Marantz PM8004 Service Manual

The Marantz PM8004 is a high-performance integrated stereo amplifier featuring 70W per channel (8Ω), high-current power supply, discrete power amplifier configuration, Marantz HDAM (Hyper Dynamic Amplifier Module) circuits, toroidal transformer, gold-plated terminals, and comprehensive input/output options including phono MM, CD, and line inputs. Below are key sections for technical specifications, circuit diagrams, adjustment procedures, troubleshooting, and service information.

1. Technical Specifications 2. Block Diagram 3. Circuit Description 4. Adjustment Procedures 5. Parts List 6. PCB Layouts 7. Wiring Diagrams 8. Troubleshooting Guide 9. Service Notes 10. Safety Precautions 11. Test Points & Measurements

Technical Specifications

Key performance parameters and electrical characteristics of the Marantz PM8004 amplifier.

Parameter	Specification
Rated Output Power	70W + 70W (8Ω, 20Hz-20kHz, 0.08% THD)
Dynamic Power	100W + 100W (8Ω), 150W + 150W (4Ω)
Total Harmonic Distortion	0.08% (20Hz-20kHz, 8Ω)
Frequency Response	5Hz-100kHz (+1/-3dB)
Input Sensitivity	200mV (CD), 2.5mV (Phono MM)
Signal-to-Noise Ratio	100dB (CD), 87dB (Phono MM)
Damping Factor	100 (8Ω, 1kHz)
Power Consumption	280W (max), 0.3W (standby)
Dimensions	440 × 128 × 397mm (W×H×D)
Weight	11.8kg

Block Diagram

System architecture showing signal flow and major functional blocks.

Input Selector: CD, TUNER, AUX, PHONO, TAPE
Phono Equalizer: RIAA equalization for MM cartridges
Tone Control: Bass/Treble adjustment circuits
Volume Control: ALPS motorized potentiometer
HDAM Circuits: Current feedback amplification stages
Power Amplifier: Discrete output stage with complementary transistors
Power Supply: Toroidal transformer with dual rectifiers
Protection Circuit: DC detection, thermal protection

WARNING! High voltage present in power supply section. Disconnect power before servicing.

Circuit Description

Detailed explanation of major circuit sections and their operation.

Input Stage: JFET input buffers for high impedance
HDAM Modules: Discrete op-amp circuits for superior transient response
Phono Stage: Low-noise transistor array with RIAA precision
Power Amplifier: Triple Darlington configuration with thermal tracking
Power Supply: Dual mono design with separate windings
Protection: Microprocessor-controlled relay protection

CAUTION! Static-sensitive components. Use grounded wrist strap when handling PCBs.

Adjustment Procedures

DC Offset: Adjust VR801/VR802 for 0mV ±5mV at speaker terminals
Bias Current: Set VR803/VR804 for 10mV across emitter resistors
Phono Balance: Adjust VR101 for equal channel output
Protection Delay: Verify 3-5 second delay on power-on
Test Equipment: Oscilloscope, DMM, audio generator, dummy loads
Test Conditions: 1kHz sine wave, 8Ω load, 1W output unless specified

Parts List

Complete component listing with manufacturer part numbers and specifications.

Semiconductors: 2SC2240/2SA970 (small signal), 2SC2705/2SA1145 (driver), 2SC5200/2SA1943 (output). ICs: NJM2068 (phono), NJM4558 (tone control). Transformers: Toroidal 300VA. Capacitors: ELNA for audio, Nichicon for power supply.

PCB Layouts

Main board, power supply board, and front panel board layouts with component locations.

Main Amplifier Board: P8001 - Power transistors, driver circuits
Power Supply Board: P8002 - Rectifiers, filter capacitors
Input/Control Board: P8003 - Selector switches, volume control
Phono Board: P8004 - MM equalizer circuit

Tip: Refer to silk screen markings for component orientation.

Wiring Diagrams

Internal wiring connections between boards, connectors, and front panel controls.

Disconnect AC power before examining wiring
Check connector CN8001 for main power supply connections
Verify CN8002 for speaker relay connections
Inspect CN8003 for front panel control wiring
Confirm CN8004 for input selector connections

WARNING! Mains voltage present even when switched off. Disconnect from AC outlet.

Troubleshooting Guide

Systematic approach to diagnosing common amplifier faults.

Symptom	Possible Cause	Corrective Action
No power	Fuse, power switch, transformer	Check F801/F802; verify AC input; test transformer primary
No sound	Protection circuit, muting relay	Check DC offset; test relay K801; verify protection IC
Distortion	Bias current, output transistors	Adjust bias; test output devices; check driver transistors
Hum/buzz	Grounding, filter capacitors	Verify ground connections; test C801-C804; check input shielding
Channel imbalance	Volume control, input selector	Clean potentiometer; test input switching; verify preamp stage

Service Notes

Important service information and common repair procedures.

Replacement transistors must be matched pairs. Thermal compound required for output devices. Allow 30 minutes warm-up for accurate bias adjustment. Use original Marantz parts for critical audio path components.

Safety Precautions

Essential safety procedures for service technicians.

Always use isolation transformer when testing live circuits. Discharge large capacitors before handling. Use appropriate PPE when working with high temperatures. Follow ESD precautions with sensitive components.

CAUTION! Lethal voltages present. Qualified technicians only.

Test Points & Measurements

Key test points for performance verification and alignment.

Test Point	Normal Value	Measurement
TP801/TP802	0mV ±5mV	DC Offset (no signal)
TP803/TP804	10mV ±2mV	Bias Current (idle)
TP805	±55V DC	Main Rail Voltage
TP806	±15V DC	Preamp Supply
TP807	+5V DC	Control Circuit

Service Contact: Authorized Marantz service centers only

Technical Support: Refer to Marantz service portal for latest updates