Marantz MA700 Service Manual

The Marantz MA700 is a high-performance monoblock power amplifier featuring advanced circuitry, premium components, and robust construction. This service manual provides comprehensive technical information including specifications, schematics, adjustment procedures, troubleshooting guidelines, and replacement parts for qualified service technicians. Below are key sections covering technical overview, specifications, block diagrams, adjustment procedures, and service information.

Technical Overview

The MA700 monoblock amplifier employs a fully balanced differential design with dual-mono construction for superior channel separation and noise performance. Key components include toroidal power transformer, high-current output stages, and advanced protection circuitry.

Component	Description
Power Transformer	Custom toroidal design with separate windings
Output Devices	Matched bipolar transistors in triple-darlington configuration
Power Supply	Dual-mono design with separate rectification and filtering
Input Stage	Fully balanced differential amplifier
Protection Circuitry	DC offset, over-current, and thermal protection
Heat Sink	Extruded aluminum with forced air cooling
Binding Posts	Gold-plated 5-way speaker terminals
Input Connectors	RCA and XLR balanced inputs
Power Switch	Soft-start circuit with relay
Status Indicators	Power, protection, and signal present LEDs

Specifications

• Power Output: 200 watts RMS into 8 ohms, 400 watts into 4 ohms
• Frequency Response: 10Hz - 100kHz (+0/-3dB)
• Total Harmonic Distortion: <0.05% at rated power
• Signal-to-Noise Ratio: >110dB (A-weighted)
• Input Sensitivity: 1.2V for rated output
• Input Impedance: 47k ohms (RCA), 20k ohms (XLR)
• Damping Factor: >200 at 8 ohms
• Power Requirements: 120V AC, 60Hz, 500W maximum
• Dimensions: 17" W × 6" H × 16" D
• Weight: 35 lbs

Block Diagrams

Complete system block diagrams showing signal flow, power supply distribution, and protection circuitry.

1. Main Amplifier Block Diagram: Input stage → Voltage amplifier → Driver stage → Output stage
2. Power Supply Block Diagram: AC input → Transformer → Rectification → Filtering → Regulation
3. Protection Circuit Block Diagram: DC detection → Over-current sensing → Thermal monitoring → Relay control
4. Control System Block Diagram: Microcontroller → Status indicators → Protection relays → Thermal management

WARNING! High voltages present - discharge power supply capacitors before servicing.

Circuit Description

Detailed analysis of each circuit section with component functions and signal paths.

Input Stage: Balanced differential amplifier using matched JFETs for low noise and high linearity.

Voltage Amplifier: High-speed voltage gain stage with local feedback for stability.

Output Stage: Triple-darlington configuration with multiple output devices for high current delivery.

Power Supply: Dual-mono design with separate transformer windings, bridge rectifiers, and reservoir capacitors.

Adjustment Procedures

Step-by-step calibration and adjustment instructions for proper amplifier performance.

1. DC Offset Adjustment: Adjust VR101 for 0mV ±5mV at output terminals
2. Bias Current Adjustment: Set VR102 for 25mA quiescent current across emitter resistors
3. Protection Threshold: Verify DC protection activates at ±2V DC offset
4. Thermal Calibration: Confirm thermal protection at 85°C heatsink temperature

CAUTION! Use calibrated test equipment and follow safety procedures.

Disassembly Instructions

Proper disassembly sequence to access internal components for service.

1. Remove top cover: 8 Phillips screws on rear and sides
2. Remove front panel: 4 screws behind front bezel
3. Access main board: Remove 6 board mounting screws
4. Remove heat sink: Detach output devices and thermal compound
5. Power supply access: Disconnect transformer leads and mounting hardware

Tip: Document wire positions and take photos during disassembly.

Parts List

Complete component listing with manufacturer part numbers and substitutions.

Reference	Description	Part Number	Substitution
Q101-Q104	Input JFET	2SK389BL	2SK170GR (matched)
Q201-Q208	Driver Transistor	2SC3421	MJE15032
Q301-Q308	Output Transistor	2SC5200	MJL21193
D101-D104	Rectifier Diode	UF4007	1N4007
C101-C104	Power Supply Cap	10000μF/63V	Same value
R201-R208	Emitter Resistor	0.22Ω/5W	Same value
VR101, VR102	Trimmer Pot	500Ω multi-turn	Same type

Schematic Diagrams

Complete schematic diagrams for all circuit boards including main amplifier, power supply, and protection circuits.

1. Main Amplifier Schematic: Full circuit diagram with component values
2. Power Supply Schematic: Transformer, rectification, and filtering circuits
3. Protection Circuit Schematic: DC offset, over-current, and thermal protection
4. Control Board Schematic: Microcontroller, status LEDs, and relay drivers

WARNING! Schematics show lethal voltages - exercise extreme caution.

PCB Layouts

Printed circuit board layouts showing component placement, trace routing, and test points.

• Main Amplifier Board: Top and bottom layer views with component designations
• Power Supply Board: High-current traces and component placement
• Control Board: Digital section layout and interface connections
• Front Panel Board: Switch and indicator circuit layout

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
No power	Fuse, power switch, transformer	Check main fuse F101; verify AC input; test transformer primary
Protection mode	DC offset, short circuit, thermal	Measure DC offset; check output devices; verify thermal sensor
Distorted output	Bias current, damaged devices	Adjust bias current; test output transistors; check driver stage
Hum/buzz	Ground loop, power supply	Check ground connections; test filter capacitors; verify rectifiers
Intermittent operation	Cold solder joints, connectors	Inspect solder joints; check board connectors; test ribbon cables

Reset: Power cycle amplifier to clear protection lockout.

Service: Authorized Marantz service centers only for warranty work.

Service Notes

Important service considerations and technical updates for the MA700 amplifier.

Thermal Management: Ensure proper heat sink compound application and mounting torque for output devices.

Bias Stability: Allow 30 minutes warm-up before final bias adjustment for thermal stability.

Component Matching: Output devices must be matched within 10% for optimal performance.

Safety Compliance: All service work must maintain original safety standards and isolation barriers.