Marantz 2385 Service Manual

The Marantz 2385 is a high-performance stereo receiver from the classic Marantz line, featuring 185 watts per channel, dual power meters, phono inputs, tuner section with FM/AM reception, multiple audio inputs/outputs, tone controls, loudness compensation, and sophisticated protection circuits. 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. Disassembly Instructions 6. Test Points & Measurements 7. Troubleshooting Guide 8. Parts List 9. Schematics 10. PCB Layouts 11. Safety Precautions

Technical Specifications

Complete technical specifications and performance characteristics of the Marantz 2385 stereo receiver.

Parameter	Specification
Power Output	185 watts per channel (8 ohms, 20Hz-20kHz)
Total Harmonic Distortion	0.05% at rated output
Frequency Response	5Hz-50kHz (+0, -1dB)
Input Sensitivity	Phono: 2.5mV; Aux: 250mV
Signal-to-Noise Ratio	Phono: 75dB; Aux: 95dB
Damping Factor	60 at 8 ohms
Tuner Section	FM/AM with quartz locking
FM Sensitivity	1.8uV (IHF)
Power Requirements	120V AC, 60Hz, 750W max
Dimensions	19-1/4" W x 7-1/4" H x 17-1/2" D

Block Diagrams

System block diagrams showing signal flow and functional relationships between circuit sections.

Main System Block Diagram: Overview of entire receiver architecture
Power Amplifier Block: Dual mono power amplifier configuration
Preamplifier Section: Phono, tone control, and input switching
Tuner Block Diagram: FM/AM tuner with multiplex decoder
Power Supply Block: Multiple regulated voltage supplies
Protection Circuit: Speaker protection and thermal management

WARNING! For qualified technicians only. High voltages present - exercise extreme caution.

Circuit Descriptions

Detailed circuit analysis and operational theory for each major section.

Power Amplifier Circuit: Complementary symmetry output stage with current mirror
Phono Equalizer: RIAA equalization with low-noise FET inputs
Tone Control: Bass and treble controls with turnover selection
FM Tuner: Phase locked loop multiplex with ceramic filters
Power Supply: Dual secondary transformer with multiple regulators
Protection System: DC detection, overload, and thermal protection

CAUTION! Always discharge power supply capacitors before servicing.

Alignment Procedures

FM Tuner Alignment: IF alignment, limiter adjustment, multiplex separation
AM Tuner Alignment: IF and RF alignment procedures
Phono Equalization: RIAA response verification and adjustment
Power Amplifier Bias: Idle current adjustment and DC offset
Meter Calibration: Power meter and tuning meter calibration
Protection Circuit: Trip point adjustment and verification
Required Equipment: Audio generator, oscilloscope, distortion analyzer, VTVM

Disassembly Instructions

Step-by-step disassembly guide for accessing internal components.

Procedure: Remove top cover, front panel, bottom cover, circuit boards in sequence.

Remove rear panel screws and lift top cover
Detach front panel knobs and remove mounting screws
Remove bottom panel for access to power supply
Disconnect wiring harnesses carefully noting positions
Remove main amplifier heat sinks for output transistor replacement
Extract tuner assembly for alignment access

Test Points & Measurements

Critical test points and expected voltage/current measurements.

Test Point	Location	Expected Value
TP1: +B Supply	Power Supply Board	+65V DC ±2V
TP2: -B Supply	Power Supply Board	-65V DC ±2V
TP3: +48V Reg	Protection Board	+48V DC ±1V
TP4: +15V Reg	Control Board	+15V DC ±0.5V
TP5: Amplifier Offset	Output Terminals	±15mV DC max
TP6: Bias Current	Emitter Resistors	30mA ±5mA

Troubleshooting Guide

Systematic troubleshooting procedures for common failure modes.

Symptom	Possible Cause	Corrective Action
No power	Fuse, power switch, transformer	Check main fuse F801; verify AC input; test power transformer
Protection relay not engaging	DC offset, protection circuit fault	Measure DC offset at outputs; check protection IC P01
Distorted audio	Output transistors, bias current	Test output pairs Q701-Q704; adjust bias current
No FM reception	Tuner section, power supply	Verify +15V to tuner; check FM front end transistors
Hum in phono	Grounding, capacitor failure	Check phono ground; replace filter capacitors C101/C102
Meters not working	Meter drive circuit, power supply	Test meter movement; check driver transistors Q001-Q004

Parts List

Complete component listing with manufacturer part numbers and substitutions.

Semiconductors: Transistors, diodes, ICs with original Marantz part numbers
Capacitors: Electrolytic, film, ceramic with voltage and tolerance ratings
Resistors: Carbon film, metal oxide with wattage specifications
Mechanical Parts: Switches, pots, knobs, hardware
Transformers: Power, output with electrical specifications
Special Components: Tuning capacitor, meters, relays

Note: Use exact replacements for critical audio path components.

Schematics

Complete circuit schematics for all sections including power supply, amplifier, preamp, and tuner.

Main Schematic: Overall system schematic showing interconnections

Power Amplifier Schematic: Left and right channel power amplifiers
Preamplifier Schematic: Phono, tone control, and input selection
Power Supply Schematic: Main power supply with regulation
Protection Circuit: Speaker protection and relay drive
FM Tuner Schematic: RF, IF, and multiplex sections
Control Circuit: Switching, indicators, and meter drives

PCB Layouts

Printed circuit board layouts with component placement and trace routing.

Main Amplifier Board: Component side and solder side views
Power Supply Board: Layout with high-current traces
Preamplifier Board: Low-level audio circuit layout
Tuner Assembly: FM/AM tuner module layout
Control Board: Switch and indicator circuit board
Scale Factor: All layouts at 1:1 scale for accurate measurement

Safety Precautions

Critical safety information for technicians working on high-power audio equipment.

HIGH VOLTAGE WARNING: Lethal voltages present in power supply and amplifier sections. Always use isolation transformer during testing. Discharge all capacitors before servicing. Use appropriate personal protective equipment.

Service Notes: This manual is intended for qualified service technicians only. Users should not attempt repairs without proper training and equipment. For service assistance, contact authorized Marantz service centers.