Marantz Model 2245 Service Manual

The Marantz Model 2245 is a classic stereo receiver from the 1970s featuring 45 watts per channel RMS, high-quality analog tuning, phono inputs for turntables, tape monitoring, loudness compensation, and distinctive blue backlit tuning dial. This service manual covers technical specifications, circuit diagrams, alignment procedures, troubleshooting, and maintenance guidelines for qualified service technicians.

1. Technical Specifications 2. Block Diagrams 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 electrical and mechanical specifications for the Marantz 2245 stereo receiver.

Parameter	Specification
Power Output	45 watts per channel RMS (8 ohms, 20Hz-20kHz)
Total Harmonic Distortion	0.3% or less at rated output
Frequency Response	10Hz - 50kHz (+0, -3dB)
Input Sensitivity	Phono: 2.5mV; Aux: 250mV
Signal-to-Noise Ratio	Phono: 70dB; Aux: 90dB
Tuning Range	FM: 88-108MHz; AM: 530-1620kHz
Dimensions	17-3/8" W × 5-3/4" H × 14-3/4" D
Weight	26.5 lbs (12 kg)
Power Requirements	120V AC, 60Hz, 280W
Speaker Impedance	4-16 ohms

Block Diagrams

System block diagrams showing signal flow and major functional sections.

Main Amplifier Block Diagram: Preamp, tone control, power amplifier sections
Tuner Section Block Diagram: RF amplifier, mixer, IF stages, detector
Power Supply Block Diagram: Transformer, rectifier, regulator circuits
Control Section Block Diagram: Selector switches, volume, balance controls

NOTE: All diagrams show signal paths and interconnection points between modules.

Circuit Descriptions

Detailed explanations of major circuit functions and operation.

Power Amplifier Circuit: Complementary symmetry output stage with protection
Phono Equalizer: RIAA equalization with low-noise transistor design
Tone Control Circuit: Bass and treble controls with center detents
FM Tuner Section: FET front end, ceramic filters, phase-locked loop multiplex
Power Supply: Dual voltage rails with overcurrent protection

CAUTION! High voltages present - discharge capacitors before servicing.

Alignment Procedures

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

FM Tuner Alignment: RF stages, IF strip, detector, multiplex
AM Tuner Alignment: Oscillator and antenna trimmers
Phono Equalization: RIAA frequency response verification
Power Amplifier Bias: DC offset and idle current adjustment
Meter Calibration: Tuning meter and power output meter

Parts List

Complete component listing with manufacturer part numbers and substitutions.

Reference Designator	Description	Part Number	Substitution
Q701-Q704	Output Transistor	2SC1116	MJ21193G
C001-C002	Main Filter Capacitor	6800μF/63V	6800μF/80V
R201-R204	Emitter Resistor	0.47Ω/5W	0.47Ω/7W
D701-D704	Rectifier Diode	1S1886	1N4007
F701	Main Fuse	4A/250V	4A/250V Slow-Blow

Schematic Diagrams

Complete schematic diagrams for all circuit boards and modules.

Main Amplifier Schematic: P700 board - power output stage
Preamp/Tone Control Schematic: P800 board - input switching and tone circuits
FM Tuner Schematic: P300 board - FM front end and IF stages
Power Supply Schematic: P900 board - transformer and regulation
Control Assembly Schematic: Front panel switches and indicators

Tip: Use high-quality prints for best component identification.

PCB Layouts

Printed circuit board layouts showing component placement and traces.

Main Amplifier Board (P700): Component side and solder side views
Preamp Board (P800): With ground plane identification
Tuner Board (P300): Shielded compartment layouts
Power Supply Board (P900): High-current trace patterns
Control Board (P100): Switch and potentiometer mounting

Troubleshooting Guide

Systematic approach to diagnosing and repairing common problems.

Symptom	Possible Cause	Corrective Action
No power	Blown fuse, power switch	Check F701, F702; test power switch S901
Distorted audio	Bias current, output transistors	Adjust bias per procedure; test Q701-Q704
No FM reception	RF stage, power supply	Check voltages on P300; test FET Q301
Hum in output	Filter capacitors, ground	Replace C001, C002; check ground connections
Intermittent operation	Cold solder joints, connectors	Resolder main boards; clean all connectors

Service Adjustments

Critical adjustment points and procedures for optimal performance.

DC Offset Adjustment: VR701 for 0V DC at speaker terminals
Idle Current Adjustment: VR702 for 20mA per output pair
FM Detector Alignment: T302 for minimum distortion
Stereo Separation Adjustment: VR301 for maximum separation
Meter Zero Adjustment: Mechanical zeroing of tuning meter

WARNING! Use insulated tools and follow all safety procedures.

Safety Precautions

Essential safety information for technicians working on high-voltage equipment.

Always disconnect AC power before servicing. Discharge main filter capacitors (C001, C002) before touching circuits. Use isolation transformer when testing live circuits. Replace safety-critical components with identical specifications. Ensure proper grounding of all test equipment.

CAUTION! Lethal voltages present - experienced technicians only.

Contact Information

Manufacturer support and service center information.

Marantz America, Inc. • 1100 Maplewood Drive • Itasca, IL 60143 • Service Department: 1-800-270-2743 • Technical Support Fax: 1-630-741-0337 • For genuine Marantz parts, contact authorized service centers only.