Marantz Model 22 Service Manual

The Marantz Model 22 is a classic stereo receiver featuring 22 watts per channel RMS power output, high-quality audio amplification, FM/AM tuner sections, and the renowned Marantz build quality. This service manual provides comprehensive technical information for servicing, troubleshooting, and maintaining this iconic audio component. Below are key sections covering specifications, circuit descriptions, alignment procedures, parts lists, and troubleshooting guides.

1. Technical Specifications 2. Circuit Description 3. Block Diagrams 4. Alignment Procedures 5. Schematic Diagrams 6. Parts List 7. PCB Layouts 8. Voltage Charts 9. Troubleshooting Guide 10. Service Notes 11. Safety Precautions

Technical Specifications

Complete electrical and mechanical specifications for the Marantz Model 22 stereo receiver.

ParameterSpecification
Power Output22 watts per channel RMS (8 ohms, 20Hz-20kHz)
Total Harmonic DistortionLess than 0.3% at rated output
Frequency Response20Hz - 20kHz ±1dB
Input SensitivityPhono: 2.5mV; Aux: 250mV
Signal-to-Noise RatioPhono: 70dB; Aux: 85dB
FM Tuner Section87.5-108 MHz, 1.8μV sensitivity
AM Tuner Section530-1620 kHz
Dimensions16.5" W × 5.25" H × 14.5" D
Weight22 lbs (10 kg)
Power Requirements120V AC, 60Hz, 150W

Circuit Description

Detailed explanation of the Model 22's circuit topology and design philosophy.

  1. Power Supply: Dual secondary transformer with full-wave rectification and capacitor filtering
  2. Preamplifier Stage: Discrete transistor phono equalization and line amplification
  3. Power Amplifier: Complementary symmetry output stage with driver transistors
  4. FM Tuner: FET front end with 4-gang variable capacitor, IC IF section
  5. AM Tuner: Standard superheterodyne design with ferrite rod antenna
  6. Tone Controls: Bass and treble controls with center detents
  7. Protection Circuitry: Fuse protection and thermal considerations

NOTE: All circuits use high-quality components selected for audio performance and reliability.

Block Diagrams

System-level block diagrams showing signal flow and interconnections.

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

Alignment Procedures

Step-by-step alignment instructions for FM and AM tuner sections.

  1. FM IF Alignment: Adjust IF transformers for maximum output and proper bandwidth
  2. FM Front End: Align RF and oscillator circuits for proper tracking
  3. FM Detector: Adjust quadrature detector for minimum distortion
  4. AM Alignment: Adjust IF and oscillator circuits for proper reception
  5. Stereo Decoder: Adjust 19kHz and 38kHz circuits for proper stereo separation

REQUIRED EQUIPMENT: RF signal generator, oscilloscope, digital voltmeter, and alignment tools.

Schematic Diagrams

Complete schematic diagrams for all circuit sections.

NOTE: All component values and designations clearly marked.

Parts List

Complete listing of all components with manufacturer part numbers.

ComponentDescriptionPart Number
Output Transistors2N3055/MJ2955 complementary pairM22-101
Power TransformerDual secondary 35V-0-35VM22-201
Main Filter Capacitors4700μF 50V electrolyticM22-301
FM Tuner ICTA7303P FM IF amplifier/detectorM22-401
Volume ControlDual 100kΩ audio taper potentiometerM22-501
Selector Switch6-position rotary switchM22-601
Power Cord3-conductor AC power cordM22-701
Fuse2A 250V slow-blowM22-801

PCB Layouts

Printed circuit board layouts for all major assemblies.

  1. Main Amplifier Board: Component placement and trace routing
  2. Preamplifier Board: Low-level audio circuit layout
  3. Power Supply Board: Rectification and filtering components
  4. FM Tuner Board: RF and IF section layout
  5. Control Board: Switches and potentiometers

NOTE: All boards use fiberglass substrate with solder mask and silkscreen.

Voltage Charts

DC voltage measurements at key test points under normal operating conditions.

Test PointVoltage (DC)Notes
Main B++42VMeasured at filter capacitor
Output Stage+21VCenter point of output stage
Driver Stage+35VDriver transistor collectors
Preamplifier+24VRegulated supply for preamp
Tuner Section+12VRegulated supply for tuner
Phono Stage+18VPhono equalization supply

CAUTION: Voltages measured with no signal input and volume at minimum.

Troubleshooting Guide

Systematic approach to diagnosing and repairing common issues.

SymptomPossible CauseCorrective Action
No powerBlown fuse, power switch, transformerCheck fuse; test power switch; measure transformer primary
No audio outputOutput transistors, driver stage, protection circuitCheck output transistors; test driver stage voltages
Distorted audioBias adjustment, leaky capacitors, failing transistorsAdjust bias current; test coupling capacitors; check transistors
No FM receptionRF stage, local oscillator, IF alignmentCheck FET front end; verify oscillator operation; realign IF
Hum in audioGround loops, filter capacitors, poor connectionsCheck ground connections; test filter capacitors; inspect wiring
Intermittent operationCold solder joints, failing components, thermal issuesInspect solder joints; test components under heat; check for overheating

Service Notes

Important technical notes and modifications for service technicians.

WARNING: Only qualified technicians should perform service procedures.

Safety Precautions

Critical safety information for servicing high-voltage equipment.

  1. Disconnect Power: Always unplug unit before servicing
  2. Discharge Capacitors: Large filter capacitors can hold dangerous charge
  3. Use Isolation Transformer: Essential for live measurements
  4. Grounding: Ensure proper grounding of test equipment
  5. High Voltage: Power supply sections contain lethal voltages
  6. Heat Sinks: Output transistors and heat sinks can cause burns

DANGER: Lethal voltages present - exercise extreme caution.

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