Marantz 15 Service Manual

The Marantz 15 is a classic stereo amplifier known for its exceptional audio quality and robust construction. This service manual provides comprehensive technical documentation for servicing, troubleshooting, and maintaining the Marantz 15 amplifier. Below are key sections covering specifications, circuit diagrams, alignment procedures, component lists, and repair guidelines.

1. Technical Specifications 2. Circuit Description 3. Block Diagrams 4. Alignment Procedures 5. Parts List 6. Schematic Diagrams 7. Mechanical Assembly 8. Troubleshooting Guide 9. Service Notes 10. Safety Precautions 11. Warranty Information

Technical Specifications

Complete technical specifications for the Marantz 15 stereo amplifier.

ParameterSpecification
Power Output30 Watts per channel (RMS)
Frequency Response20Hz - 20kHz ±0.5dB
Total Harmonic Distortion<0.1% at rated output
Input Sensitivity2.5mV (MM), 150mV (Line)
Signal-to-Noise Ratio75dB (MM), 90dB (Line)
Input Impedance47kΩ (Phono), 100kΩ (Line)
Damping Factor>50 at 8Ω
Power Requirements120V AC, 60Hz, 200W
Dimensions17" W × 5" H × 13" D
Weight25 lbs

Circuit Description

Detailed description of the amplifier's circuit topology and design principles.

  1. Power Supply: Dual-rail design with regulated supplies for critical stages
  2. Preamplifier: Discrete transistor phono stage with RIAA equalization
  3. Tone Control: Baxandall-type bass and treble controls
  4. Power Amplifier: Complementary symmetry output stage with thermal protection
  5. Protection Circuits: DC offset protection and thermal shutdown

IMPORTANT! Always discharge power supply capacitors before servicing.

Block Diagrams

System block diagrams showing signal flow and interconnections.

Alignment Procedures

Step-by-step alignment and calibration procedures.

  1. DC Offset Adjustment: Adjust VR101 for 0V DC at speaker terminals
  2. Bias Current Adjustment: Set VR102 for 25mA quiescent current
  3. Phono Equalization: Verify RIAA response using test equipment
  4. Level Matching: Balance channel outputs using test tones

CAUTION! Use insulated tools and follow electrostatic discharge precautions.

Parts List

Complete component listing with manufacturer part numbers.

ReferenceDescriptionPart Number
Q101-Q104Output Transistors2SC2565/2SA1095
C201-C204Main Filter Capacitors6800μF/63V
R101-R110Metal Film ResistorsVarious values
VR101, VR102Multi-turn Trimmers500Ω, 2kΩ
F101, F102Slow-blow Fuses3A, 250V

Schematic Diagrams

Detailed schematic diagrams for all circuit sections.

  1. Main Amplifier Schematic: Complete audio amplification circuit
  2. Power Supply Schematic: Transformer, rectification, and regulation
  3. Control Board Schematic: Protection and switching circuits
  4. Front Panel Schematic: Input selection and tone controls

Note: All schematics include component values and test points.

Mechanical Assembly

Mechanical drawings and assembly instructions.

Troubleshooting Guide

Systematic troubleshooting procedures for common issues.

SymptomPossible CauseCorrective Action
No outputBlown fuses, faulty power supplyCheck F101, F102; measure supply voltages
Distorted audioBias misadjustment, faulty transistorsAdjust bias current; test output devices
Hum/buzzGround loops, filter capacitorsCheck grounding; replace C201-C204
Intermittent operationCold solder joints, loose connectorsInspect solder joints; reseat connectors
OverheatingExcessive bias, poor ventilationAdjust bias; ensure proper airflow

Service Notes

Important service tips and modification information.

Recommended test equipment: Oscilloscope, audio generator, distortion analyzer, multimeter. Common upgrades: Higher quality capacitors, upgraded op-amps (where applicable), improved heat sinking.

WARNING! Always use original or approved replacement parts.

Safety Precautions

Essential safety procedures for service technicians.

  1. Always disconnect from AC power before servicing
  2. Use isolation transformer when working on live circuits
  3. Discharge large capacitors before handling
  4. Follow electrostatic discharge precautions
  5. Verify proper grounding after repairs

DANGER! Lethal voltages present - exercise extreme caution.

Warranty Information

Warranty terms and service center information.

Original warranty: 2 years parts and labor. Service centers: Authorized Marantz service centers worldwide. For service assistance, contact Marantz technical support at 1-800-MARANTZ or visit www.marantz.com.

Marantz 15 Service Manual © - All Rights Reserved 2025