• Code: C6400
• Description: Zero-cross signal error
  While fuser heater ON/OFF control is performed, the zero-cross signal is not input within 3 s.
• Causes: Defective PWB
• Remedy: Replace the power source PWB or engine PWB and check for correct operation.

• Code: C6410
• Description: Fuser unit connector insertion problem
  Absence of the fuser unit is detected.
• Causes: Fuser unit connector inserted incorrectly.
  Defective fuser unit connector.
• Remedy: Fuser unit connector inserted incorrectly. Reinsert the fuser unit connector if necessary.
  Defective fuser unit connector. Replace the fuser unit.

• Code: C7300
• Description: Toner container problem
  Toner level is not detected when toner empty is detected.
• Causes: Poor contact in the connector terminals.
  Defective toner container sensor.
• Remedy: Poor contact in the connector terminals. Check the connection of connector YC5 on the engine PWB and the continuity across the connector terminals. Repair or replace if necessary.
  Defective toner container sensor. Replace the toner container sensor.

• Code: C7400
• Description: Developing unit connector insertion problem Absence of the developing unit is detected.
• Causes: Developing unit connector inserted incorrectly.
  Defective developing unit connector.
• Remedy: Developing unit connector inserted incorrectly. Reinsert the developing unit connector if necessary.
  Defective developing unit connector. Replace the developing unit.

• Code: C7410
• Description: Drum unit connector insertion problem
  Absence of the drum unit is detected.
• Causes: Drum unit connector inserted incorrectly.
  Defective drum unit connector.
• Remedy: Drum unit connector inserted incorrectly. Reinsert the drum unit connector if necessary.
  Defective drum unit connector. Replace the drum unit.

• Code: C7800
• Description: Broken external thermistor wire
  The thermistor output value is 4.5 V or more.
• Causes: Poor contact in the connector terminals.
  Defective humidity sensor.
• Remedy: Poor contact in the connector terminals. Check the connection of connector YC10 on the engine PWB and the continuity across the connector terminals. Repair or replace if necessary.
  Defective humidity sensor. Replace the humidity sensor.

• Code: C7900
• Description: Drum EEPROM error
  Reading from or writing to EEPROM cannot be performed.
• Causes: Poor contact in the connector terminals.
  Defective drum unit.
• Remedy: Poor contact in the connector terminals. Check the connection of connector on the engine PWB and the continuity across the connector terminals. Repair or replace if necessary.
  Defective drum unit. Replace the drum unit.

• Code: C7910
• Description: Developing unit EEPROM error
  Reading from or writing to EEPROM cannot be performed.
• Causes: Poor contact in the connector terminals.
  Defective developing unit.
• Remedy: Poor contact in the connector terminals. Check the connection of connector on the engine PWB and the continuity across the connector terminals. Repair or replace if necessary.
  Defective developing unit. Replace the developing unit.