Marantz 3650 Service Manual

The Marantz 3650 is a professional stereo preamplifier featuring high-quality audio performance, multiple input selections, tone controls, tape monitoring, and advanced circuitry design. This service manual provides comprehensive technical information for service technicians, including schematics, alignment procedures, parts lists, and troubleshooting guidelines for proper maintenance and repair.

1. Technical Specifications 2. Block Diagram Overview 3. Circuit Description 4. Alignment Procedures 5. Parts List 6. Schematic Diagrams 7. Mechanical Assembly 8. Troubleshooting Guide 9. Service Notes 10. Safety Precautions

Technical Specifications

Complete electrical and performance specifications for the Marantz 3650 stereo preamplifier.

Parameter	Specification
Frequency Response	10Hz - 100kHz ±0.5dB
Total Harmonic Distortion	<0.05% at 1kHz
Signal-to-Noise Ratio	>90dB (IHF-A weighted)
Input Sensitivity	2.5mV (Phono), 150mV (High Level)
Input Impedance	47kΩ (Phono), 100kΩ (High Level)
Output Level	1.5V (Main Out)
Tone Control Range	±10dB at 100Hz and 10kHz
Power Requirements	120V AC, 60Hz, 15W
Dimensions	420mm W × 110mm H × 310mm D
Weight	6.5kg

Block Diagram Overview

Functional block diagram showing signal flow and major circuit sections.

Input Selector: Phono, Tuner, Aux, Tape 1, Tape 2
Phono Equalization: RIAA compensation network
Tone Control: Bass and Treble adjustment circuits
Volume/Balance: Dual concentric controls
Output Stage: Buffer amplifier and main output
Power Supply: Regulated ±15V DC rails

NOTE: All signal paths are fully balanced for minimum noise.

Circuit Description

Detailed analysis of major circuit sections and their operation.

Input Stage: JFET differential amplifier with low noise characteristics
Phono Preamp: Discrete transistor design with precise RIAA equalization
Tone Control: Baxandall-type circuit with selectable turnover frequencies
Power Supply: Dual secondary transformer with bridge rectifiers and regulators
Protection Circuitry: DC offset protection and muting relay

CAUTION! High voltages present - discharge capacitors before servicing.

Alignment Procedures

Step-by-step calibration and adjustment procedures.

DC Offset Adjustment: Adjust VR101/VR102 for 0V DC at output
Phono Equalization: Verify RIAA response with test equipment
Tone Control Center: Set bass and treble controls to flat response
Power Supply Voltages: Verify ±15V DC at test points TP1/TP2
Input Sensitivity: Calibrate using 1kHz test signal

WARNING! Use calibrated test equipment for all adjustments.

Parts List

Complete component listing with manufacturer part numbers.

Reference	Description	Part Number
Q101-Q104	Transistor 2SC2240	MAR-2240
Q105-Q108	Transistor 2SA970	MAR-970
IC101, IC102	Op-amp NJM2068	MAR-2068
C101-C104	Capacitor 100μF/25V	MAR-EL100
R101-R110	Resistor 10kΩ 1%	MAR-MF10K
VR101, VR102	Trimmer 500Ω	MAR-TR500
F101	Fuse 1A Slow Blow	MAR-F1A

Schematic Diagrams

Complete schematic diagrams for all circuit boards.

Main Amplifier Board: Schematic MAR-3650-MAIN
Power Supply Board: Schematic MAR-3650-PWR
Control Board: Schematic MAR-3650-CTRL
Input Selector: Schematic MAR-3650-INPUT

Tip: Refer to component layout diagrams for physical locations.

Mechanical Assembly

Disassembly and reassembly instructions with exploded views.

Remove top cover: Four screws on rear panel
Front panel removal: Two screws on each side
Circuit board access: Remove mounting screws
Knob removal: Pull straight off shafts
Selector switch removal: Remove nut and washer

CAUTION! Handle PC boards by edges to avoid damage.

Troubleshooting Guide

Systematic approach to diagnosing and repairing common issues.

Symptom	Possible Cause	Corrective Action
No output	Power supply failure	Check fuse F101; measure ±15V rails
Distorted sound	DC offset incorrect	Adjust VR101/VR102; check transistors
Hum/buzz	Ground loop/capacitor	Check ground connections; replace C101-C104
Intermittent operation	Cold solder joints	Resolder all connections on main board
Phono input dead	RIAA circuit failure	Check Q101-Q104; verify RIAA network

Service Notes

Important technical notes and modifications from manufacturer.

Revision 2: Updated power supply capacitors for improved reliability
Service Bulletin 3650-1: Replace Q105-Q108 with matched pairs
Performance Tip: Use low-noise transistors for phono stage
Calibration: Allow 30 minutes warm-up before adjustments

NOTE: Always verify serial number for applicable revisions.

Safety Precautions

Essential safety procedures for service personnel.

Always disconnect AC power before servicing. Use isolation transformer when testing live circuits. Discharge large capacitors before handling. Wear safety glasses when working with high voltages. Follow ESD precautions when handling semiconductors.

WARNING! Lethal voltages present - qualified technicians only.