Manual for A-U670/A-U671/NS-BP401/NS-BP301

To Service Personnel

• Critical Components: Components with special characteristics are marked with A and must be replaced with parts of equal specifications.
• Leakage Current Measurement (120V Models): After service, verify insulation of conductive surfaces. Meter impedance should be 1500 ohms shunted by 0.15 µF. Leakage current must not exceed 0.5mA. Test with AC plug in both polarities.
• Lead-Free Solder: Use Sn+Ag+Cu, Sn+Cu, or Sn+Zn+Bi. Note that lead-free solder has a higher melting point (30-40°C higher than lead solder), requiring a suitable soldering iron.
• Safety Measures: Internal parts may contain high voltages. Use insulating gloves. Capacitors retain dangerous charge even after power off; discharge with a 5 k-ohm/10 W resistor (approx. 30 seconds per capacitor).
• Measuring Instrument Handling: Due to BTL connected speaker output, the ground side of the measuring instrument must be floating.
• Disassembly: Follow numbered order. Disconnect power. Disassembly procedures for A-U670, A-670, and A-U671 are similar; A-U671 is shown as representative.
• Self-Diagnostic Function:
  • A-U670/A-670: Requires CD-NT670/CD-NT670D. Connect units with system cable. Display appears on CD unit.
  • A-U671: Uses unit's indicator for display. Functions include version checks, indicator checks, input checks, protection history, and factory reset.