McIntosh MX117 Stereo Tuner/Preamplifier Repair Guide

IMPORTANT DISCLAIMER: This article is provided for informational purposes only. I am not responsible for the accuracy of this information. The content may or may not be accurate, and any repairs attempted based on this information are done at your own risk. Always consult a qualified technician for electronic repairs, especially with high-end equipment like the McIntosh MX117.

SAFETY WARNING: Always disconnect the unit from power before working internally. This unit contains high voltages that can be lethal. Discharge large capacitors before handling. Exercise extreme caution when working on tube-based sections if applicable.

CRITICAL NOTE: The McIntosh MX117 is a sophisticated stereo tuner/preamplifier that may contain both solid-state and tube circuitry depending on the version. Exercise extreme caution around the power supply sections. Always use a variac for initial power-up after repairs.

Model Overview

The McIntosh MX117 is a premium stereo tuner/preamplifier that combines high-quality FM/AM tuning capabilities with sophisticated preamplifier functions. This component features McIntosh's renowned build quality and attention to detail, offering exceptional audio performance for both tuner and line-level sources. The MX117 maintains the classic McIntosh appearance with blue backlit meters, glass front panel, and professional-grade construction typical of McIntosh components from this era.

Tuner Section

FM/AM with multiplex stereo

Frequency Response

20Hz - 20kHz (±0.5dB)

Total Harmonic Distortion

0.1% (FM), 0.5% (AM)

Inputs

Multiple high-level inputs, phono MM/MC

Outputs

Main outputs, tape outputs

Technology

Solid-state (some versions may have tubes)

Common Issues and Solutions

Power Supply Problems

The MX117 power supply can develop specific issues:

Capacitor failure: Electrolytic capacitors can dry out over time
Rectifier issues: Rectifiers can fail, causing power supply problems
Voltage regulator failure: Regulator circuits can develop issues
Transformer hum: Power transformer may develop mechanical hum
Heater supply issues: Tube heater supply problems (tube versions)

Tuner Section Problems

The sophisticated tuner section can develop issues:

Alignment issues: FM/AM alignment can drift over time
Oscillator drift: Local oscillator frequency may drift
Multiplex issues: Stereo decoder problems
Signal strength meter issues: Tuner meter calibration problems
Selector switch issues: Band selection problems
Noisy operation: Transistor or tube noise in RF stages

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
Tube microphonics: Tube sensitivity to vibration (tube versions)

Control & Display Issues

Control and display systems can malfunction:

Meter movement problems: Signal strength and tuning meters
Dial lamp issues: Backlighting and indicator lamp failures
Switch contact problems: Dirty or worn switch contacts
Control logic issues: Problems with electronic switching

Capacitor Replacement Guide

The following capacitors should be replaced in any comprehensive restoration:

Power Supply Section

C101, C102: 2200μF 35V - Main filter capacitors

C103, C104: 1000μF 25V - Secondary filter capacitors

C105, C106: 470μF 25V - Regulation capacitors

C107, C108: 220μF 16V - Bypass capacitors

C109, C110: 100μF 16V - Tube heater supply (if applicable)

Tuner RF/IF Section

C201-C210: Various values - Tuning and alignment capacitors

C211-C215: 4.7μF 50V - Coupling capacitors

C216-C220: 22μF 25V - Bypass capacitors

C221-C225: 0.47μF 100V - Decoupling capacitors

Preamplifier Section

C301-C308: 10μF 25V - Input coupling capacitors

C309-C316: 47μF 16V - EQ circuit capacitors

C317-C324: 100μF 16V - Output coupling capacitors

C325-C328: 0.47μF 100V - Tone control capacitors

Phono Stage

C401, C402: 1μF 50V - Input coupling capacitors

C403, C404: 0.1μF 100V - RIAA equalization capacitors

C405, C406: 47μF 16V - Power supply decoupling

C407, C408: 10μF 25V - Output coupling capacitors

Critical Components to Check/Replace

Component	Reference	Location	Notes
Tuner RF Transistors/Tubes	Q201-Q204 or V1-V4	Tuner Board	Check for noise and proper operation
IF Amplifiers	Q205-Q208 or V5-V8	Tuner Board	Critical for signal amplification
Multiplex Decoder	IC301 or discrete components	Tuner Board	Check for proper stereo separation
Phono Stage Transistors/Tubes	Q401-Q404 or V9-V12	Phono Board	Check for low-noise operation
Voltage Regulators	IC101, IC102	Power Supply	Check for proper output voltages
Selector Switches	S101-S104	Front Panel	Clean or replace if noisy
Potentiometers	VR101-VR104	Front Panel	Clean or replace if scratchy

Note: The MX117 uses high-quality components throughout. When replacing parts, use equivalent or better quality components. Pay special attention to the tuner alignment procedures which require specialized equipment. Tube versions require careful bias adjustments.

Restoration Procedure

Disconnect power and remove covers
Discharge all capacitors completely
Document all wiring with photos before disassembly
Replace all electrolytic capacitors, starting with power supply
Check and replace out-of-spec resistors
Clean all controls and switches with contact cleaner
Check transistors/tubes and replace if necessary
Clean all switch contacts and potentiometers
Check and clean tube sockets (if applicable)
Reassemble and power up slowly using a variac
Check all voltage rails according to service manual
Perform tuner alignment if necessary
Verify proper operation of all functions

Calibration Procedure

After restoration, these calibrations are essential:

Check all voltage rails for proper values
Perform FM/AM alignment using proper equipment
Adjust stereo decoder for proper separation
Check phono stage gain and RIAA equalization
Verify proper operation of all inputs and controls
Check meter calibration for signal strength and tuning
Adjust tube biases if applicable
Test all switching functions

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
For tube versions, use matched tube sets for best performance
Inspect all PC boards for cracked traces or solder joints
Consider replacing dial lamps with LED equivalents for longer life
Keep service manual handy for specific adjustment procedures

DISCLAIMER REPEATED FOR EMPHASIS: This information is provided as-is without warranty of any kind. I am not responsible for the accuracy of this information or any damage that may occur from its use. Always consult a qualified technician for repairs on high-end audio equipment.