Marantz 2240B Service Manual

The Marantz 2240B is a classic stereo receiver from the 1970s featuring 40 watts per channel, high-quality amplification, FM/AM tuner, phono input for turntables, tape monitoring, loudness control, and tone adjustments. This service manual provides comprehensive technical information for service technicians, including schematics, alignment procedures, parts lists, and troubleshooting guides for proper maintenance and repair.

1. Technical Specifications 2. Block Diagram Overview 3. Circuit Descriptions 4. Alignment Procedures 5. Parts List 6. Schematic Diagrams 7. PCB Layouts 8. Troubleshooting Guide 9. Service Adjustments 10. Safety Precautions 11. Contact Information

Technical Specifications

Complete technical specifications for the Marantz 2240B stereo receiver.

Parameter	Specification
Power Output	40 watts per channel (8 ohms, 20Hz-20kHz)
Total Harmonic Distortion	0.1% at rated output
Frequency Response	10Hz - 50kHz (+0, -1dB)
Input Sensitivity	Phono: 2.0mV, Aux: 250mV
Signal-to-Noise Ratio	Phono: 75dB, Aux: 90dB
Tuner Section	FM/AM with multiplex stereo
Dimensions	17-3/8" W × 5-3/4" H × 14-1/4" D
Weight	26.5 lbs (12 kg)
Power Requirements	120V AC, 60Hz, 180W

Block Diagram Overview

System block diagram showing signal flow and major circuit sections.

Input Selector: Phono, Aux, Tuner, Tape
Preamplifier Stage: Phono equalization and line amplification
Tone Control: Bass, Treble, and Loudness circuits
Power Amplifier: Dual-channel 40W output stage
Power Supply: Transformer, rectification, and regulation
Protection Circuit: Speaker protection and thermal safety

NOTE: Refer to schematic diagrams for detailed circuit analysis.

Circuit Descriptions

Detailed descriptions of major circuit sections and their operation.

Power Supply: Transformer T001, bridge rectifier, capacitor filtering
Preamplifier: Phono EQ using IC201, line stage amplification
Tone Control: Bass and treble controls with loudness compensation
Power Amplifier: Complementary symmetry output stage with driver transistors
Protection Circuit: Relay-based speaker protection and DC offset detection
Tuner Section: FM front end, IF amplification, and multiplex decoder

Alignment Procedures

Step-by-step alignment procedures for optimal performance.

FM Tuner Alignment: Adjust RF, mixer, and IF stages for maximum sensitivity
AM Tuner Alignment: Set oscillator and antenna trimmers
Stereo Decoder: Adjust separation and pilot cancellation
Phono Equalization: Verify RIAA curve accuracy
DC Offset: Adjust bias and offset voltages in power amplifier
Power Supply: Verify all DC voltages within specification

WARNING! Use proper test equipment and follow safety procedures.

Parts List

Complete list of components with manufacturer part numbers.

Component	Part Number	Description
Power Transformer	Marantz T001	Power supply transformer
Output Transistors	2SC1116	NPN power transistor
Driver Transistors	2SA726	PNP driver transistor
IC Phono Preamp	HA1451	Phono equalization IC
Filter Capacitors	6800μF/50V	Main power supply capacitors
Relay	MY4-02-DC24	Speaker protection relay

Schematic Diagrams

Complete schematic diagrams for all circuit sections.

Main Amplifier Schematic: Power amplifier and protection circuits
Preamplifier Schematic: Phono and line stage circuits
Power Supply Schematic: Transformer, rectification, and regulation
Tuner Schematic: FM/AM tuner and stereo decoder
Control Schematic: Selector switches, tone controls, and volume

NOTE: Schematics show component values, test points, and voltage readings.

PCB Layouts

Printed circuit board layouts for component placement and tracing.

Main Amplifier Board: Component side and solder side views
Preamplifier Board: Phono and tone control circuits
Power Supply Board: Rectification and filtering components
Tuner Board: FM/AM tuner section layout
Control Board: Selector switches and potentiometers

Tip: Use layouts for component identification and board repair.

Troubleshooting Guide

Common problems and solutions for the Marantz 2240B.

Symptom	Possible Cause	Corrective Action
No sound output	Protection relay, blown fuses	Check relay operation, replace fuses, test output transistors
Distorted audio	Bias adjustment, bad transistors	Adjust bias voltage, replace output/driver transistors
No FM reception	Tuner alignment, bad IC	Realign FM section, replace tuner IC HA1156
Hum in audio	Filter capacitors, ground issues	Replace main filter capacitors, check ground connections
Intermittent operation	Cold solder joints, switches	Resolder connections, clean selector switches

Service Adjustments

Critical adjustments for proper receiver operation.

DC Offset: Adjust for 0V DC at speaker outputs
Bias Current: Set idle current to specified value
FM Tuner: Adjust for maximum sensitivity and stereo separation
Phono EQ: Verify RIAA equalization accuracy
Meter Calibration: Adjust signal strength and tuning meters

CAUTION! Use insulated tools and follow proper safety procedures.

Safety Precautions

Important safety information for service technicians.

Always disconnect power before servicing. Use isolation transformer when working on live circuits. Discharge large capacitors before handling. Follow proper grounding procedures. Use appropriate personal protective equipment.

WARNING! High voltages present - risk of electric shock. Lethal voltages exist in power supply and amplifier sections.

Contact Information

For technical support and replacement parts.

Marantz America, Inc. • 1100 Maplewood Drive • Itasca, IL 60143 • Phone: 1-800-270-2744 • Website: www.marantz.com

This service manual is intended for qualified service technicians only. Unauthorized modifications may void warranty and create safety hazards.