McIntosh MAC 1700 Receiver Repair Guide

Model Overview

The McIntosh MAC 1700 is a solid-state receiver introduced in 1967 as an upgrade to the MAC 1500. It features a completely solid-state design with 55 watts per channel output power. The MAC 1700 retains the classic McIntosh appearance with blue meters, glass front panel, and walnut cabinet. It features McIntosh's patented Unity Coupled output circuit and Sentry Monitoring protection.

Common Issues and Solutions

Power Supply Problems

The MAC 1700 power supply can develop specific issues:

• Capacitor failure: Electrolytic capacitors dry out, causing hum and power issues
• Rectifier issues: Silicon rectifiers can fail over time
• Resistor drift: Carbon composition resistors can drift out of specification
• Voltage regulator failure: Transistor-based regulators can fail

Amplifier Section Problems

Common amplifier issues include:

• Output transistor failure: The silicon output transistors can fail
• Driver transistor issues: Driver transistors can become leaky
• DC offset: Improper DC offset can damage speakers
• Bias drift: Bias current can drift over time
• Potentiometer noise: Dirty controls cause crackling in audio

Tuner Section Problems

The solid-state tuner section can develop issues:

• Alignment issues: FM/AM alignment can drift over time
• Transistor failure: RF and IF transistors can become noisy
• Capacitor failure: Small-value capacitors can drift
• Switch contacts: Dirty selector switches cause signal loss

Capacitor Replacement Guide

The following capacitors should be replaced in any comprehensive restoration:

Critical Components to Check/Replace

Component	Reference	Location	Notes
Output Transistors	Q9, Q10, Q11, Q12	Amplifier Board	Check for failure and thermal paste condition
Driver Transistors	Q7, Q8	Amplifier Board	Check for proper operation
Rectifiers	SR1, SR2	Power Supply	Silicon rectifiers - check for failure
Voltage Regulators	Q1, Q2	Power Supply	Check for proper regulation
Filter Resistors	R1, R2	Power Supply	Check for value drift and overheating
Tuner Transistors	Q301-Q310	Tuner Board	Check for noise and proper operation

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
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. Reapply thermal compound to output transistors
10. Reassemble and power up slowly using a variac
11. Adjust bias and DC offset according to service manual
12. Perform alignment of tuner section if necessary

Calibration Procedure

After restoration, these calibrations are essential:

• Set DC offset to zero (adjust R33, R34)
• Adjust bias current (adjust R35, R36)
• Verify proper operation of Sentry Monitoring circuit
• If necessary, perform FM alignment using proper equipment
• Check and adjust AM alignment if needed
• Verify proper operation of all inputs and controls
• Check meter calibration

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
• Consider replacing the silicon rectifiers with modern equivalents
• Pay special attention to the thermal compound on output transistors
• Check the protection circuit (Sentry Monitoring) for proper operation
• Inspect all PC boards for cracked traces or solder joints
• Clean the meter movements carefully if they're sticking