Marantz 5025B Service Manual

The Marantz 5025B is a professional audio amplifier/receiver featuring high-fidelity sound reproduction, multiple input/output connections, advanced tone controls, and robust construction for reliable performance. This service manual provides comprehensive technical information for installation, operation, maintenance, and troubleshooting of the unit.

1. Technical Specifications 2. Installation Guidelines 3. Front Panel Controls 4. Rear Panel Connections 5. Operation Procedures 6. Circuit Description 7. Alignment Procedures 8. Maintenance & Service 9. Parts List 10. Schematic Diagrams 11. Troubleshooting Guide

Technical Specifications

Complete technical specifications for the Marantz 5025B audio amplifier/receiver.

Parameter	Specification
Power Output	50W RMS per channel (8Ω)
Frequency Response	20Hz - 20kHz ±1dB
Total Harmonic Distortion	<0.05% at rated output
Signal-to-Noise Ratio	>85dB
Input Sensitivity	150mV (AUX), 2.5mV (Phono)
Input Impedance	47kΩ (AUX), 47kΩ/100pF (Phono)
Tone Controls	Bass ±10dB, Treble ±10dB
Power Requirements	120V AC, 60Hz, 200W
Dimensions	17" W × 4.5" H × 12" D
Weight	15.4 lbs (7 kg)

Installation Guidelines

Proper installation procedures for optimal performance and safety.

Choose a well-ventilated location with adequate air circulation.
Connect speakers using appropriate gauge speaker wire.
Connect audio sources to corresponding input jacks.
Connect AC power cord to grounded outlet.
Ensure all connections are secure before powering on.

WARNING! Ensure proper ventilation to prevent overheating. Do not block ventilation openings.

Front Panel Controls

Description and function of all front panel controls and indicators.

Control/Indicator	Function
POWER Switch	Main power on/off control
VOLUME Knob	Master volume control
BASS Control	Adjusts low frequency response
TREBLE Control	Adjusts high frequency response
BALANCE Control	Adjusts left/right channel balance
INPUT Selector	Selects audio source (Phono, AUX, Tuner)
Power Indicator	Illuminates when unit is powered on
Protection LED	Indicates protection circuit activation

Rear Panel Connections

Complete overview of all rear panel input/output connections.

SPEAKER TERMINALS: Spring-clip terminals for speaker connections
PHONO INPUT: RCA jacks for turntable connection
AUX INPUT: RCA jacks for auxiliary audio sources
TUNER INPUT: RCA jacks for tuner connection
TAPE IN/OUT: RCA jacks for tape deck connection
AC POWER CORD: Detachable power cord
FUSE HOLDER: Contains main power fuse

Operation Procedures

Standard operating procedures for normal use.

Turn volume control to minimum position before powering on.
Press POWER switch to turn unit on.
Select desired input source using INPUT selector.
Adjust volume to desired listening level.
Use tone controls to adjust bass and treble response.
Use balance control to adjust left/right channel balance.
Turn volume to minimum before powering off.

CAUTION! Avoid operating at maximum volume for extended periods to prevent damage.

Circuit Description

Detailed description of major circuit blocks and their functions.

Power Supply: Transformer-rectifier circuit providing ±35V DC rails
Preamplifier Stage: Low-noise amplification with RIAA equalization
Tone Control Circuit: Active bass and treble control network
Power Amplifier: Complementary symmetry output stage
Protection Circuit: DC detection and thermal protection
Selector Switches: Rotary switches for input selection

Alignment Procedures

Factory alignment and adjustment procedures for service technicians.

DC Offset Adjustment: Adjust VR501 for 0V DC at speaker terminals
Bias Current Adjustment: Adjust VR502 for 20mA idle current
Phono Equalization: Verify RIAA response using test equipment
Tone Control Center: Adjust for flat response at center detent
Input Sensitivity: Verify specified input sensitivity levels

NOTE: These procedures require specialized test equipment and technical expertise.

Maintenance & Service

Routine maintenance and service procedures for long-term reliability.

Clean controls and switches with contact cleaner annually
Check and tighten all internal connections during service
Inspect power supply capacitors for signs of leakage
Verify proper heat sink contact for output transistors
Clean ventilation openings to ensure proper cooling

WARNING! Disconnect AC power before performing any internal service.

Parts List

Complete list of replacement parts with manufacturer part numbers.

Part Number	Description	Qty
2SC2344	Output Transistor	2
2SA1011	Output Transistor	2
TA7136P	Preamplifier IC	1
1S1588	Protection Diode	4
3300μF/50V	Main Filter Capacitor	2
T3.15A	Line Fuse	1
VR501	DC Offset Adjust	1
VR502	Bias Adjust	1

Schematic Diagrams

Reference to included schematic diagrams for detailed circuit analysis.

Main Amplifier Circuit (Page 12)
Preamplifier and Tone Control (Page 13)
Power Supply Circuit (Page 14)
Protection Circuit (Page 15)
Selector Switch Matrix (Page 16)
PCB Layout Diagrams (Pages 17-18)

NOTE: Full schematic diagrams are included in the complete PDF manual.

Troubleshooting Guide

Systematic troubleshooting procedures for common problems.

Symptom	Possible Cause	Corrective Action
No power	Blown fuse, power cord	Check/replace fuse; verify power cord connection
No sound	Protection circuit, speakers	Check protection LED; verify speaker connections
Distorted sound	Output transistors, bias	Check output devices; adjust bias current
Hum/buzz	Grounding, capacitors	Check ground connections; test filter capacitors
Intermittent operation	Cold solder joints, switches	Inspect PCB for cold joints; clean switches
One channel dead	Amplifier stage, selector	Check amplifier components; clean selector switch

Service Contact: Authorized Marantz service centers only.