McIntosh MX120 Audio/Video Processor Repair Guide

Model Overview

The McIntosh MX120 is a high-end audio/video processor introduced in the early 2000s. It represents McIntosh's approach to home theater processing with premium components and build quality. The MX120 features advanced surround sound processing, video switching, and room correction capabilities. It maintains the classic McIntosh appearance with blue backlit display, glass front panel, and professional connectivity options.

Common Issues and Solutions

Power Supply Problems

The MX120 power supply can develop specific issues:

• Capacitor failure: Electrolytic capacitors dry out, causing various power issues
• Rectifier issues: Rectifiers can fail under load
• Voltage regulator failure: Regulator ICs can fail, causing incorrect voltages
• Heat-related issues: The power supply runs warm and can suffer from thermal stress
• Standby circuit problems: Issues with the standby power circuit

Audio Section Problems

Common audio processing issues include:

• Digital processor lockups: DSP chips may require resetting
• DAC issues: Digital-to-analog converters can develop problems
• Input/output problems: Connection issues with audio inputs/outputs
• No audio output: Complete loss of audio signal
• Intermittent audio: Audio cutting in and out
• Balance issues: Channel imbalance or complete loss of one channel

Video Section Problems

The video processing section can develop issues:

• Video switching problems: Issues with input/output selection
• No video output: Complete loss of video signal
• Poor video quality: Degraded video performance
• Component video issues: Problems with YPbPr connections
• OSD problems: On-screen display malfunctions

Control & Interface Problems

Common control issues include:

• Front panel display issues: Problems with the main display
• Button/encoder problems: Issues with front panel controls
• Remote control issues: Problems with IR reception
• Software glitches: Firmware or software-related problems
• Memory loss: Settings not being retained
• Communication errors: Problems with internal data buses

Capacitor Replacement Guide

The following capacitors should be replaced in any comprehensive restoration:

Critical Components to Check/Replace

Component	Reference	Location	Notes
Voltage Regulators	IC101, IC102, IC103	Power Supply	Check for proper output voltages (+5V, ±12V, +3.3V)
Digital Processors	IC201 (DSP), IC202	Main Board	Check for proper operation and reset if needed
Memory ICs	IC301, IC302	Digital Board	Check for data corruption issues
Audio DACs	IC401, IC402	Audio Board	Check for proper audio conversion
Video Processors	IC501	Video Board	Check for video switching issues
Display Driver	IC601	Front Panel	Check for display issues
Microcontroller	IC701	Control Board	Main system controller, check for communication issues

Restoration Procedure

1. Disconnect power and remove covers
2. Discharge all capacitors completely
3. Document all connections with photos before disassembly
4. Replace all electrolytic capacitors, focusing on power supply first
5. Check and replace out-of-spec resistors
6. Clean all controls and switches with contact cleaner
7. Check voltage regulators and replace if necessary
8. Reseat all socketed ICs and connectors
9. Clean all board connectors and edge connectors
10. Inspect for cold solder joints, especially on larger components
11. Reassemble and power up slowly using a variac
12. Check all voltage rails according to service manual
13. Perform factory reset if necessary
14. Verify proper operation of all functions

Calibration Procedure

After restoration, these calibrations are essential:

• Check all voltage rails for proper values
• Verify proper operation of digital processors
• Test all audio inputs and outputs for each surround mode
• Test all video inputs and outputs at different resolutions
• Verify proper operation of surround sound processing
• Check display and front panel controls
• Test remote control functionality
• Verify proper operation of room correction features
• Check memory retention after power cycle
• Test trigger outputs and other control functions

Additional Tips

• Use high-quality, low-ESR capacitors for best performance
• Document all adjustments before making changes
• Check all connectors for corrosion or poor connections
• Clean all controls thoroughly as they often cause problems
• Allow the unit to warm up for 30 minutes before making final adjustments
• Consider replacing voltage regulators with modern equivalents
• Check for firmware updates if possible
• Inspect all PC boards for cracked traces or solder joints
• Pay special attention to the digital display circuitry
• Consider adding additional cooling if the unit runs hot
• Check the internal lithium battery for the memory backup circuit
• Use dielectric grease on connectors to prevent future corrosion