF (Only Distortion Negative Feedback) Version 4.0 amplification technology. This balanced design amplifier delivers 100 watts per channel into 8 ohms with exceptional clarity and musicality. The L505UXII represents the perfect balance of power, refinement, and Luxman's legendary build quality, featuring high-quality components throughout and the classic Luxman aesthetic.

Common Issues and Solutions

Power Supply Problems

The L505UXII power supply can develop specific issues:

• Capacitor failure: Large electrolytic capacitors can dry out over time
• Rectifier issues: High-current rectifiers can fail under load
• Transformer hum: Power transformer may develop mechanical hum
• Voltage regulator failure: Regulator circuits can develop problems
• Soft-start circuit issues: Problems with the protection circuitry

ODNF Amplifier Section Problems

Specific to ODNF amplification technology:

• Output transistor failure: Power output transistors can fail
• Bias drift: Bias current can drift over time, affecting performance
• DC offset: Improper DC offset can damage speakers
• ODNF circuit issues: Problems with the distortion cancellation circuitry
• Protection circuit activation: Unit may stay in protection mode

Preamplifier Section Problems

The preamplifier section can develop issues:

• Potentiometer noise: Dirty volume/control pots cause crackling
• Selector switch issues: Input selection problems
• Phono stage problems: Issues with the MM/MC phono input
• Balance control problems: Channel balance issues
• Tone control issues: Problems with bass/treble controls

Protection Circuit Issues

The protection system can malfunction:

• Relay failure: Speaker protection relay may not engage
• False protection triggering: Unit enters protection mode unnecessarily
• Delay circuit problems: Speaker delay not functioning properly
• DC detection issues: DC offset detection circuit malfunctions

Capacitor Replacement Guide

The following capacitors should be replaced in any comprehensive restoration:

Critical Components to Check/Replace

Component	Reference	Location	Notes
Output Transistors	Q101-Q104	Amplifier Board	Check for failure and thermal paste condition
Driver Transistors	Q201-Q204	Amplifier Board	Check for proper operation
ODNF Circuit Transistors	Q301-Q304	Amplifier Board	Critical for distortion cancellation
Voltage Regulators	IC101, IC102	Power Supply	Check for proper output voltages
Protection Relay	RLY101	Protection Board	Check for contact oxidation
Power Resistors	R101-R104	Power Supply	Check for value drift and overheating
Bias Transistors	Q401, Q402	Amplifier Board	Critical for proper bias setting

Restoration Procedure

1. Disconnect power and remove covers
2. Discharge all capacitors completely
3. Document all wiring with photos before disassembly
4. Replace all electrolytic capacitors, starting with power supply
5. Check and replace out-of-spec resistors
6. Clean all controls and switches with contact cleaner
7. Check output transistors and replace if necessary
8. Check driver transistors and replace if necessary
9. Clean protection relay contacts
10. Reapply thermal compound to output transistors
11. Reassemble and power up slowly using a variac
12. Adjust bias and DC offset according to service manual
13. Verify proper operation of protection circuit

Calibration Procedure

After restoration, these calibrations are essential:

• Set DC offset to zero (adjust VR101, VR102)
• Adjust bias current (adjust VR103, VR104)
• Verify proper operation of ODNF circuitry
• Check phono stage gain and RIAA equalization
• Verify proper operation of all inputs and controls
• Check balance and tone controls
• Test headphone output
• Verify proper operation of protection circuits

Additional Tips

• Use high-quality, audio-grade capacitors for best performance
• Document all adjustments before making changes
• Check all resistors near replaced components; they may have drifted in value
• Clean all controls thoroughly as they often cause noise
• Allow the unit to warm up for 30 minutes before making final adjustments
• Use Deoxit or similar contact cleaner on all switches and potentiometers
• Check the thermal compound on heat sinks and reapply if necessary
• Inspect all PC boards for cracked traces or solder joints
• Consider upgrading binding posts and RCA connectors if worn
• Verify ODNF circuit operation by checking distortion characteristics