KR 5600 Kenwood Bias Service Manual

The Kenwood KR-5600 is a stereo receiver featuring 60 watts per channel RMS power output, quartz PLL synthesized tuning, FET front end, and advanced bias adjustment capabilities. This service manual covers technical specifications, bias adjustment procedures, circuit diagrams, troubleshooting, and maintenance guidelines for proper calibration and optimal performance of the KR-5600 receiver.

1. Technical Specifications 2. Bias Adjustment Procedures 3. Circuit Diagrams 4. Test Points and Measurements 5. Power Supply Section 6. Amplifier Section 7. Tuner Section 8. Safety Precautions 9. Troubleshooting Guide 10. Parts List 11. Service Notes

Technical Specifications

Complete technical specifications for the Kenwood KR-5600 stereo receiver.

Parameter	Specification
Power Output	60W per channel RMS (8Ω, 20Hz-20kHz)
Total Harmonic Distortion	0.02% (rated power)
Frequency Response	10Hz-50kHz (+0, -1dB)
Input Sensitivity	Phono: 2.5mV; Aux: 150mV
Signal-to-Noise Ratio	Phono: 76dB; Aux: 95dB
Tuning Range	FM: 87.5-108MHz; AM: 530-1620kHz
Bias Current	20-25mA (adjustable)
Power Consumption	280W (max)
Dimensions	480W × 150H × 355D mm
Weight	12.5 kg

Bias Adjustment Procedures

Proper bias adjustment is critical for optimal performance and longevity.

Warm up unit: Power on receiver and allow 30 minutes for thermal stabilization.
Connect test equipment: Attach digital multimeter to bias test points.
Locate bias adjustment: Identify VR601 and VR602 on main amplifier board.
Adjust bias current: Set to 22mA ±2mA using specified adjustment points.
Verify stability: Monitor for 5 minutes to ensure stable reading.

WARNING! Ensure proper isolation and use appropriate test equipment. High voltages present.

Circuit Diagrams

Complete schematic diagrams for all sections of the KR-5600.

Main Amplifier Circuit: Complete power amplifier schematic with component values.
Power Supply Circuit: Transformer, rectifiers, and regulation circuits.
Tuner Section: FM/AM tuner circuits with alignment points.
Control Circuits: Tone control, input selection, and protection circuits.
Protection Circuit: Speaker protection and thermal shutdown.
Display Circuit: Signal strength and tuning indicator circuits.

Test Points and Measurements

Key test points for service and alignment procedures.

Test Point	Location	Normal Value
TP1	Main board near Q1	+48V DC
TP2	Power supply output	+35V DC
TP3	Bias test point L	22mA ±2mA
TP4	Bias test point R	22mA ±2mA
TP5	Center voltage	0V ±50mV
TP6	Protection circuit	0.6V DC

Power Supply Section

Detailed power supply specifications and service information.

Transformer: Primary 120V AC, secondary 35V-0-35V AC.
Rectification: Full-wave bridge rectifier D601-D604.
Filtering: Main capacitors C601, C602 (6800μF/50V).
Regulation: Transistor regulators for low-voltage supplies.
Protection: Fuse F601 (4A) and thermal protection.

CAUTION! High voltage capacitors retain charge after power off.

Amplifier Section

Power amplifier circuit details and service procedures.

Output Stage: Complementary symmetry push-pull configuration with 2SC2581/2SA1106 output transistors.

Driver Stage: 2SC2275/2SA985 driver transistors with thermal compensation.

Bias Circuit: Temperature-compensated bias network with adjustment potentiometers VR601 (left) and VR602 (right).

Protection: DC detection and overcurrent protection circuits.

Tuner Section

FM/AM tuner alignment and service information.

FM Front End: FET RF amplifier with varactor tuning.
IF Stages: Ceramic filters and IC-based IF amplification.
MPX Decoder: PLL stereo decoder circuit.
AM Tuner: Ferrite antenna and IC-based AM detection.
Alignment: Required test equipment and procedure steps.

Tip: Use non-metallic alignment tools for FM front end adjustments.

Safety Precautions

Essential safety procedures for service technicians.

Always disconnect AC power before servicing.
Use isolation transformer when testing live circuits.
Discharge high-voltage capacitors before handling.
Verify proper grounding of test equipment.
Wear appropriate personal protective equipment.

WARNING! Lethal voltages present. Qualified technicians only.

Troubleshooting Guide

Common problems and solutions for the KR-5600.

Symptom	Possible Cause	Corrective Action
No power	Blown fuse, power switch	Check F601, power switch, transformer primary
Distorted audio	Bias misadjustment, output transistors	Adjust bias current, check output transistors
Protection circuit engaged	DC offset, short circuit	Check output DC voltage, speaker connections
No FM reception	Tuner section, antenna	Verify antenna connection, check tuner power
Intermittent operation	Cold solder joints, connectors	Inspect solder joints, clean connectors

Parts List

Critical replacement parts and components.

Output Transistors: 2SC2581 / 2SA1106 (matched pairs)
Driver Transistors: 2SC2275 / 2SA985
Power Supply Diodes: 1S1886 or equivalent
Main Filter Capacitors: 6800μF/50V
Bias Adjustment Pots: VR601, VR602 (500Ω)
Main Fuse: F601 4A slow-blow
IC Components: HA12016, μPC1237, LA1260

Service Notes

Important service information and technical notes.

Bias adjustment must be performed after replacing output transistors. Always use matched pairs for replacement. Thermal compound application is critical for proper heat transfer. Allow adequate warm-up time before measurements. Document all adjustments for future reference.

Service Support: Kenwood authorized service centers only. Original parts recommended for optimal performance.

Revision History: Initial release 1978. Service bulletin updates available through Kenwood technical support.