Marantz Model 500 Service Manual

The Marantz Model 500 is a high-performance stereo power amplifier featuring 250 watts per channel RMS into 8 ohms, 20Hz to 20kHz with no more than 0.1% total harmonic distortion. This service manual provides comprehensive technical information, schematics, alignment procedures, and troubleshooting guidance for qualified service technicians. Below are key sections for specifications, block diagrams, circuit descriptions, alignment procedures, parts list, and service notes.

1. Technical Specifications 2. Block Diagrams 3. Circuit Description 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 electrical and mechanical specifications for the Marantz Model 500 power amplifier.

Parameter	Specification
Power Output	250W RMS per channel, 8 ohms, 20Hz-20kHz
Total Harmonic Distortion	<0.1% at rated power
Frequency Response	10Hz-50kHz (+0/-1dB)
Input Sensitivity	1.2V for rated output
Input Impedance	50k ohms
Signal-to-Noise Ratio	>110dB (A-weighted)
Damping Factor	>200 at 8 ohms
Power Requirements	120V AC, 60Hz, 750W max
Dimensions	19" W x 7" H x 15" D
Weight	45 lbs (20.4 kg)

Block Diagrams

System block diagrams showing signal flow and power distribution.

Main Amplifier Block Diagram: Input stage, driver stage, output stage, protection circuits.
Power Supply Block Diagram: Transformer, rectifier, filter capacitors, regulation.
Protection Circuit Block Diagram: DC detection, thermal protection, current limiting.
Control Circuit Block Diagram: Input selector, level control, muting circuit.

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

Circuit Description

Detailed description of all major circuit sections and their operation.

Input Stage: Differential amplifier with current mirror load.
Voltage Amplifier Stage: High-speed voltage amplifier with frequency compensation.
Output Stage: Complementary Darlington configuration with multiple output transistors.
Power Supply: Dual secondary transformer with bridge rectifiers and large filter capacitors.
Protection Circuits: DC offset protection, thermal shutdown, soft-start circuit.

CAUTION! Always discharge power supply capacitors before working on amplifier circuits.

Alignment Procedures

Bias Current Adjustment: Adjust VR501/VR502 for 30mV across emitter resistors.
DC Offset Adjustment: Adjust VR503/VR504 for 0V ±10mV at output terminals.
Protection Circuit Check: Verify proper operation of all protection systems.
Power Supply Voltages: Verify ±75V DC rails are within 5% tolerance.
Input Sensitivity: Verify 1.2V input produces 250W output into 8 ohm load.

Parts List

Complete listing of all components with manufacturer part numbers and specifications.

Semiconductors: 2SC2240, 2SA970 (input stage), 2SC2705, 2SA1145 (driver), 2SC3281, 2SA1302 (output).

Resistors: Metal film 1/4W and 1/2W types. Capacitors: Electrolytic, film, and ceramic types. Transformers: Main power transformer T001. Connectors: Input/output connectors, power connector.

Schematic Diagrams

Detailed schematic diagrams for all circuit boards and subsystems.

Main Amplifier Schematic: Complete left and right channel amplifier circuits.
Power Supply Schematic: Transformer, rectifiers, filter circuits, protection.
Protection Circuit Schematic: DC detection, relay driver, thermal protection.
Control Board Schematic: Input switching, level control, indicator circuits.

Tip: Use original Marantz replacement parts for optimal performance and reliability.

Mechanical Assembly

Exploded views and assembly instructions for chassis and internal components.

Chassis Disassembly: Step-by-step removal of top cover, front panel, and circuit boards.
Heat Sink Assembly: Proper mounting and thermal compound application for output transistors.
Transformer Mounting: Secure mounting with proper isolation and grounding.
Board Installation: Correct orientation and secure fastening of all PC boards.
Wiring Harness: Proper routing and connection of all internal wiring.

WARNING! Ensure all safety grounds are properly connected during reassembly.

Troubleshooting Guide

Systematic approach to diagnosing and repairing common problems.

Symptom	Possible Cause	Corrective Action
No power	Blown fuse, faulty power switch	Check F001/F002; replace if blown; check power switch operation.
Distorted output	Bias current incorrect, faulty output transistors	Adjust bias current; test output transistors; replace if shorted.
DC offset high	Input stage imbalance, faulty differential pair	Adjust DC offset; replace Q101/Q102 if out of specification.
Protection relay not engaging	DC detection circuit fault, relay driver failure	Check DC detection circuit; test relay driver transistors Q701/Q702.
Intermittent operation	Cold solder joints, faulty connectors	Inspect for cold solder joints; reseat all connectors and cables.

Service Notes

Important service tips and modifications from Marantz technical support.

Updated bias procedure for improved thermal stability. Recommended replacement transistors for obsolete parts. Modified protection circuit timing for better reliability. Improved grounding scheme for reduced hum and noise.

Safety Precautions

Critical safety information for service technicians.

CAUTION! Lethal voltages present even when unit is disconnected from AC power. Always discharge power supply capacitors before servicing. Use isolation transformer when testing live circuits. Follow proper electrostatic discharge (ESD) procedures when handling semiconductors.

Warranty Information

Marantz limited warranty terms and service center information.

Marantz Model 500 carries a 3-year limited warranty on parts and labor. Warranty applies to original purchaser only and excludes damage from misuse, improper installation, or unauthorized modifications. For warranty service, contact authorized Marantz service center. For technical support, visit www.marantz.com or contact 1-800-270-2748.