Marantz PM 55 Service Manual

The Marantz PM 55 is a high-quality stereo integrated amplifier featuring advanced audio circuitry, multiple input/output options, and professional-grade components. This service manual provides comprehensive technical information for service technicians, including schematics, adjustment procedures, troubleshooting guides, and replacement part specifications. Below are key sections covering technical specifications, circuit descriptions, adjustment procedures, and maintenance guidelines.

1. Technical Specifications 2. Block Diagram Overview 3. Circuit Descriptions 4. Adjustment Procedures 5. Disassembly Instructions 6. Parts List & Replacement 7. Schematic Diagrams 8. PCB Layouts 9. Troubleshooting Guide 10. Safety Precautions 11. Service Notes

Technical Specifications

Complete technical specifications for the Marantz PM 55 integrated amplifier.

ParameterSpecification
Power Output80W + 80W (8Ω, 20Hz-20kHz, 0.08% THD)
Frequency Response5Hz - 100kHz (+0/-3dB)
Total Harmonic Distortion0.008% (1kHz, 50W, 8Ω)
Input SensitivityPhono: 2.5mV, CD: 150mV, Tuner: 150mV
Signal-to-Noise RatioPhono: 86dB, CD: 100dB
Input ImpedancePhono: 47kΩ, CD: 47kΩ
Tone ControlBass: ±10dB at 100Hz, Treble: ±10dB at 10kHz
Power SupplyAC 120V/230V, 50/60Hz
Dimensions440mm × 130mm × 350mm (W×H×D)
Weight8.5kg

Block Diagram Overview

System block diagram showing signal flow and major circuit blocks.

  1. Input Selector: Phono, CD, Tuner, Aux, Tape inputs
  2. Phono Equalizer: RIAA equalization circuit
  3. Tone Control: Bass and treble adjustment circuits
  4. Volume Control: ALPS motorized potentiometer
  5. Power Amplifier: Dual-monaural power amplifier stage
  6. Protection Circuit: DC detection and thermal protection
  7. Power Supply: Toroidal transformer with regulated supplies

WARNING! High voltages present in power supply section. Exercise extreme caution when servicing.

Circuit Descriptions

Detailed descriptions of major circuit sections and their operation.

  1. Input Stage: JFET input circuitry for low noise performance
  2. Phono Stage: Discrete transistor RIAA equalization amplifier
  3. Tone Control: Baxandall-type bass and treble controls
  4. Power Amplifier: Complementary symmetry output stage with current mirror
  5. Protection Circuit: Relay-based speaker protection with DC detection
  6. Power Supply: Dual secondary toroidal transformer with bridge rectifiers

CAUTION! Always discharge power supply capacitors before servicing.

Adjustment Procedures

Disassembly Instructions

Step-by-step disassembly procedure for service access.

Front Panel Removal: Remove volume knob, unscrew 4 front panel screws

  1. Remove top cover: 6 screws on rear and sides
  2. Remove bottom cover: 4 screws on bottom panel
  3. Front panel assembly: Disconnect ribbon cables carefully
  4. Main board access: Remove shield covers as needed
  5. Power supply board: Disconnect all wiring connectors

Tip: Document cable positions and take photos during disassembly.

Parts List & Replacement

Critical replacement parts and equivalents.

Part NumberDescriptionReplacement
2SC2240Input stage transistorKSC1845
2SA970Complementary input transistorKSA992
2SC2705Driver transistorMJE15032
2SA1145Complementary driverMJE15033
2SC3281Output transistorMJL3281A
2SA1302Complementary outputMJL1302A
10000μF/63VMain filter capacitorSame value, 35mm dia.
ALPS RK27Volume potentiometerALPS RK27112A

Schematic Diagrams

Complete schematic diagrams for all circuit sections.

  1. Main Amplifier Circuit: Left and right channel power amplifiers
  2. Pre-amplifier Section: Phono, tone control, and input switching
  3. Power Supply: Main power supply and regulated supplies
  4. Protection Circuit: Speaker protection and relay driver
  5. Control Circuit: Input selection and mode switching

WARNING! Schematics show lethal voltages. Service by qualified personnel only.

PCB Layouts

Printed circuit board layouts and component placement diagrams.

Main Board: Component side and solder side views with reference designators

  1. Power Supply Board: Component placement and trace routing
  2. Input/Selector Board: Switch and input connector locations
  3. Front Panel Board: Display and control button layout
  4. Grounding Scheme: Star grounding points and signal ground separation

CAUTION! Observe proper grounding when reassembling to prevent hum.

Troubleshooting Guide

Systematic troubleshooting procedures for common issues.

SymptomPossible CauseCorrective Action
No sound outputProtection relay, blown fusesCheck speaker relay, measure output DC offset, replace fuses
Distorted soundBias current, damaged outputsAdjust bias current, check output transistors, verify rail voltages
Hum in audioGround loops, filter capsCheck grounding, replace filter capacitors, verify shield connections
One channel deadOpen components, broken tracesCompare good channel measurements, check for open resistors/caps
OverheatingExcessive bias, shorted outputsMeasure bias current, check for shorted transistors, verify heatsink contact

Safety Precautions

Essential safety procedures for service technicians.

Always disconnect AC power before servicing. Use isolation transformer when working on live circuits. Discharge large capacitors before measurement. Use appropriate personal protective equipment. Follow electrostatic discharge precautions for CMOS devices.

CAUTION! Lethal voltages present. Service by qualified technicians only.

Service Notes

Important service notes and common repair issues.

Service Support: Contact authorized Marantz service centers for technical assistance and genuine replacement parts.

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