Marantz PM 450 Service Manual

The Marantz PM 450 is a high-quality stereo integrated amplifier featuring 45 watts per channel, phono input for turntables, multiple audio inputs, tone controls, loudness contour, and headphone output. 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 3. Circuit Description 4. Alignment Procedures 5. Parts List 6. Schematic Diagrams 7. PCB Layouts 8. Mechanical Assembly 9. Troubleshooting Guide 10. Safety Precautions 11. Service Notes

Technical Specifications

Complete technical specifications for the Marantz PM 450 integrated amplifier.

Parameter	Specification
Power Output	45W + 45W (8Ω, 20Hz-20kHz)
Total Harmonic Distortion	0.02% (at rated output)
Frequency Response	10Hz-50kHz (+0/-3dB)
Input Sensitivity	Phono: 2.5mV, AUX: 150mV
Signal-to-Noise Ratio	Phono: 76dB, AUX: 100dB
Tone Controls	Bass: ±10dB at 100Hz, Treble: ±10dB at 10kHz
Power Supply	AC 120V/230V, 50/60Hz
Dimensions	440 x 130 x 330mm (W x H x D)
Weight	7.5kg
Power Consumption	180W maximum

Block Diagram

System block diagram showing signal flow and major functional blocks.

Input Selector: Phono, CD, Tuner, AUX switching
Phono Equalizer: RIAA equalization circuit
Tone Control: Bass and treble adjustment stages
Volume Control: ALPS potentiometer or electronic attenuator
Power Amplifier: Complementary symmetry output stage
Power Supply: Transformer, rectifier, and filter capacitors
Protection Circuit: DC detection and thermal protection

NOTE: Refer to schematic diagram for detailed component-level information.

Circuit Description

Detailed description of major circuit sections and their operation.

Phono Stage: MM cartridge compatible with 47kΩ loading
Preamplifier: Low-noise transistor or IC-based design
Tone Control: Baxandall-type bass and treble circuits
Power Amplifier: Direct-coupled complementary output
Protection: Speaker relay with DC offset detection
Power Supply: Dual rail ±35V DC for amplifier stages

CAUTION! High voltages present - discharge capacitors before servicing.

Alignment Procedures

DC Offset Adjustment: Adjust VR501/502 for 0mV ±5mV at speaker terminals
Bias Current Adjustment: Set VR503/504 for 15-20mA across emitter resistors
Phono Equalization: Verify RIAA response with test equipment
Input Level Matching: Adjust input sensitivity for uniform volume levels
Protection Circuit Test: Verify relay operation and protection timing
Tone Control Center: Ensure flat response at center detent positions

Parts List

Complete list of components with manufacturer part numbers and specifications.

Reference	Description	Part Number	Value/Specs
Q101-Q104	Transistor 2SC2240	2SC2240BL	NPN Low Noise
Q201-Q204	Transistor 2SA970	2SA970BL	PNP Low Noise
Q501-Q504	Output Transistor 2SC3281	2SC3281	NPN Power
Q505-Q508	Output Transistor 2SA1302	2SA1302	PNP Power
C101,C102	Electrolytic Capacitor	ECE-A1CN100	10μF/50V
C501,C502	Main Filter Capacitor	EET-ED2W680	6800μF/63V
R101,R102	Carbon Film Resistor	MFR-25SFF52	47kΩ 1/4W
F501,F502	Fuse	AGC-3	3A 250V

Schematic Diagrams

Complete schematic diagrams for all circuit boards and sections.

Main Amplifier Board: Power amplifier and protection circuits
Preamplifier Board: Input selection, phono stage, tone controls
Power Supply Board: Transformer, rectifiers, filter capacitors
Front Panel Board: Switches, indicators, and controls
Protection Circuit: Relay driver and DC detection

Tip: Use high-resolution prints for component identification and trace following.

PCB Layouts

Printed circuit board layouts with component placement and trace routing.

Component Side: Shows all component locations and reference designators
Solder Side: Displays copper traces and solder pads
Silkscreen: Component outlines and identification markings
Ground Planes: Indicates ground connections and shielding
Test Points: Locations for voltage measurements and signal injection

WARNING! Observe static discharge precautions when handling PCBs.

Mechanical Assembly

Exploded views and assembly instructions for mechanical components.

Part Number	Description	Quantity
CH-001	Main Chassis	1
FP-001	Front Panel Assembly	1
KN-001	Volume Knob	1
KN-002	Selector Knob	1
SC-001	Chassis Screw M4x8	6
SC-002	Board Screw M3x6	12
TR-001	Power Transformer	1
HS-001	Heat Sink Assembly	1

Troubleshooting Guide

Systematic approach to diagnosing and repairing common issues.

Symptom	Possible Cause	Corrective Action
No power	Fuse blown, power switch	Check/replace fuses F501,F502; verify switch operation
No sound	Protection relay, input selector	Check relay operation; verify input selection
Distortion	Bias current, DC offset	Adjust bias and DC offset; check output transistors
Hum/buzz	Grounding, filter capacitors	Check ground connections; replace filter capacitors
Intermittent operation	Cold solder joints, connectors	Resolder joints; clean and reseat connectors

Reset: Always verify bias and offset after component replacement.

Safety Precautions

Essential safety procedures for service technicians.

Always disconnect AC power before servicing. Discharge large capacitors. Use isolation transformer when testing live circuits. Observe component ratings and replacements. Ensure proper grounding. Use appropriate personal protective equipment.

CAUTION! Lethal voltages present - experienced technicians only.

Service Notes

Important service information and common modifications.

Original output transistors may be obsolete - use recommended substitutes
Electrolytic capacitors should be replaced after 15-20 years
Thermal compound should be refreshed when replacing output devices
Speaker protection relay contacts may require cleaning after extended use
Volume control potentiometer may develop noise - clean or replace
Factory service bulletins and updates should be consulted

Service Support: Contact authorized Marantz service centers for genuine parts and technical support.