Kenwood KA 907 Service Manual

The Kenwood KA 907 is a high-performance stereo integrated amplifier featuring dual mono construction, high current capability, 150W RMS per channel into 8 ohms, MM/MC phono inputs, multiple line inputs, tape monitoring, tone controls, loudness compensation, and direct coupling circuitry. Below are key sections for technical specifications, circuit description, adjustment procedures, disassembly instructions, troubleshooting, and parts list.

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

Technical Specifications

Complete electrical and mechanical specifications for the Kenwood KA 907 amplifier.

Parameter	Specification
Power Output	150W RMS per channel (8Ω, 20Hz-20kHz)
Total Harmonic Distortion	<0.005% (rated power)
Frequency Response	5Hz-100kHz (+0, -3dB)
Input Sensitivity	Phono MC: 0.15mV; Phono MM: 2.5mV; Line: 150mV
Signal-to-Noise Ratio	Phono MC: 74dB; Phono MM: 86dB; Line: 106dB
Tone Controls	Bass: ±10dB at 100Hz; Treble: ±10dB at 10kHz
Power Supply	AC 120V/220V/240V, 50/60Hz
Dimensions	440(W) x 150(H) x 390(D) mm
Weight	18.5 kg
Power Consumption	500W (maximum)

Block Diagram & Circuit Description

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

Power Supply Section: Dual mono configuration with separate transformers for left and right channels
Pre-amplifier Stage: Discrete component design with low-noise transistors
Phono Equalizer: Switchable MM/MC with RIAA equalization accuracy within ±0.2dB
Power Amplifier Section: Complementary symmetry push-pull configuration
Protection Circuit: DC detection, overcurrent protection, and thermal shutdown

WARNING! High voltages present in power supply section. Discharge capacitors before servicing.

Adjustment Procedures

Step-by-step instructions for calibrating and adjusting the amplifier.

DC Offset Adjustment: Adjust VR101/VR102 for 0mV ±5mV at speaker terminals
Bias Current Adjustment: Set VR103/VR104 for 20mA across emitter resistors
Phono Gain Adjustment: Calibrate MC/MM input levels using test records
Meter Calibration: Adjust power meter sensitivity for accurate readings

CAUTION! Use insulated tools and follow electrostatic discharge precautions.

Disassembly Instructions

Top Cover Removal: Remove 6 screws from rear panel and 2 from sides
Front Panel Removal: Detach knobs and remove 4 mounting screws
Main Board Access: Remove shield covers and disconnect wiring harnesses
Power Supply Removal: Discharge capacitors and remove transformer mounting bolts
Heat Sink Removal: Remove output transistors and thermal compound carefully

Schematic Diagrams

Complete circuit schematics for all sections of the amplifier.

Main Amplifier Circuit (Left/Right Channels)
Power Supply and Protection Circuit
Pre-amplifier and Tone Control Circuit
Phono Equalizer Circuit (MM/MC)
Input Selector and Tape Monitor Circuit
Front Panel Control Circuit

Note: All schematics include component values, test points, and voltage readings.

PCB Layouts

Printed circuit board layouts with component placement and trace routing.

Board	Dimensions	Components
Main Amplifier Board	320mm x 180mm	Q101-Q110, IC101-IC102
Power Supply Board	150mm x 120mm	D101-D108, C101-C108
Pre-amplifier Board	200mm x 100mm	Q201-Q208, IC201
Phono Board	120mm x 80mm	Q301-Q304, R301-R312
Control Board	180mm x 60mm	SW101-SW105, VR101-VR104

Parts List

Complete listing of all components with manufacturer part numbers.

Transistors: 2SC2240, 2SA970, 2SC2705, 2SA1145, 2SC3281, 2SA1302
Integrated Circuits: NJM4558, TA7317P, μPC1237
Capacitors: 10,000μF/63V (main filter), 470μF/50V (audio), 100pF ceramic
Resistors: Metal film 1/4W and 1/2W, power resistors 5W
Potentiometers: Volume, balance, bass, treble (ALPS type)
Switches: Rotary selector, push button, toggle

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
No power	Fuse blown, power switch faulty	Check F101-F102 (5A); replace power switch
Distortion in one channel	Output transistors, bias current	Test Q107-Q110; adjust bias current
Hum or noise	Grounding issues, capacitor failure	Check ground connections; replace C101-C108
Protection circuit engaged	DC offset, overcurrent	Measure DC offset; check output stage
Phono input not working	Selector switch, phono board	Clean selector contacts; test phono stage

Service Notes

Important technical notes and modifications for service technicians.

Thermal Management: Ensure proper heat sink compound application
Component Substitutions: Approved equivalent parts for obsolete components
Alignment Procedures: Required test equipment and setup
Common Failures: Typical component failures and replacement intervals
Factory Updates: Service bulletins and circuit modifications

WARNING! Always use original or approved replacement parts.

Safety Precautions

Essential safety procedures for servicing high-power audio equipment.

Always disconnect AC power before servicing
Discharge large capacitors before working on power supply
Use isolation transformer when testing live circuits
Wear safety glasses when replacing components
Follow electrostatic discharge (ESD) precautions
Verify correct reassembly before applying power

CAUTION! Lethal voltages present. Qualified technicians only.