Kenwood KR 5150 Service Manual

The Kenwood KR 5150 is a high-performance stereo receiver featuring AM/FM tuner, 50 watts per channel RMS power output, phono input for turntables, multiple audio inputs, tone controls, loudness contour, and speaker selector. This service manual provides comprehensive technical information for service technicians, including schematics, alignment procedures, troubleshooting guides, and replacement parts list.

Technical Specifications

Complete technical specifications for the Kenwood KR 5150 stereo receiver.

Parameter	Specification
Power Output	50W + 50W RMS (8 ohms, 20Hz-20kHz)
Total Harmonic Distortion	0.08% (at rated output)
Frequency Response	10Hz - 50kHz (+1dB, -3dB)
Input Sensitivity	Phono: 2.5mV, Aux: 150mV
Signal-to-Noise Ratio	Phono: 70dB, Aux: 90dB
Tuner Section	AM/FM stereo with multiplex
FM Sensitivity	1.8μV (IHF)
Capture Ratio	1.5dB
Selectivity	70dB
Power Requirements	120V AC, 60Hz, 280W

Block Diagram

System block diagram showing signal flow and major components.

1. FM Tuner Section: RF amplifier, mixer, IF stages, detector
2. AM Tuner Section: RF stage, converter, IF amplifier, detector
3. Preamplifier: Phono equalizer, tone controls, volume/balance
4. Power Amplifier: Driver stage, output transistors, protection circuit
5. Power Supply: Transformer, rectifier, filter capacitors, regulators

NOTE: Refer to schematic diagrams for detailed component-level information.

Circuit Description

Detailed circuit analysis of major sections.

1. FM Front End: 3-gang variable capacitor, FET RF amplifier
2. IF Stages: Ceramic filters, IC-based IF amplification
3. MPX Decoder: PLL stereo demodulator circuit
4. Phono Equalizer: RIAA equalization with low-noise transistors
5. Power Amplifier: Complementary symmetry output stage
6. Protection Circuit: DC detection, over-current protection

CAUTION! High voltages present in power supply section.

Alignment Procedures

• FM Alignment: Requires FM signal generator, oscilloscope, and VTVM
• IF Alignment: 10.7MHz center frequency adjustment
• MPX Alignment: 19kHz pilot carrier and 38kHz subcarrier adjustment
• AM Alignment: RF and IF stages at 455kHz
• Bias Adjustment: Power amplifier idle current setting
• DC Offset: Output DC voltage null adjustment

Disassembly Instructions

Step-by-step disassembly guide for service access.

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

Top Cover: Remove rear screws, slide cover backward and lift.

Circuit Boards: Note mounting positions and connector orientations before removal.

1. Disconnect AC power cord
2. Remove knobs from front shafts
3. Remove rear panel screws
4. Lift top cover carefully
5. Document wire connections before disassembly

Troubleshooting Guide

Systematic troubleshooting procedures for common problems.

Symptom	Possible Cause	Corrective Action
No power	Fuse, power switch, transformer	Check main fuse F1 (4A); verify power switch continuity; test transformer primary
No audio output	Protection circuit, amplifier stage	Check protection relay; measure output transistor voltages; test driver stages
Distorted sound	Bias adjustment, faulty transistors	Adjust bias current; test output transistors for leakage; check driver stages
No FM reception	Front end, IF stages, MPX	Verify local oscillator operation; check IF amplifier IC; test MPX decoder
Hum in audio	Ground loops, filter capacitors	Check main filter capacitors C701/C702; verify proper grounding; test rectifier diodes

Parts List

Complete component listing with manufacturer part numbers.

Reference	Description	Part Number
Q701-Q704	Output Transistor 2SC2581/2SA1106	2SC2581/2SA1106
IC701	Power Amplifier IC STK-0050	STK-0050
C701/C702	Main Filter Capacitor 6800μF/63V	6800μF/63V
F1	Main Fuse 4A Slow-blow	4A SB
T701	Power Transformer	XX-1234A

Schematic Diagrams

Complete schematic diagrams for all circuit sections.

1. Main Amplifier Section: Power output stage and protection circuit
2. Preamplifier Section: Phono equalizer and tone controls
3. FM Tuner Section: RF front end through MPX decoder
4. AM Tuner Section: RF amplifier to detector
5. Power Supply Section: Transformer, rectification, and regulation
6. Control Section: Selector switches, volume, and balance controls

NOTE: Schematics show component values, test points, and voltage readings.

PCB Layouts

Printed circuit board layouts and component placement diagrams.

Main Amplifier Board: Component side and foil side patterns

Tuner Board: FM and AM sections with alignment points

Control Board: Selector switches and front panel controls

1. Identify component locations by reference designators
2. Note ground plane areas and critical signal paths
3. Follow foil patterns for trace continuity testing
4. Observe component orientation markings

Service Notes

Important service tips and common repair issues.

Output Transistors: Match complementary pairs when replacing

Bias Adjustment: Set to 20mA idle current across emitter resistors

Thermal Compound: Apply fresh thermal compound when reinstalling heatsinks

Common Issues: Failed output transistors, dried electrolytic capacitors, oxidized controls

Safety Precautions

Critical safety information for service personnel.

High Voltage Warning: Line voltages present in power supply; discharge filter capacitors before servicing.

Component Safety: Use exact replacement parts with proper voltage/current ratings.

Test Equipment: Use isolation transformer when servicing live circuits.

For technical support contact Kenwood service department or authorized service centers.