The Marantz MA700 is a high-performance monaural power amplifier featuring advanced circuitry, robust power output, and professional-grade components. This service manual covers technical specifications, circuit diagrams, troubleshooting procedures, calibration instructions, and maintenance guidelines for qualified service technicians. Below are key sections for technical overview, specifications, block diagrams, adjustment procedures, and service information.
The MA700 monaural power amplifier utilizes high-current discrete output stages, toroidal power transformer, and advanced protection circuitry for reliable performance in professional and high-end audio applications.
| Component | Description |
|---|---|
| Power Transformer | Toroidal design for low magnetic leakage |
| Output Stage | Discrete transistors with high current capability |
| Protection Circuitry | DC offset, overcurrent, and thermal protection |
| Input Stage | Balanced and unbalanced inputs with selector |
| Power Supply | Dual rail supply with large filter capacitors |
| Heat Sink | Extruded aluminum with forced air capability |
| Binding Posts | Heavy-duty 5-way speaker terminals |
| RCA Inputs | Gold-plated unbalanced inputs |
| XLR Inputs | Professional balanced inputs |
| Power Switch | Main power with standby function |
System block diagram showing signal flow from input to output stages.
NOTE: Refer to schematic diagrams for detailed component values and connections.
Detailed explanation of major circuit sections and their operation.
Input Stage: JFET input differential pair with current source load provides high input impedance and low noise. Balanced inputs use instrumentation amplifier configuration.
Voltage Gain Stage: Cascode configuration with constant current source for high bandwidth and linearity. Local feedback networks determine gain characteristics.
Output Stage: Complementary symmetry with triple Darlington pairs for high current capability. Emitter resistors provide current sharing and thermal stability.
Protection Circuits: DC servo circuit maintains output offset below 10mV. VI limiter protects against short circuits. Thermal sensor shuts down amplifier at 85°C.
Factory calibration and adjustment procedures for service technicians.
WARNING! Use isolation transformer when servicing live circuits. Discharge power supply capacitors before working.
| Symptom | Possible Cause | Corrective Action |
|---|---|---|
| No output | Protection circuit active | Check for shorted outputs; measure DC offset; verify fuse integrity |
| Distorted sound | Bias current incorrect | Adjust bias current per procedure; check output transistors |
| Excessive hum | Ground loop/power supply | Verify grounding; check filter capacitors; inspect rectifier diodes |
| Intermittent operation | Thermal protection | Check fan operation; clean heatsink; verify thermal sensor |
| Channel imbalance | Gain mismatch | Measure and match gain between channels; check input selector |
| Protection LED lit | Fault condition | Reset amplifier; diagnose specific protection circuit |
Critical replacement parts with manufacturer part numbers.
| Part Number | Description | Qty |
|---|---|---|
| MA700-001 | Main PCB Assembly | 1 |
| MA700-002 | Power Supply PCB | 1 |
| MA700-003 | Toroidal Transformer | 1 |
| MA700-004 | Output Transistor Set | 2 |
| MA700-005 | Driver Transistor Set | 4 |
| MA700-006 | Main Filter Capacitors | 4 |
| MA700-007 | Thermal Sensor | 1 |
| MA700-008 | Front Panel Assembly | 1 |
| MA700-009 | Binding Post Set | 2 |
| MA700-010 | RCA/XLR Input Board | 1 |
Detailed printed circuit board layouts with component placement and trace routing.
NOTE: Use exact replacement parts to maintain performance and reliability.
Essential safety procedures for service personnel.
DANGER! Lethal voltages present in power supply section. Qualified personnel only.
Important service information and common repair procedures.
Warranty Service: Record serial number and date of service. Use only genuine Marantz parts.
Performance Verification: After repair, verify specifications meet original factory standards.
Documentation: Update service records with detailed repair information and test results.
Technical Support: Contact Marantz technical support for schematic updates and service bulletins.
Service Centers: Authorized service centers listed at www.marantz.com