Marantz 2238B Stereo Service Manual

The Marantz 2238B is a classic stereo receiver from the 1970s featuring 38 watts per channel RMS power, dual tuning meters, phono inputs for turntables, tape monitor circuits, loudness compensation, and Marantz's signature warm sound quality. This service manual covers technical specifications, circuit diagrams, alignment procedures, troubleshooting, and maintenance guidelines for qualified service technicians.

1. Technical Specifications 2. Block Diagram Overview 3. Circuit Descriptions 4. Alignment Procedures 5. Parts List 6. Schematic Diagrams 7. PCB Layouts 8. Test Points & Voltages 9. Troubleshooting Guide 10. Service Adjustments 11. Safety Precautions

Technical Specifications

Complete electrical and performance specifications for the Marantz 2238B stereo receiver.

Parameter	Specification
Power Output	38 watts per channel RMS (8 ohms, 20Hz-20kHz)
Total Harmonic Distortion	0.1% at rated output
Frequency Response	10Hz - 50kHz (+0, -1dB)
Input Sensitivity	Phono: 2.0mV; Aux: 150mV
Signal-to-Noise Ratio	Phono: 75dB; Aux: 90dB
Tuning Range	FM: 88-108MHz; AM: 530-1620kHz
Dimensions	17-3/8" W × 5-1/4" H × 14-1/4" D
Weight	22.5 lbs (10.2 kg)
Power Requirements	120V AC, 60Hz, 180W
Speaker Impedance	4-16 ohms

Block Diagram Overview

System block diagram showing signal flow and major circuit sections.

Input Selector: Phono, Aux, Tape 1, Tape 2
Phono Preamp: RIAA equalization
Tone Control: Bass, Treble, Loudness
Power Amplifier: Complementary symmetry output
FM Tuner: Front end, IF, MPX
Power Supply: Transformer, rectifiers, regulators
Protection Circuit: Speaker relay, overload

WARNING! High voltages present - discharge capacitors before servicing.

Circuit Descriptions

Detailed description of each major circuit section.

Power Supply: Dual secondary transformer with bridge rectification
Amplifier Section: Direct coupling, complementary output transistors
Phono Stage: Low-noise transistors with RIAA equalization
FM Tuner: 4-gang variable capacitor, ceramic filters
Protection Circuit: DC detection, thermal protection
Control Section: Potentiometers, switches, tone controls

CAUTION! Use isolation transformer when testing live circuits.

Alignment Procedures

FM Front End: Adjust oscillator and RF coils for proper tracking
IF Alignment: 10.7MHz ceramic filter alignment
MPX Decoder: 19kHz pilot carrier and 38kHz subcarrier adjustment
AM Tuner: Oscillator and antenna coil alignment
DC Offset: Adjust for 0mV at speaker terminals
Bias Current: Set idle current per specification

Parts List

Complete component listing with manufacturer part numbers.

Reference	Description	Part Number
Q701-Q704	Output Transistor 2SC1116	112-0126
D701-D704	Rectifier Diode 1S1886	112-0089
C701,C702	Main Filter 4700µF/50V	112-0155
R701,R702	Emitter Resistor 0.47Ω/5W	112-0033
IC701	Power Regulator HA1301	112-0201

Schematic Diagrams

Complete schematic diagrams for all circuit boards.

Main Amplifier Board P700
Power Supply Board P800
Tuner Assembly P300
Control Board P400
Protection Circuit Board P900
Front Panel Assembly

Tip: Refer to voltage charts when troubleshooting.

PCB Layouts

Printed circuit board layouts with component placement.

Component side and solder side views
Trace routing and via locations
Test point designations
Ground plane areas
Heatsink mounting points
Connector pin assignments

WARNING! Observe polarity when replacing capacitors.

Test Points & Voltages

Critical test points and expected voltage readings.

Test Point	Voltage (DC)	Description
TP701	+42V	Positive rail
TP702	-42V	Negative rail
TP703	0V	Speaker output (idle)
TP801	+28V	Regulated supply
TP802	+15V	Preamp supply

Troubleshooting Guide

Common problems and solutions for the 2238B receiver.

Symptom	Possible Cause	Corrective Action
No power	Fuse, power switch	Check F701 (4A), power switch contacts
Distorted audio	Output transistors	Test Q701-Q704, check bias current
No FM reception	Tuner section	Check voltages on tuner board, alignment
Hum in output	Filter capacitors	Replace C701, C702, check grounds
Protection trips	DC offset, short	Measure DC at outputs, check speakers

Service Adjustments

Procedures for routine maintenance and calibration.

Bias Adjustment: VR701 for 20mA idle current
DC Offset: VR702 for 0mV output
Meter Calibration: VR301 for signal strength
Dolby Level: VR401 for tape playback
Output Balance: VR703 for channel balance

CAUTION! Use plastic tools when adjusting trimmers.

Safety Precautions

Important safety information for service personnel.

This equipment contains hazardous voltages. Always disconnect power before servicing. Use isolation transformer for live measurements. Discharge large capacitors before handling. Observe component ratings and replacements. Use proper grounding techniques. Follow ESD precautions for semiconductors.