Marantz 2500 Service Manual

The Marantz 2500 is a high-power stereo receiver from the classic era, featuring 250 watts per channel RMS power output, advanced tuning capabilities, comprehensive input/output options, and the distinctive Marantz blue dial display. This service manual covers technical specifications, circuit diagrams, alignment procedures, troubleshooting guides, and maintenance instructions for qualified service technicians.

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

Technical Specifications

Complete electrical and mechanical specifications for the Marantz 2500 stereo receiver.

Parameter	Specification
Power Output	250 watts per channel RMS (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
Tuning Range	FM: 87.5-108MHz; AM: 530-1620kHz
Power Requirements	120V AC, 60Hz, 750W max
Dimensions	21.5" W × 7.5" H × 18.5" D
Weight	68 lbs (30.8 kg)

Block Diagrams

System block diagrams showing signal flow and power distribution.

Main System Block Diagram: Overview of all major sections
Preamplifier Section: Phono, aux, tape monitor circuits
Power Amplifier Section: Output stages and protection circuits
Tuner Section: FM and AM receiver blocks
Power Supply Section: Voltage regulation and distribution

WARNING! High voltage present in power supply section. Exercise extreme caution when servicing.

Circuit Descriptions

Detailed circuit analysis and component functions.

Power Amplifier Circuit: Complementary symmetry output stages
Preamplifier Circuit: Low-noise phono equalization
Tuner Circuits: FM multiplex and AM detection
Protection Circuits: DC detection and thermal protection
Power Supply: Dual secondary transformer with regulated supplies

CAUTION! Always discharge large capacitors before servicing.

Alignment Procedures

FM Tuner Alignment: IF stages, discriminator, and oscillator
AM Tuner Alignment: RF and IF transformer adjustments
Dolby Circuit Alignment: Level and frequency response
Power Amplifier Bias: DC offset and idle current adjustment
Meter Calibration: Power output meter alignment
Required Test Equipment: Audio generator, oscilloscope, VTVM, distortion analyzer
Alignment Tools: Plastic alignment tools for core adjustments

Disassembly Instructions

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

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

Power off and unplug unit before disassembly
Remove rear panel screws and top cover
Detach front panel knobs and mounting hardware
Remove main amplifier heat sink assembly
Access individual circuit boards for service

Tip: Document wire positions and take photos during disassembly.

Parts List

Complete component listing with manufacturer part numbers.

Component	Part Number	Description
Output Transistors	2SC2581/2SA1106	Complementary power transistors
Main Filter Caps	15,000μF 80V	Dual main power supply capacitors
Driver Transistors	2SC1708/2SA968	Driver stage complementary pair
Fuse	8A 250V	Main AC line fuse
Meter Lamps	8V 300mA	Blue filter illumination lamps

PCB Layouts

Printed circuit board layouts and component placement diagrams.

Main Amplifier Board: Power output and driver stages
Preamplifier Board: Input selection and tone controls
Power Supply Board: Rectification and regulation
Tuner Board: FM/AM receiver circuits
Protection Board: Speaker protection and relay control

WARNING! Observe proper grounding techniques when working on PCBs.

Voltage Measurements

Reference voltage measurements at key test points.

Test Point	Expected Voltage	Tolerance
Main B+	±65V DC	±5%
Driver Stage	±55V DC	±5%
Preamplifier	±15V DC	±10%
Tuner Section	+12V DC	±5%
Protection Circuit	+24V DC	±10%

Troubleshooting Guide

Common problems and diagnostic procedures.

Symptom	Possible Cause	Corrective Action
No power	Blown fuse, power switch	Check main fuse; test power switch continuity
Distorted audio	Bias adjustment, output transistors	Adjust bias current; test output devices
No FM reception	Tuner alignment, MPX circuit	Align FM stages; check multiplex decoder
Protection relay trips	DC offset, short circuit	Measure DC offset; check speaker connections
Meter not working	Meter movement, driver circuit	Test meter coil; check meter driver transistors

Reset: Check all adjustments after component replacement.

Safety Precautions

Essential safety procedures for service technicians.

Use isolation transformer; discharge capacitors; wear safety glasses; work in well-ventilated area.

CAUTION! Lethal voltages present. Only qualified technicians should perform service.

Service Notes

Additional technical information and service tips.

Factory service bulletins; common failure points; recommended upgrades; vintage component sourcing. For technical support contact authorized Marantz service centers. Original documentation copyright Marantz Company.