Marantz SR 18 Service Manual

The Marantz SR 18 is a high-performance AV receiver featuring Dolby Digital and DTS decoding, 100W per channel (8 ohms), 6-channel discrete amplifier, digital optical/coaxial inputs, component video switching, multi-room capability, RS-232 control interface, and advanced audio processing. This service manual provides technical information for qualified service personnel including schematics, alignment procedures, troubleshooting, and parts lists.

1. Technical Specifications 2. Block Diagrams 3. Circuit Descriptions 4. Disassembly Procedures 5. Test Points & Measurements 6. Alignment Procedures 7. Troubleshooting Flowcharts 8. Parts List 9. PCB Layouts 10. Schematics 11. Service Notes

Technical Specifications

Detailed technical specifications for the Marantz SR 18 AV receiver.

ParameterSpecification
Power Output100W x 6 (8 ohms, 20Hz-20kHz, 0.08% THD)
Frequency Response10Hz-100kHz (+1/-3dB)
Signal-to-Noise Ratio100dB (line input)
Total Harmonic Distortion0.08% (rated power)
Input Sensitivity200mV (line), 800mV (digital)
Digital Inputs3 optical, 2 coaxial
Video Inputs3 composite, 2 S-video, 2 component
Audio Inputs6 line level, phono, 6-channel direct
Dimensions440 x 161 x 464mm (W x H x D)
Weight14.5 kg

Block Diagrams

System block diagrams showing signal flow and major components.

  1. Main System Block Diagram: Shows overall signal path from inputs to outputs.
  2. Power Supply Block Diagram: Illustrates AC input, transformers, and DC regulation.
  3. Audio Processing Block Diagram: Details DSP, DAC, and analog stages.
  4. Video Processing Block Diagram: Shows video switching and enhancement circuits.
  5. Control System Block Diagram: Microprocessor and interface circuits.

WARNING! High voltages present in power supply section. Exercise extreme caution when servicing.

Circuit Descriptions

Detailed descriptions of major circuit sections.

  1. Power Supply Circuit: Switching power supply with multiple regulated outputs.
  2. Amplifier Section: Discrete 6-channel power amplifier with protection circuits.
  3. Digital Audio Board: DSP processor, DAC circuits, and digital interfaces.
  4. Analog Audio Board: Phono stage, line level inputs, and tone control circuits.
  5. Video Board: Component video switching and processing circuits.
  6. Control Board: Microprocessor, display driver, and front panel controls.

CAUTION! Static-sensitive components present. Use proper ESD precautions.

Disassembly Procedures

Test Points & Measurements

Critical test points and measurement procedures for service diagnostics.

Power Supply Test Points: TP1: +12V, TP2: -12V, TP3: +5V, TP4: +3.3V, TP5: +48V (amp supply)

Audio Section Tests: Oscillator input 1kHz, measure output at speaker terminals. Verify distortion <0.1% at 50W.

Digital Section: Check clock signals at X1 (16.9344MHz) and X2 (11.2896MHz).

Protection Circuits: Test DC detection, over-current, and thermal protection functions.

Alignment Procedures

Factory alignment procedures for critical circuits.

  1. Power Supply Adjustment: VR1 for +12V, VR2 for +5V using digital voltmeter.
  2. Bias Current Adjustment: VR101-VR106 for 20mA quiescent current per channel.
  3. DC Offset Adjustment: VR201-VR206 for 0V ±5mV at speaker outputs.
  4. DSP Processor: Software calibration via service mode (enter with front panel combination).
  5. Display Brightness: VR301 for LED intensity adjustment.

Tip: Use calibrated test equipment and allow 30 minutes warm-up before adjustments.

Troubleshooting Flowcharts

No power, no sound, protection mode, no display, digital input issues.

SymptomPossible CauseCorrective Action
No PowerFuse, power supplyCheck F101 (5A), test power supply outputs, check Q101-Q104.
Protection ModeDC offset, short circuitMeasure DC at outputs, check output transistors, test protection IC IC501.
No SoundMute circuit, DSPCheck mute transistors Q201-Q206, test DSP clock, reset signals.
No DisplayDisplay driver, powerTest +5V to display, check data lines, replace display driver IC301.
Digital Input FailOptical receiver, S/PDIFTest optical receivers IC601-IC603, check S/PDIF input circuits.

Parts List

Complete parts list with manufacturer part numbers.

Part NumberDescriptionQty
2SC5200Power Transistor NPN12
2SA1943Power Transistor PNP12
IC STA505DSP Processor1
IC NJM4580Dual Op-Amp8
F101Fuse 5A 250V1
C101Capacitor 10000uF 63V2
TR101Power Transformer1
X1Crystal 16.9344MHz1

PCB Layouts

Printed circuit board layouts for all major assemblies.

  1. Main Board: Top and bottom layer views with component locations.
  2. Power Supply Board: Component side and solder side layouts.
  3. Front Panel Board: Control and display circuit layout.
  4. Audio Input Board: Analog input circuitry layout.
  5. Heat Sink Assembly: Mechanical drawing with mounting details.

WARNING! Observe polarity markings on electrolytic capacitors.

Schematics

Complete schematic diagrams for all circuit sections.

Service Notes

Important service bulletins and technical updates.

Service BulletinIssueSolution
SN001Overheating in multi-channel modeAdd thermal compound, ensure heat sink contact
SN002Digital dropout with certain sourcesReplace IC601 with revised version
SN003Display flicker in bright environmentsAdjust VR301, add light shield if needed
SN004Hum in phono inputCheck grounding, add shield to phono cables
SN005Remote control intermittentClean IR window, check C301 value

Reset Procedures: Service mode access: Hold TONE + SURROUND while powering on.

Service Support: Marantz Technical Support: 1-800-288-2284

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