Marantz 2240 Service Manual

The Marantz 2240 is a classic stereo receiver from the 1970s featuring 40 watts per channel RMS power, high-quality analog circuitry, FM/AM tuner, phono inputs for turntables, tape monitoring, loudness control, and distinctive Marantz styling with blue dial lights and wood cabinet. This service manual provides technical specifications, circuit diagrams, alignment procedures, troubleshooting guides, and maintenance instructions for qualified service technicians.

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

Technical Specifications

Complete electrical and performance specifications for the Marantz 2240 stereo receiver.

Parameter	Specification
Power Output	40 watts per channel RMS (8 ohms, 20Hz-20kHz)
Total Harmonic Distortion	0.3% or less at rated output
Frequency Response	10Hz-50kHz (+1, -3dB)
Input Sensitivity	Phono: 2.5mV; Aux: 250mV; Tape: 250mV
Signal-to-Noise Ratio	Phono: 70dB; Aux: 85dB
Tuner Section	FM/AM with multiplex stereo
Dimensions	17-3/8" W × 5-3/4" H × 14-1/2" D
Weight	24.2 lbs (11 kg)
Power Requirements	120V AC, 60Hz, 200W
Speaker Impedance	4-16 ohms

Block Diagram Overview

System block diagram showing signal flow and major circuit sections.

Input Selector: Phono, Aux, Tape 1, Tape 2, FM, AM
Phono Equalizer: RIAA equalization circuit
Tone Control: Bass, Treble, Loudness controls
Power Amplifier: Complementary symmetry output stage
Power Supply: Transformer, rectifiers, regulators
Tuner Section: FM front end, IF, detector, MPX
Protection Circuit: Speaker protection relay

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

Circuit Descriptions

Detailed description of major circuit sections and their operation.

Power Supply: Dual secondary transformer with full-wave rectification providing ±35V DC to amplifier sections
Phono Preamplifier: Discrete transistor design with precise RIAA equalization
Power Amplifier: Direct-coupled complementary output with current mirror drivers
Protection Circuit: DC detection and time-delay relay for speaker protection
Tone Control: Passive bass and treble controls with loudness compensation
FM Tuner: 3-gang variable capacitor, 3-stage IF amplification, ratio detector

Alignment Procedures

Step-by-step alignment instructions for tuner and amplifier sections.

FM IF Alignment: Connect sweep generator to FM detector output
FM Front End: Align RF and oscillator circuits for proper tracking
FM Multiplex: Adjust 19kHz and 38kHz circuits for stereo separation
AM Alignment: Set IF transformers and antenna trimmer
DC Offset: Adjust for 0mV DC at speaker terminals
Bias Current: Set idle current to specified value

CAUTION! Use proper test equipment and follow procedures exactly.

Voltage Measurements

Reference voltage measurements at key test points with normal operation.

Test Point	Voltage (DC)	Notes
Power Supply +B	+35V	Main positive rail
Power Supply -B	-35V	Main negative rail
Speaker Output	0V ±50mV	DC offset measurement
Phono Stage Supply	+24V	Regulated supply
Tuner Supply	+12V	Regulated supply
Protection Circuit	+24V	Relay drive voltage

Parts List

Complete listing of components with manufacturer part numbers.

Transistors: 2SC458, 2SA726, 2SC945, 2SA733 (critical replacements)
Diodes: 1S2473, 1S1555, WZ-130 zener diodes
Capacitors: Electrolytic: 2200µF/50V, 100µF/80V; Film: 0.47µF/100V
Resistors: Carbon film 1/4W and 1/2W types
Potentiometers: Volume, balance, tone controls
Output Transistors: 2N3055/MJ2955 complementary pair

Schematic Diagrams

Complete schematic diagrams for all circuit boards.

Main Amplifier Board (P700)
Power Supply Board (P800)
Tone Control Board (P900)
Phono Equalizer Board (P400)
FM Tuner Board (P300)
AM Tuner Board (P200)
Protection Circuit Board (P600)

Note: Schematics show component values, transistor types, and wiring connections.

PCB Layouts

Printed circuit board layouts showing component placement and traces.

Component side and solder side views
Test point locations clearly marked
Ground and power supply traces highlighted
Critical signal paths identified
Board-to-board connector pinouts

Tip: Use layouts with schematics for efficient troubleshooting.

Troubleshooting Guide

Common problems and solutions for the Marantz 2240.

Symptom	Possible Cause	Corrective Action
No sound from both channels	Protection relay not engaging	Check power supply voltages; test protection circuit
Distorted audio	DC offset incorrect; bias current wrong	Adjust DC offset and bias current per procedure
One channel dead	Output transistor failure	Test output transistors; check driver stage
Hum in phono	Grounding issue; capacitor failure	Check ground connections; replace filter capacitors
FM stereo not working	MPX circuit alignment	Realign multiplex decoder circuit
Lights out	Dial lamp failure	Replace 8V, 300mA dial lamps

Service Adjustments

Routine service adjustments and calibration procedures.

DC Balance Adjustment: Set for minimum DC at output
Bias Current Adjustment: Set to 20mA per output pair
FM Stereo Separation: Adjust for maximum separation
FM Tuning Meter: Calibrate for center tuning
Signal Strength Meter: Adjust for proper indication
Output Level: Set for rated power with distortion analyzer

WARNING! Use isolation transformer when making live measurements.

Safety Precautions

Important safety information for service technicians.

Always disconnect AC power before working on unit
Discharge large capacitors before testing circuits
Use Variac for initial power-up after repairs
Replace safety-critical components with exact specifications
Check for proper grounding and insulation
Verify all covers and shields are reinstalled

Service Note: This manual is intended for qualified service personnel only. Unauthorized service may void warranty and create safety hazards.