Marantz MA-9S2 Service Manual

The Marantz MA-9S2 is a high-end monoblock power amplifier featuring advanced HDAM (Hyper Dynamic Amplifier Module) technology, dual power supplies, massive toroidal transformers, and premium component selection. This service manual covers technical specifications, circuit diagrams, adjustment procedures, troubleshooting, and maintenance guidelines for qualified service technicians.

1. Technical Specifications 2. Block Diagram & Circuit Overview 3. Disassembly Instructions 4. Adjustment Procedures 5. Power Supply Section 6. Amplifier Circuit 7. Protection Circuits 8. Test Points & Measurements 9. Troubleshooting Guide 10. Parts List 11. Safety Precautions

Technical Specifications

The MA-9S2 delivers exceptional audio performance with robust power output and minimal distortion.

Parameter	Specification
Power Output	300W RMS into 8Ω, 600W RMS into 4Ω
Frequency Response	5Hz - 100kHz (+0/-3dB)
Total Harmonic Distortion	<0.005% (20Hz-20kHz at rated power)
Input Sensitivity	1.2V for rated output
Input Impedance	47kΩ
Signal-to-Noise Ratio	120dB (A-weighted)
Damping Factor	>500 (20Hz-20kHz, 8Ω)
Power Consumption	650W maximum, 45W standby
Dimensions	440mm W × 195mm H × 482mm D
Weight	35kg

Block Diagram & Circuit Overview

The amplifier employs a fully balanced design from input to output stages.

Input Stage: HDAM-SA3 modules for high-speed signal processing
Voltage Amplification: Discrete differential amplifier with current mirror
Driver Stage: Complementary push-pull configuration
Output Stage: Multiple parallel power transistors for high current delivery
Power Supply: Dual-mono design with separate transformers

WARNING! High voltages present - discharge capacitors before servicing.

Disassembly Instructions

Proper disassembly procedure for safe access to internal components.

Remove top cover: 8 Phillips screws on rear and sides
Remove bottom plate: 6 screws for access to power supply
Front panel removal: 4 screws behind faceplate
Heat sink assembly: Requires removal of output transistors first

CAUTION! Handle circuit boards carefully to avoid damage to components.

Adjustment Procedures

DC Offset: Adjust VR101 for 0mV ±5mV at speaker terminals
Bias Current: Set VR102 for 50mV across emitter resistors
Power Supply Voltages: +75V and -75V rails (tolerance ±2V)
Protection Circuit: Verify operation at 2V DC offset threshold

Power Supply Section

Dual-mono power supply with independent regulation.

Main Transformer: 1000VA toroidal with electrostatic shield

Rectification: High-speed bridge rectifiers with snubber networks

Filtering: 40,000μF per channel with bypass capacitors

Regulation: Discrete regulators for front-end circuits

Amplifier Circuit

Fully complementary symmetry design with current feedback.

Input differential: Matched low-noise transistors
Voltage gain: High-speed complementary pairs
Driver stage: Temperature compensated bias network
Output stage: 6 pairs Sanken MT-200 power transistors

Tip: Use thermal compound when replacing output transistors.

Protection Circuits

Comprehensive protection systems for amplifier and speakers.

DC Detection: Triggers relay at >2V DC offset
Overcurrent Protection: Monitors output current
Thermal Protection: Thermal switch on heat sink
Overvoltage Protection: Zener diode clamping
Soft Start: Time-delay relay for power-on

WARNING! Do not bypass protection circuits during testing.

Test Points & Measurements

Designated test points for accurate measurement and diagnosis.

Test Point	Normal Value	Purpose
TP101	0V ±5mV	DC Offset adjustment
TP102	50mV ±10mV	Bias current measurement
TP103	+75V ±2V	Positive rail voltage
TP104	-75V ±2V	Negative rail voltage
TP105	+15V ±0.5V	Front-end supply

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
No output, protection LED on	DC offset, short circuit	Check output transistors, measure DC offset
Distorted sound	Bias current, damaged transistors	Adjust bias, check driver transistors
Hum in output	Ground loop, filter capacitors	Check grounding, test power supply capacitors
Intermittent operation	Thermal protection, loose connections	Check heat sink temperature, inspect solder joints
No power	Fuse, power switch, transformer	Check main fuse (8A), power switch continuity

Reset: Power cycle to reset protection circuits.

Parts List

Critical replacement components with Marantz part numbers.

Output Transistors: 2SC6011/2SA2151 (Sanken MT-200)
Power Transformer: T-1001 (1000VA toroidal)
Main Capacitors: C-801 (20,000μF/100V ×2)
Rectifier Diodes: D-401 (15A/200V bridge)
Fuses: F801 (8A slow-blow main), F802 (2A control)

Safety Precautions

High-voltage discharge procedure and safety guidelines.

CAUTION! Always discharge main capacitors through 100Ω/25W resistor before servicing. Use isolation transformer when testing live circuits. Ensure proper grounding of test equipment.

Service Contact: Authorized Marantz service centers only. For technical support, contact Marantz America at 1-800-370-3745 or visit www.marantz.com