Kenwood A-5J Service Manual

The Kenwood A-5J is a high-performance stereo amplifier featuring advanced audio circuitry, dual power supply system, MM/MC phono equalizer, tone controls, speaker selector, and comprehensive input/output terminals. This service manual provides detailed technical information for service technicians including schematics, adjustment procedures, specifications, and troubleshooting guidelines.

1. Technical Specifications 2. Block Diagram and Circuit Description 3. Disassembly Instructions 4. Adjustment Procedures 5. Schematic Diagrams 6. Parts List 7. PCB Layouts 8. Waveform Charts 9. Troubleshooting Guide 10. Service Notes 11. Safety Precautions

Technical Specifications

Complete electrical and mechanical specifications for the Kenwood A-5J amplifier.

Parameter	Specification
Power Output	80W + 80W (8Ω, 20Hz-20kHz, 0.08% THD)
Total Harmonic Distortion	0.008% (1kHz, 50W, 8Ω)
Frequency Response	5Hz-100kHz (+0, -3dB)
Input Sensitivity	Phono MM: 2.5mV, Phono MC: 0.25mV, Line: 150mV
Signal-to-Noise Ratio	Phono MM: 86dB, Line: 100dB
Tone Control	Bass: ±10dB at 100Hz, Treble: ±10dB at 10kHz
Power Supply	AC 120V/220V/240V, 50/60Hz
Dimensions	430(W) × 150(H) × 385(D) mm
Weight	12.5 kg
Power Consumption	280W (maximum)

Block Diagram and Circuit Description

Detailed explanation of the amplifier's circuit architecture and signal flow.

Power Supply Section: Dual power transformer configuration with separate windings for left/right channels.
Pre-amplifier Stage: High-quality phono equalizer and line amplifier circuits.
Power Amplifier Section: Direct coupling OCL configuration with complementary symmetry output.
Protection Circuitry: DC detection, over-current protection, and thermal shutdown.
Control Circuits: Input selector, tone control, and volume attenuation systems.

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

Disassembly Instructions

Step-by-step guide for accessing internal components.

Remove top cover: Unscrew 6 Phillips screws from top panel.
Remove bottom panel: Turn unit upside down and remove 8 screws.
Front panel removal: Detach knobs and remove 4 screws behind front panel.
PCB access: Remove relevant screws and carefully lift circuit boards.
Heat sink removal: Note thermal compound application for reassembly.

CAUTION! Handle circuit boards by edges only. Use proper ESD protection.

Adjustment Procedures

Factory calibration and alignment procedures.

DC Offset Adjustment: Adjust VR401/VR402 for 0mV ±5mV at speaker terminals.
Bias Current Adjustment: Set VR403/VR404 for 20mA across emitter resistors.
Phono Equalizer: Verify RIAA curve accuracy using test equipment.
Protection Circuit: Test DC detection and relay operation.
Meter Calibration: Adjust for accurate power level indication.

Schematic Diagrams

Complete circuit schematics for all sections.

Main Amplifier: Power amplifier, driver stage, and protection circuits.

Pre-amplifier: Phono equalizer, tone control, and input selector circuits.

Power Supply: Main transformer, rectification, and regulation circuits.

Control Circuits: Input switching, relay control, and indicator circuits.

Parts List

Comprehensive list of components with manufacturer part numbers.

Reference	Description	Part Number
Q101-Q104	Transistor 2SC2240	KSC1845
Q201-Q204	Transistor 2SA970	KSA992
Q401-Q404	Output Transistor 2SC3281/2SA1302	MJ21193/MJ21194
IC101	Operational Amplifier NJM4558	NJM4558
C101-C104	Capacitor 100μF/16V	ECE-A1CN101
R101-R104	Resistor 10kΩ 1/4W	CF1/4C103J
T401	Power Transformer	TPC-301

PCB Layouts

Printed circuit board patterns and component placement guides.

Main Amplifier Board: Component side and solder side patterns.
Pre-amplifier Board: Detailed component layout and trace routing.
Power Supply Board: High-current traces and component placement.
Control Board: Switch and indicator circuit layouts.

Tip: Use exact replacement components to maintain circuit integrity.

Waveform Charts

Reference waveforms at key test points under various operating conditions.

Square wave response: 1kHz and 10kHz square wave outputs.
Frequency response: 20Hz-20kHz sweep characteristics.
Distortion analysis: THD vs frequency and power output.
Transient response: Pulse and step function analysis.
Noise floor: Residual noise spectrum analysis.

WARNING! Use proper test equipment and follow safety procedures.

Troubleshooting Guide

Systematic approach to diagnosing and repairing common issues.

Symptom	Possible Cause	Corrective Action
No power	Fuse blown, power switch, transformer	Check fuse F401/F402; test power switch; verify transformer primary.
No sound output	Protection relay, output transistors	Check relay operation; test output transistors Q401-Q404.
Distorted sound	Bias current, DC offset, capacitors	Adjust bias and DC offset; check electrolytic capacitors.
Hum or noise	Grounding, capacitors, transistors	Verify ground connections; replace filter capacitors; check noisy transistors.
One channel dead	Channel-specific components	Compare working/non-working channels; check IC101, Q101-Q104.

Service Notes

Important technical notes and service tips from Kenwood engineers.

Use only specified replacement parts. Maintain original circuit characteristics. Follow adjustment procedures precisely. Document all modifications. Keep work area clean and organized.

Safety Precautions

Essential safety guidelines for service personnel.

DANGER! Lethal voltages present. Always disconnect power before servicing. Use isolation transformer when testing live circuits. Discharge large capacitors before handling. Follow proper grounding procedures. Use appropriate personal protective equipment.

Service Support: Kenwood Technical Support: 1-800-536-9663; www.kenwood.com