Marantz 4220 Service Manual

The Marantz 4220 is a classic quadraphonic receiver from the 1970s featuring 4-channel stereo, discrete 4-channel, and synthesized 4-channel modes. This service manual covers technical specifications, circuit diagrams, alignment procedures, troubleshooting, and maintenance for qualified service technicians. The unit includes front/rear amplifier channels, Dolby noise reduction, and comprehensive input/output connectivity.

1. Technical Specifications 2. Block Diagrams 3. Circuit Descriptions 4. Alignment Procedures 5. Parts List 6. PCB Layouts 7. Voltage Measurements 8. Troubleshooting Guide 9. Service Adjustments 10. Safety Precautions 11. Schematics

Technical Specifications

Complete electrical and performance specifications for the Marantz 4220 quadraphonic receiver.

Parameter	Specification
Power Output	20W per channel (4 channels)
Total Harmonic Distortion	<0.5% at rated power
Frequency Response	20Hz - 20kHz ±1dB
Input Sensitivity	Phono: 2.5mV; Aux: 150mV
Signal-to-Noise Ratio	Phono: 65dB; Aux: 75dB
Damping Factor	>30 at 8 ohms
Speaker Impedance	4-16 ohms
Power Requirements	120V AC, 60Hz, 180W
Dimensions	17.5" W × 5.25" H × 14.5" D
Weight	22 lbs

Block Diagrams

System block diagrams showing signal flow and functional relationships between circuits.

Main System Block Diagram: Overall signal path from inputs to outputs
Preamplifier Section: Phono, aux, and tape input stages
Power Amplifier Section: Four-channel output stages
Power Supply Section: Voltage regulation and distribution
Control Logic: Mode switching and function selection

NOTE: Refer to schematics for detailed component-level information.

Circuit Descriptions

Detailed descriptions of major circuit sections and their operation.

Preamplifier Stage: Dual-stage phono equalization with low-noise transistors
Tone Control: Bass and treble controls with center detents
Volume/Balance: Ganged potentiometers for four-channel control
Power Amplifier: Complementary symmetry output with thermal protection
Power Supply: Dual-voltage supply with bridge rectification
Mode Switching: Logic circuits for stereo/quad mode selection

Alignment Procedures

Step-by-step alignment and calibration procedures for optimal performance.

DC Offset Adjustment: Set output transistor bias currents
Idling Current: Adjust for minimum crossover distortion
Phono Equalization: Align RIAA response curve
Dolby Alignment: Set Dolby B noise reduction levels
Mode Switching: Verify proper quadraphonic mode operation
Meter Calibration: Adjust VU meters for accurate reading

WARNING! Use calibrated test equipment and follow procedures exactly.

Parts List

Complete listing of components with manufacturer part numbers and values.

Reference Designator	Description	Value/Part Number
Q101-Q104	Input Transistor	2SC458
Q201-Q208	Driver Transistor	2SC945
Q301-Q304	Output Transistor	2SC1061
D101-D108	Rectifier Diode	1S1886
C201-C204	Filter Capacitor	2200μF/35V
R101-R124	Carbon Film Resistor	Various values
VR101-VR104	Trimmer Potentiometer	500Ω

PCB Layouts

Printed circuit board layouts showing component placement and trace routing.

Main Amplifier Board: Power output and driver stages
Preamplifier Board: Input switching and tone controls
Power Supply Board: Transformer, rectifiers, and filters
Control Board: Mode switching and indicator circuits
Front Panel Board: Switches, potentiometers, and meters

Tip: Use these layouts for component location and troubleshooting.

Voltage Measurements

Reference voltage measurements at key test points throughout the circuit.

Test Point	Normal Voltage	Tolerance
TP1 (+B)	+28V DC	±2V
TP2 (-B)	-28V DC	±2V
TP3 (Vcc)	+15V DC	±1V
TP4 (GND)	0V	Reference
TP5 (Bias)	+0.65V DC	±0.1V
TP6 (Offset)	0V DC	±50mV

CAUTION! Measure with high-impedance digital multimeter.

Troubleshooting Guide

Systematic approach to diagnosing and repairing common problems.

Symptom	Possible Cause	Corrective Action
No sound all channels	Power supply failure	Check fuses, transformer, rectifiers
Distortion in one channel	Output transistor failure	Replace matched output pair
Intermittent operation	Cold solder joints	Resolder all connections on main board
Hum in audio	Filter capacitor failure	Replace main filter capacitors
Mode switching erratic	Switch contacts dirty	Clean with contact cleaner
Meters not working	Meter movement damaged	Replace meter assembly

Service Adjustments

Routine maintenance and performance optimization procedures.

Bias Current Adjustment: Set for 20mA per output pair
DC Offset Nulling: Adjust for 0V DC at speaker outputs
Phono Sensitivity: Calibrate for standard 2.5mV input
Dolby Level: Set for proper Dolby B tracking
Meter Zero: Adjust mechanical zero of VU meters
Mode Indicator: Verify proper LED operation

WARNING! Disconnect from AC power before making internal adjustments.

Safety Precautions

Essential safety information for service technicians.

Always disconnect AC power before servicing
Use isolation transformer when testing live circuits
Discharge large capacitors before handling
Replace fuses with same type and rating
Ensure proper grounding of test equipment
Work in well-ventilated area

DANGER! Lethal voltages present - exercise extreme caution.

Schematics

Complete circuit diagrams for all sections of the Marantz 4220.

Main Schematic: Overall system circuit diagram
Power Supply: Transformer, rectification, and regulation
Preamplifier: Phono, aux, and tape input circuits
Power Amplifier: Four-channel output stages
Control Circuits: Mode switching and logic
Front Panel: Switches, indicators, and controls

Note: These schematics are for qualified service personnel only.