Kenwood 440S Service Manual

The Kenwood 440S is a professional-grade stereo receiver featuring advanced audio processing, multiple input/output options, and robust construction for reliable performance. This service manual covers technical specifications, installation procedures, operational guidelines, maintenance instructions, and troubleshooting procedures for qualified service technicians.

Technical Specifications

Key technical parameters and performance characteristics of the Kenwood 440S stereo receiver.

Parameter	Specification
Power Output	100W RMS per channel (8Ω)
Frequency Response	20Hz - 20kHz (±0.5dB)
Total Harmonic Distortion	<0.05% at rated power
Signal-to-Noise Ratio	>95dB (line input)
Input Sensitivity	150mV (line), 2.5mV (phono)
Input Impedance	47kΩ (line), 50kΩ (phono)
Power Requirements	120V AC, 60Hz, 350W max
Dimensions	17.1" W × 6.3" H × 15.7" D
Weight	28.6 lbs (13 kg)
Operating Temperature	41°F to 95°F (5°C to 35°C)

Installation Procedures

Proper installation guidelines for optimal performance and safety.

1. Unpack and inspect unit for shipping damage before installation.
2. Place on stable, level surface with adequate ventilation (minimum 4" clearance on all sides).
3. Connect speakers using appropriate gauge speaker wire (16 AWG minimum).
4. Connect audio sources (CD player, turntable, tape deck) to corresponding inputs.
5. Connect AC power cord to properly grounded outlet.

WARNING! Ensure proper ventilation to prevent overheating. Do not block ventilation openings.

Operational Controls

Front panel controls and their functions for normal operation.

Front Panel: POWER switch, INPUT SELECTOR (PHONO, CD, TUNER, AUX), VOLUME control, BASS/TREBLE controls, BALANCE control, LOUDNESS switch, HEADPHONE jack.

Rear Panel: SPEAKER terminals (A/B), PHONO inputs, LINE inputs, TAPE IN/OUT, PRE-OUT/MAIN-IN jacks, AC power inlet, FUSE holder.

Display: Power indicator, protection indicator, signal strength meter (tuner mode).

Circuit Diagrams

Complete schematic diagrams for all circuit sections.

• Power Supply Section: Transformer, rectifiers, regulators, protection circuits.
• Amplifier Section: Pre-amplifier, power amplifier, protection circuitry.
• Control Section: Input selection, tone control, volume control circuits.
• Tuner Section: RF amplifier, mixer, IF stages, detector circuits.
• Protection Circuits: DC detection, thermal protection, overload protection.

Note: All diagrams include component values and test point locations.

Alignment Procedures

Factory alignment procedures for maintaining optimal performance.

1. FM Tuner Alignment: Adjust RF stages, oscillator, IF transformers for maximum sensitivity and minimum distortion.
2. AM Tuner Alignment: Adjust antenna trimmer, oscillator coil, IF transformers.
3. Phono Equalization: Verify RIAA equalization curve accuracy.
4. Bias Current Adjustment: Set output stage bias current to specified value.
5. DC Offset Adjustment: Null DC offset at speaker outputs.

CAUTION! Use proper test equipment and follow procedures exactly.

Component Layout

Physical location of major components on chassis and PC boards.

Component	Location	Board Reference
Power Transformer	Left rear chassis	N/A
Main Amplifier IC	Center heatsink	IC701, IC702
Power Supply Regulators	Right side board	Q901-Q904
Tuner Module	Front left section	TU-101
Control Microprocessor	Front panel board	IC101
Protection Relay	Near speaker terminals	RY701

Test Points & Measurements

Designated test points and expected voltage/current measurements.

1. TP1: +48V DC supply - should measure +46V to +50V
2. TP2: +15V DC supply - should measure +14.5V to +15.5V
3. TP3: -15V DC supply - should measure -14.5V to -15.5V
4. TP4: Speaker output DC offset - should be < ±50mV
5. TP5: Bias current test point - adjust for 20mA ±2mA
6. TP6: Protection circuit trigger - normally 0V, >2V indicates fault

Measurement Conditions: No signal input, volume minimum, all controls centered.

Maintenance Schedule

Recommended maintenance intervals and procedures.

• Every 6 months: Clean controls with contact cleaner, check ventilation
• Annually: Verify DC offset and bias current settings
• Every 2 years: Clean internal dust, check electrolytic capacitors
• Every 5 years: Replace protection relay contacts if necessary
• As needed: Replace fuses with exact same type and rating

WARNING! Disconnect AC power before performing any maintenance.

Safety Precautions

Critical safety information for service personnel.

1. Always disconnect AC power before servicing.
2. Use isolation transformer when servicing live circuits.
3. Discharge large capacitors before handling.
4. Replace fuses only with specified type and rating.
5. Use proper grounding techniques to prevent static damage.

DANGER! Lethal voltages present even when unit is switched off. Exercise extreme caution.

Parts List

Complete listing of replacement parts with manufacturer part numbers.

Part Number	Description	Qty
X40-1230-01	Power Transformer	1
X40-1240-11	Main Amplifier IC (STK-4152)	2
X40-1250-05	Protection Relay	1
X40-1260-22	Volume Control Assembly	1
X40-1270-18	Front Panel Board	1
X40-1280-09	Main Power Supply Board	1
X40-1290-14	Tuner Module Assembly	1

Note: Order parts through authorized Kenwood service centers only.

Troubleshooting Guide

Common symptoms, probable causes, and corrective actions.

Symptom	Probable Cause	Corrective Action
No power	Blown fuse, power switch	Check F901, F902; verify power switch operation
No audio output	Protection circuit, amplifier IC	Check protection relay; measure amplifier IC voltages
Distorted audio	Bias current, DC offset	Adjust bias current; null DC offset at outputs
Intermittent operation	Cold solder joints, connectors	Inspect solder joints; clean and reseat connectors
Hum or noise	Grounding, capacitors	Check ground connections; test filter capacitors
Tuner not working	Tuner power, alignment	Verify tuner module power supply; check alignment

Service Contact: Authorized Kenwood Service Center 1-800-536-9663