Marantz 1200 Service Manual

The Marantz 1200 is a high-performance stereo receiver featuring 120 watts per channel RMS, advanced tuner section with quartz PLL synthesizer tuning, comprehensive input/output connectivity, and professional-grade audio circuitry. This service manual provides detailed technical information for qualified service technicians, including schematics, alignment procedures, parts lists, and troubleshooting guidelines for proper maintenance and repair.

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

Technical Specifications

Complete electrical and mechanical specifications for the Marantz 1200 stereo receiver.

Parameter	Specification
Power Output	120W RMS per channel (8Ω, 20Hz-20kHz)
Total Harmonic Distortion	<0.05% at rated output
Frequency Response	10Hz-50kHz (+0/-1dB)
Input Sensitivity	Phono: 2.5mV; Aux: 150mV
Signal-to-Noise Ratio	Phono: 75dB; Aux: 95dB
Tuner Section	Quartz PLL synthesizer, FM/AM
FM Sensitivity	1.8μV (IHF)
Dimensions	19" W × 6.75" H × 16.5" D
Weight	48 lbs (21.8 kg)
Power Requirements	120V AC, 60Hz, 650W max

Block Diagrams

System block diagrams showing signal flow and power distribution.

Main System Block Diagram: Overview of all major sections
Amplifier Section: Power amplifier and protection circuits
Tuner Section: FM/AM tuner and PLL circuitry
Power Supply: Main transformer and regulation circuits
Control Section: Front panel and switching circuits

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

Circuit Descriptions

Detailed explanation of major circuit sections and their operation.

Power Amplifier Circuit: Complementary symmetry output stage with current mirror
Preamplifier Section: Phono equalization and line-level amplification
Tuner Circuits: FM front end, IF stages, and stereo decoder
Power Supply: Dual secondary transformer with regulated supplies
Protection Circuits: DC offset protection and thermal monitoring

WARNING! High voltages present - exercise extreme caution when servicing.

Alignment Procedures

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

FM Tuner Alignment: RF front end, IF stages, and multiplex decoder
AM Tuner Alignment: RF and IF alignment procedures
Amplifier Bias Adjustment: Idle current and DC offset settings
Protection Circuit Calibration: DC detection and thermal protection
Meter Calibration: Power output and tuning meter adjustment

Disassembly Instructions

Proper disassembly sequence for accessing internal components.

Remove top cover: Four screws on rear panel
Remove front panel: Six screws along top and bottom edges
Access main board: Remove shield covers and mounting screws
Remove tuner assembly: Disconnect wiring harness and mounting hardware
Access power supply: Remove heat sink and transformer mounting bolts

CAUTION! Large capacitors may retain charge - discharge before servicing.

Parts List

Complete component listing with manufacturer part numbers.

Component	Part Number	Description
Output Transistors	2SC2581/2SA1106	Complementary power transistors
Main Filter Caps	CE85 10000μF/80V	Dual main power supply capacitors
Power Transformer	T001-001	Dual secondary custom transformer
Tuner IC	LA1235	FM IF amplifier and detector
Decoder IC	LA3401	FM stereo multiplex decoder

Schematic Diagrams

Complete schematic diagrams for all circuit boards.

Main Amplifier Schematic: Power output and driver stages
Preamplifier Schematic: Phono and line-level circuits
Tuner Schematic: FM/AM tuner and control circuits
Power Supply Schematic: Main and regulated supplies
Protection Circuit Schematic: Speaker protection and thermal circuits

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

PCB Layouts

Printed circuit board layouts and component placement guides.

Main Amplifier Board: Component side and solder side views
Preamplifier Board: Input switching and tone control circuits
Tuner Board: FM/AM tuner component placement
Power Supply Board: Rectifier and filter component layout
Control Board: Front panel switch and indicator circuits

Troubleshooting Guide

Systematic troubleshooting procedures for common issues.

Symptom	Possible Cause	Corrective Action
No power	Fuse, power switch, transformer	Check main fuse; verify AC input; test transformer primary
Distorted audio	Bias current, output transistors	Adjust bias current; test output transistors; check driver stage
No FM reception	Tuner power, RF stage, local oscillator	Verify tuner voltages; check RF transistors; test oscillator
Protection engaged	DC offset, thermal fault	Measure DC offset; check thermal sensor; inspect protection relay
Hum/buzz	Grounding, filter capacitors	Check ground connections; test filter capacitors; verify shielding

Service Notes

Important service information and common repair procedures.

Common issues: Output transistor failure due to bias drift; power supply capacitor aging; tuner alignment drift over time. Recommended upgrades: Replace electrolytic capacitors in power supply; upgrade thermal compound on heat sinks; install modern protection components where applicable.

WARNING! Always use isolation transformer when servicing live circuits.

Safety Precautions

Critical safety information for service personnel.

High voltage warning: Lethal voltages present in power supply and amplifier sections. Always discharge large capacitors before servicing. Use proper grounding techniques. Follow ESD precautions when handling sensitive components. Verify all safety certifications after repair completion.

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