Kenwood KR 4070 Service Manual

The Kenwood KR 4070 is a high-performance stereo receiver featuring AM/FM tuner, 45 watts per channel RMS power output, phono input for turntables, tape monitoring, loudness control, and comprehensive tone controls. This service manual provides detailed technical information for service technicians, including schematics, alignment procedures, parts list, and troubleshooting guidelines for proper maintenance and repair.

1. Technical Specifications 2. Block Diagram 3. Circuit Description 4. Alignment Procedures 5. Disassembly Instructions 6. Parts List 7. Schematic Diagrams 8. PCB Layout 9. Troubleshooting Guide 10. Service Precautions 11. Warranty Information

Technical Specifications

Complete technical specifications for the Kenwood KR 4070 stereo receiver.

Parameter	Specification
Power Output	45W per channel RMS (8Ω, 20Hz-20kHz)
Total Harmonic Distortion	0.08% (at rated output)
Frequency Response	10Hz-50kHz (+1, -3dB)
Input Sensitivity	Phono: 2.5mV, AUX: 150mV
Signal-to-Noise Ratio	Phono: 70dB, AUX: 90dB
Tuner Section	AM/FM with multiplex stereo
FM Sensitivity	1.9μV (IHF)
Capture Ratio	1.5dB
Selectivity	70dB
Dimensions	440 x 150 x 360mm (W x H x D)
Weight	9.5kg

Block Diagram

System block diagram showing signal flow and major components.

FM Tuner Section: RF amplifier, mixer, IF stages, detector
AM Tuner Section: RF stage, converter, IF amplifier, detector
Preamplifier: Phono equalizer, tone controls, volume/balance
Power Amplifier: Driver stage, output transistors, protection circuit
Power Supply: Transformer, rectifiers, regulators

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

Circuit Description

Detailed circuit analysis of major sections.

FM Front End: 3-gang variable capacitor, RF amplifier, local oscillator
IF Stages: 3-stage ceramic filter, limiter, ratio detector
Phono Equalizer: RIAA equalization with low-noise transistors
Tone Control: Bass and treble controls with center detent
Power Amplifier: Complementary symmetry output, current mirror
Protection Circuit: DC detection, overcurrent protection

CAUTION! Use proper grounding techniques when testing circuits.

Alignment Procedures

FM IF Alignment: Adjust ceramic filters for maximum output at 10.7MHz
FM Detector Alignment: Set detector transformer for minimum distortion
AM Alignment: Adjust oscillator and antenna trimmers for tracking
Stereo Decoder: Adjust 19kHz and 38kHz for proper separation
Power Amplifier: Set bias current to 20mA per channel
DC Offset: Adjust for 0V DC at speaker terminals
Test Equipment Required: Signal generator, oscilloscope, VTVM, distortion analyzer

Disassembly Instructions

Step-by-step disassembly procedure for service access.

Front Panel Removal: Remove knobs, unscrew front panel screws, disconnect wiring harnesses.

Top Cover Removal: Remove rear screws, slide cover backward.

Bottom Cover Removal: Remove screws from underside.

Main Board Access: Remove shields, disconnect inter-board cables.

Tuner Section: Special care required for alignment components.

Parts List

Complete list of components with part numbers and specifications.

Part Number	Description	Specification
2SC1345	Small signal transistor	NPN, 50V, 100mA
2SA726	Small signal transistor	PNP, 50V, 100mA
2SC1383	Driver transistor	NPN, 80V, 1A
2SA684	Driver transistor	PNP, 80V, 1A
2SC1116	Output transistor	NPN, 120V, 8A
2SA747	Output transistor	PNP, 120V, 8A
LA1230	FM IF IC	10.7MHz amplifier/detector
HA1156W	Stereo decoder IC	PLL multiplex decoder

Schematic Diagrams

Complete schematic diagrams for all sections.

Main amplifier schematic with voltage measurements
Preamplifier and tone control schematic
FM tuner schematic with alignment points
AM tuner schematic
Power supply schematic with test points
Protection circuit schematic

Tip: Refer to voltage chart for proper operating conditions.

PCB Layout

Printed circuit board layouts and component locations.

Main amplifier board component side
Main amplifier board solder side
Tuner board component side
Tuner board solder side
Power supply board layout
Front panel board layout

WARNING! Observe component orientation when replacing parts.

Troubleshooting Guide

Systematic troubleshooting procedures for common problems.

Symptom	Possible Cause	Corrective Action
No power	Fuse, power switch, transformer	Check fuse F801 (4A), measure transformer primary voltage
No audio output	Protection circuit, amplifier stage	Check protection relay, measure output transistor voltages
Distorted sound	Bias current, output transistors	Adjust VR701/VR702 bias, check output transistors
No FM reception	Tuner section, power supply	Check tuner supply voltages, local oscillator operation
Poor FM stereo	Decoder alignment, signal strength	Adjust stereo decoder VR301 for maximum separation
Hum in audio	Grounding, filter capacitors	Check ground connections, replace filter capacitors C801/C802

Service Precautions

Important safety precautions for service technicians.

Use isolation transformer when testing. Discharge large capacitors before servicing. Use correct replacement parts. Observe static precautions for MOS devices. Maintain original lead lengths in RF circuits.

CAUTION! Lethal voltages present. Use properly insulated tools.

Warranty Information

Kenwood warranty policy and service center information.

Original warranty: 2 years parts and labor. Authorized service centers only. Keep original sales receipt. Warranty void if seals broken by unauthorized personnel. For service, contact authorized Kenwood service center or Kenwood Corporation, Japan.