Marantz PM 730 Service Manual

The Marantz PM 730 is a high-quality stereo integrated amplifier featuring dual mono construction, gold-plated connectors, phono input for turntables, tape monitoring circuits, loudness control, and high-current power supply. With 70 watts per channel into 8 ohms, this amplifier delivers exceptional audio performance for audiophile applications. Below are key sections for technical specifications, circuit descriptions, adjustment procedures, troubleshooting, and service data.

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

Technical Specifications

Complete technical specifications for the Marantz PM 730 integrated amplifier.

Parameter	Specification
Power Output	70W + 70W (8Ω, 20Hz-20kHz, 0.02% THD)
Total Harmonic Distortion	0.02% (20Hz-20kHz at rated output)
Frequency Response	5Hz-50kHz (+0/-3dB)
Input Sensitivity	Phono: 2.5mV, Line: 150mV
Signal-to-Noise Ratio	Phono: 80dB, Line: 100dB
Damping Factor	100 (8Ω, 1kHz)
Tone Control	Bass: ±10dB at 100Hz, Treble: ±10dB at 10kHz
Power Supply	AC 120V/230V, 50/60Hz, 280W max consumption
Dimensions	440 x 130 x 360mm (W x H x D)
Weight	10.5 kg

Block Diagram & Circuit Description

Detailed circuit analysis and block diagram explanation.

Power Supply Section: Dual mono design with separate transformer windings for left/right channels
Pre-amplifier Stage: Phono equalizer using low-noise transistors, line amplifier with flat frequency response
Power Amplifier Section: Complementary symmetry output stage with triple Darlington configuration
Protection Circuit: DC detection, over-current protection, thermal shutdown
Control Circuits: Volume, balance, tone controls, input selector, tape monitor

IMPORTANT! Always disconnect power before performing any circuit measurements.

Disassembly Instructions

Step-by-step disassembly procedure for service access.

Remove top cover: Unscrew 6 Phillips screws from top panel
Remove bottom cover: Turn unit upside down, remove 8 screws
Front panel removal: Remove knobs, unscrew 4 front panel screws
PCB access: Remove relevant screws and carefully lift boards
Heat sink removal: Required for output transistor replacement

CAUTION! Handle PCBs carefully to avoid damaging traces and components.

Adjustment Procedures

Factory adjustment and calibration procedures.

DC Offset Adjustment: Adjust VR701/VR702 for 0mV ±5mV at speaker terminals
Bias Current Adjustment: Set VR703/VR704 for 15mA across emitter resistors
Phono Equalization: Verify RIAA curve compliance using test equipment
Protection Circuit Test: Verify proper operation of DC protection and relay timing

WARNING! Use isolation transformer when making live adjustments.

Schematic Diagrams

Complete schematic diagrams for all circuit sections.

Main Amplifier Circuit: Power amplifier and driver stages
Power Supply: Transformer, rectification, and filtering
Pre-amplifier Section: Phono EQ, line stage, tone controls
Protection Circuit: Speaker protection and thermal management
Control Logic: Input selection, muting circuits

Parts List & PCB Layout

Complete component listing and board layout information.

Reference	Description	Part Number
Q701-Q704	Output Transistor 2SC2581/2SA1106	Marantz 2581-1106
IC701, IC702	Driver IC NJM2068	Marantz 2068-001
TR001	Power Transformer	Marantz TRA-730
C701-C704	Main Filter Capacitor 10000μF/63V	Marantz CAP-10000-63
F701, F702	Main Fuse 4A slow-blow	Marantz FUSE-4ASB

Troubleshooting Guide

Common problems and solutions for the PM 730.

Symptom	Possible Cause	Corrective Action
No power	Fuse blown, power switch	Check F701/F702; test power switch; verify transformer output
Distorted audio	Bias current, output transistors	Adjust bias current; test output transistors Q701-Q704
DC offset high	Input differential pair	Check Q101/Q102; adjust VR701/VR702
Protection relay not engaging	Protection circuit fault	Test Q751-Q754; check relay driver circuit
Hum in output	Grounding, filter capacitors	Verify ground connections; test C701-C704

Service Notes

Important service information and common repair procedures.

Always replace output transistors in complementary pairs
Use thermal compound when reinstalling heat sinks
Verify bias current stabilizes after 30 minutes of operation
Check all solder joints on power supply and output sections
Use original Marantz parts for critical components

NOTE: Document all adjustments made during service.

Safety Precautions

Essential safety procedures for service technicians.

WARNING! High voltages present - discharge power supply capacitors before working. Use proper grounding techniques. Follow ESD precautions when handling semiconductors.

Warranty Information

Marantz warranty terms and service center information.

This service manual is intended for qualified service technicians only. Marantz provides a 2-year limited warranty on parts and labor. For authorized service, contact Marantz Service Department at 1-800-4-MARANTZ or visit www.marantz.com. Serial number location: Rear panel near power cord entry.