Marantz PM34 Service Manuals

The Marantz PM34 is a high-quality stereo integrated amplifier featuring advanced audio circuitry, multiple input options, robust power output, and professional-grade components. This service manual provides comprehensive technical documentation for repair technicians, including schematics, alignment procedures, parts lists, and troubleshooting guides for proper maintenance and repair of the PM34 amplifier.

1. Technical Specifications 2. Block Diagrams 3. Circuit Descriptions 4. Alignment Procedures 5. Disassembly Instructions 6. Parts List 7. PCB Layouts 8. Wiring Diagrams 9. Troubleshooting Guide 10. Safety Precautions 11. Service Notes

Technical Specifications

Complete electrical and mechanical specifications for the Marantz PM34 integrated amplifier.

Parameter	Specification
Power Output	2 x 60W RMS (8Ω, 20Hz-20kHz)
Total Harmonic Distortion	<0.05% (1kHz, rated power)
Frequency Response	10Hz - 50kHz (+0/-3dB)
Input Sensitivity	Phono: 2.5mV, Line: 150mV
Signal-to-Noise Ratio	Phono: 75dB, Line: 95dB
Input Impedance	Phono: 47kΩ, Line: 50kΩ
Damping Factor	>100 (8Ω, 1kHz)
Tone Controls	Bass: ±10dB at 100Hz, Treble: ±10dB at 10kHz
Power Consumption	220W maximum
Dimensions	440 x 130 x 350mm (W x H x D)
Weight	8.5kg

Block Diagrams

System overview and signal flow diagrams showing the complete audio path from input to output stages.

Main System Block Diagram: Overall signal routing and control sections.
Power Supply Block Diagram: AC input to DC power distribution.
Pre-amplifier Section: Input selection, tone control, and volume control circuits.
Power Amplifier Section: Final amplification stages and protection circuits.
Protection Circuit Block Diagram: Speaker protection and thermal management.

NOTE: All block diagrams include component references for cross-referencing with schematics.

Circuit Descriptions

Detailed explanations of each major circuit section with component functions and signal processing.

Power Supply Circuit: Transformer, rectification, filtering, and regulation stages.
Phono Equalizer: RIAA equalization circuit with low-noise transistors.
Line Amplifier: High-level input amplification and buffer stages.
Tone Control Circuit: Bass and treble control networks with flat response bypass.
Power Amplifier: Complementary symmetry output stage with current mirror biasing.
Protection Circuit: DC detection, overload protection, and thermal shutdown.

CAUTION! High voltage present in power supply section - discharge capacitors before servicing.

Alignment Procedures

Step-by-step calibration and adjustment procedures for optimal performance.

DC Offset Adjustment: Adjust VR501/VR502 for 0mV ±5mV at speaker terminals.
Bias Current Adjustment: Set VR503/VR504 for 20mA across emitter resistors.
Phono Equalization: Verify RIAA response using test equipment.
Input Level Matching: Balance input sensitivities for consistent volume levels.
Protection Circuit Test: Verify proper operation of speaker protection relay.

Disassembly Instructions

Complete teardown procedure for accessing internal components.

Remove top cover: Unscrew 6 Phillips head screws from top panel.
Remove bottom cover: Turn unit upside down and remove 8 screws.
Front panel removal: Detach knobs and remove 4 front panel screws.
PCB access: Remove mounting screws for main board and preamp board.
Transformer removal: Disconnect wiring and remove mounting bolts.

WARNING! Always disconnect AC power before disassembly. Handle PCBs with care to avoid damage.

Parts List

Complete component listing with manufacturer part numbers and specifications.

Reference	Description	Part Number	Value/Specs
Q101-Q104	Transistor 2SC2240	MPSA42	NPN Low Noise
Q201-Q204	Transistor 2SA970	MPSA92	PNP Low Noise
Q501-Q504	Output Transistor 2SC3281	MJ21194	NPN Power
Q505-Q508	Output Transistor 2SA1302	MJ21193	PNP Power
C101-C104	Electrolytic Capacitor	ECE-A1CN100	10μF/50V
C501-C504	Electrolytic Capacitor	ECE-A1HN103	10000μF/63V
R101-R110	Carbon Film Resistor	MCF 1/4W	Various values
T001	Power Transformer	PM34-TRF-001	220V/2x28V

PCB Layouts

Printed circuit board diagrams showing component placement and trace routing.

Main Amplifier Board: Component side and solder side views with reference designators.
Pre-amplifier Board: Input selection and tone control circuit layout.
Power Supply Board: Rectification and filtering component placement.
Protection Circuit Board: Relay driver and detection circuit layout.
Front Panel Board: Switch and indicator LED placements.

Tip: Use magnifying glass for identifying small component designators on crowded boards.

Wiring Diagrams

Complete interconnection diagrams showing all internal wiring and external connections.

Main Harness Routing: Power supply to amplifier board connections.
Front Panel Wiring: Switch, potentiometer, and indicator connections.
Input/Output Connectors: RCA jacks, speaker terminals, and AC inlet wiring.
Grounding Scheme: Star grounding points and noise reduction techniques.
Shielded Cable Routing: Phono and line input cable shielding.

Troubleshooting Guide

Systematic approach to diagnosing and repairing common faults.

Symptom	Possible Cause	Corrective Action
No power	Fuse, power switch, transformer	Check F001/F002 fuses; verify AC voltage at transformer primary.
One channel dead	Output transistors, protection circuit	Check Q501-Q508; verify protection relay engagement.
Distortion	Bias current, DC offset, transistors	Adjust bias and offset; check driver transistors Q401-Q408.
Hum/buzz	Grounding, capacitors, shielding	Verify ground connections; check filter capacitors C501-C504.
No phono input	Phono EQ circuit, selector switch	Check Q101-Q104; verify switch S101 contacts.
Protection relay not engaging	DC offset, protection circuit fault	Measure DC offset at output; check Q601-Q604 in protection circuit.

Safety Precautions

Essential safety procedures for technicians working on high-power audio equipment.

WARNING! Lethal voltages present - always disconnect AC power before servicing. Use isolation transformer when testing live circuits. Discharge large capacitors before handling. Ensure proper grounding of test equipment.

Always work with discharged power supply capacitors.
Use appropriate personal protective equipment.
Verify insulation on all test probes and tools.
Follow electrostatic discharge (ESD) procedures for semiconductor devices.
Test with current-limited power supply when possible.

Service Notes

Additional technical information and field service observations.

Common Failures: Output transistors (2SC3281/2SA1302) prone to failure under short-circuit conditions.
Component Substitutions: MJ21193/MJ21194 suitable replacements for output devices.
Thermal Management: Ensure proper heatsink mounting and thermal compound application.
Factory Settings: Default bias current 20mA, DC offset 0mV.
Test Points: TP1/TP2 for bias measurement, TP3/TP4 for DC offset measurement.
Service Contact: Marantz authorized service centers for genuine parts and technical support.

Document Revision: 2.1 - Updated with component substitution information