Marantz 170DC Service Manual

The Marantz 170DC is a high-quality stereo DC power amplifier featuring advanced DC circuitry, dual power meters, balanced inputs, and professional-grade construction. This service manual provides comprehensive technical information for qualified service technicians, including schematics, alignment procedures, troubleshooting guides, and replacement parts lists. Below are key sections for specifications, block diagrams, circuit descriptions, adjustment procedures, and maintenance guidelines.

1. Technical Specifications 2. Block Diagrams 3. Circuit Description 4. Adjustment Procedures 5. Disassembly Instructions 6. Parts List 7. Schematic Diagrams 8. Troubleshooting Guide 9. Maintenance & Service 10. Safety Precautions

Technical Specifications

Complete electrical and mechanical specifications for the Marantz 170DC stereo power amplifier.

Parameter	Specification
Power Output	85 watts per channel (8 ohms, 20Hz-20kHz)
Total Harmonic Distortion	0.03% at rated output
Frequency Response	5Hz - 50kHz (+0, -1dB)
Input Sensitivity	1.2V for rated output
Input Impedance	50k ohms
Damping Factor	60 at 8 ohms
Signal-to-Noise Ratio	110dB (IHF A-weighted)
Power Requirements	120V AC, 60Hz, 450W max
Dimensions	17-1/4" W × 5-3/4" H × 13-1/2" D
Weight	35 lbs (15.9 kg)

Block Diagrams

System block diagrams showing signal flow and power distribution.

Main Amplifier Block Diagram: Input stage, DC amplifier, output stage, protection circuits.
Power Supply Block Diagram: Transformer, rectifier, filter capacitors, regulation.
Protection Circuit Block Diagram: Overload detection, thermal protection, speaker relay.
Meter Circuit Block Diagram: Power meter drivers and calibration circuits.

WARNING! High voltage present in power supply section. Disconnect power before servicing.

Circuit Description

Detailed explanation of each circuit section and component function.

Input Stage: Balanced/unbalanced input circuitry with impedance matching.
DC Amplifier Circuit: Direct-coupled differential amplifier design.
Output Stage: Complementary symmetry output transistors with thermal tracking.
Protection Circuits: Overcurrent, overvoltage, and thermal protection systems.
Power Supply: Dual secondary transformer with bridge rectification.
Meter Circuitry: Peak-reading power meters with adjustable sensitivity.

CAUTION! Use proper grounding techniques when testing live circuits.

Adjustment Procedures

DC Offset Adjustment: Adjust VR101/VR102 for 0mV ±5mV output.
Bias Current Adjustment: Set VR103/VR104 for 20mA idle current.
Meter Calibration: Adjust meter sensitivity for accurate power readings.
Protection Circuit Test: Verify proper operation of overload protection.
Power Supply Voltages: Check ± supply rails for proper voltage levels.
Frequency Response: Verify flat response across audio spectrum.
Distortion Measurement: Confirm THD meets specifications.

Disassembly Instructions

Step-by-step guide for accessing internal components.

Procedure: Remove top cover screws, lift cover carefully. Remove front panel knobs and screws. Detach rear panel connectors. Remove bottom plate for circuit board access.

Front Panel: Power switch, input selectors, meter assembly, balance control.

Rear Panel: Speaker terminals, input connectors, AC power cord, fuse holder.

Parts List

Complete list of components with manufacturer part numbers.

Reference	Description	Part Number
Q101-Q104	Input differential transistors	2SC1571
Q105-Q108	Driver transistors	2SC2238/2SA968
Q109-Q112	Output transistors	2SC2581/2SA1106
D101-D104	Protection diodes	1S2473
TR101	Power transformer	TPC-301
C101-C104	Power supply capacitors	10,000μF/63V
F101	Main fuse	5A slow-blow

Schematic Diagrams

Complete schematic diagrams for all circuit sections.

Main Amplifier Schematic: Left and right channel amplifier circuits.
Power Supply Schematic: Transformer, rectifiers, filter network.
Protection Circuit Schematic: Relay drivers and detection circuits.
Meter Circuit Schematic: Peak detection and meter movement circuits.
Control Circuit Schematic: Input switching and balance controls.

Tip: Use high-quality prints for accurate component identification.

Troubleshooting Guide

Systematic approach to diagnosing and repairing common issues.

Symptom	Possible Cause	Corrective Action
No output	Blown fuse, protection circuit	Check F101, test protection relay, measure output transistors
Distorted sound	Bias current, DC offset	Adjust bias and offset, check driver transistors
Intermittent operation	Cold solder joints, connectors	Resolder main board, clean input/output connectors
Meter not working	Meter circuit, diodes	Check meter movement, test D101-D104
Hum/buzz	Ground loops, filter caps	Replace C101-C104, check grounding

Maintenance & Service

Routine maintenance procedures and service intervals.

Clean controls and connectors annually. Check bias current every 2 years. Replace electrolytic capacitors after 10 years. Clean ventilation openings regularly.

CAUTION! Always discharge power supply capacitors before servicing.

Safety Precautions

Essential safety information for service technicians.

Use isolation transformer when testing live circuits. Wear safety glasses. Follow proper ESD precautions. Verify proper grounding. Use correct fuse ratings. Keep work area clean and organized.