• Code: C7810
• Description: Outer thermistor short-circuited
• Causes: The input sampling value of the temperature/humidity sensor (outer thermistor) is at the reference value or less
• Remedy: 1 Checking the wire The wire is not properly connected or is faulty. Reinsert the following wire connectors, and replace the wire when it has no continuity.• Temperature/humidity sensor - Engine PWB Electrical Diagram of PWBs 2 Replacing the temperature/ humidity sensor The temperature/humidity sensor is faulty. Replace the temperature/ humidity sensor. 3 Firmware upgrade The firmware is not the latest version. Upgrade the engine firmware to the latest version Firmware Upgrade 4 Replacing the engine PWB The engine PWB is faulty. Replace the engine PWB. Engine PWB Replacement

• Code: C7901
• Description: Drum unit BK EEPROM error
• Causes: 1. No response from the device is detected for 5s or more 5 times continuously when reading / writing the data.2. The reading data of 2 points mismatches 8 times continuously.3. The reading data and the writing data mismatch 8 times continuously.
• Remedy: 1 Resetting the main power The data stored in the EEPROM in the drum unit is faulty. Turn the power switch and the main power switch off . After 5s passes, turn the main power switch and the power switch on. 2 Reinstalling the drum unit The drum unit is not properly installed. Reinstall drum unit BK so that the connector firmly connects. Drum Unit Replacement 3 Checking the wire The wire is not properly connected or is faulty. Reinsert the following wire connectors, and replace the wires when they have no continuity.• Drum/developer relay PWB - Feed image PWB• Feed image PWB - Engine PWB Electrical Diagram of PWBs 4 Drum unit replacement The EEPROM in the drum unit is faulty. Replace drum unit BK. Drum Unit Replacement 5 Replacing the drum/developer relay PWB The drum/developer relay PWB is faulty. Replace the drum/developer relay PWB. Drum/ Developer Relay PWB Replacement 6 Firmware upgrade The firmware is not the latest version. Upgrade the engine firmware to the latest version Firmware Upgrade 7 Replacing the feed image PWB The feed image PWB is faulty. Replace the feed image PWB.

• Code: C7902
• Description: Drum unit C EEPROM error Object: Color models
• Causes: 1. No response from the device is detected for 5s or more 5 times continuously when reading / writing the data.2. The reading data of 2 points mismatches 8 times continuously.3. The reading data and the writing data mismatch 8 times continuously.
• Remedy: 1 Resetting the main power The data stored in the EEPROM in the drum unit is faulty. Turn the power switch and the main power switch off . After 5s passes, turn the main power switch and the power switch on. 2 Reinstalling the drum unit The drum unit is not properly installed. Reinstall drum unit C so that the connector firmly connects. Drum Unit Replacement 3 Checking the wire The wire is not properly connected or is faulty. Reinsert the following wire connectors, and replace the wires when they have no continuity.• Drum/developer relay PWB - Feed image PWB• Feed image PWB - Engine PWB Electrical Diagram of PWBs 4 Drum unit replacement The EEPROM in the drum unit is faulty. Replace drum unit C. Drum Unit Replacement 5 Replacing the drum/developer relay PWB The drum/developer relay PWB is faulty. Replace the drum/developer relay PWB. Drum/ Developer Relay PWB Replacement 6 Firmware upgrade The firmware is not the latest version. Upgrade the engine firmware to the latest version Firmware Upgrade 7 Replacing the feed image PWB The feed image PWB is faulty. Replace the feed image PWB.

• Code: C7903
• Description: Drum unit M EEPROM error Object: Color models
• Causes: 1. No response from the device is detected for 5s or more 5 times continuously when reading / writing the data.2. The reading data of 2 points mismatches 8 times continuously.3. The reading data and the writing data mismatch 8 times continuously.
• Remedy: 1 Resetting the main power The data stored in the EEPROM in the drum unit is faulty. Turn the power switch and the main power switch off . After 5s passes, turn the main power switch and the power switch on. 2 Reinstalling the drum unit The drum unit is not properly installed. Reinstall drum unit M so that the connector firmly connects. Drum Unit Replacement 3 Checking the wire The wire is not properly connected or is faulty. Reinsert the following wire connectors, and replace the wires when they have no continuity.• Drum/developer relay PWB - Feed image PWB• Feed image PWB - Engine PWB Electrical Diagram of PWBs 4 Drum unit replacement The EEPROM in the drum unit is faulty. Replace drum unit M. Drum Unit Replacement 5 Replacing the drum/developer relay PWB The drum/developer relay PWB is faulty. Replace the drum/developer relay PWB. Drum/ Developer Relay PWB Replacement 6 Firmware upgrade The firmware is not the latest version. Upgrade the engine firmware to the latest version Firmware Upgrade 7 Replacing the feed image PWB The feed image PWB is faulty. Replace the feed image PWB.

• Code: C7904
• Description: Drum unit Y EEPROM error Object: Color models
• Causes: 1. No response from the device is detected for 5s or more 5 times continuously when reading / writing the data.2. The reading data of 2 points mismatches 8 times continuously.3. The reading data and the writing data mismatch 8 times continuously.
• Remedy: 1 Resetting the main power The data stored in the EEPROM in the drum unit is faulty. Turn the power switch and the main power switch off . After 5s passes, turn the main power switch and the power switch on. 2 Reinstalling the drum unit The drum unit is not properly installed. Reinstall drum unit Y so that the connector firmly connects. Drum Unit Replacement 3 Checking the wire The wire is not properly connected or is faulty. Reinsert the following wire connectors, and replace the wires when they have no continuity.• Drum/developer relay PWB - Feed image PWB• Feed image PWB - Engine PWB Electrical Diagram of PWBs 4 Drum unit replacement The EEPROM in the drum unit is faulty. Replace drum unit Y. Drum Unit Replacement 5 Replacing the drum/developer relay PWB The drum/developer relay PWB is faulty. Replace the drum/developer relay PWB. Drum/ Developer Relay PWB Replacement 6 Firmware upgrade The firmware is not the latest version. Upgrade the engine firmware to the latest version Firmware Upgrade 7 Replacing the feed image PWB The feed image PWB is faulty. Replace the feed image PWB.

• Code: C7911
• Description: Developer unit BK EEPROM error
• Causes: 1. No response from the device is detected for 5s or more 5 times continuously when reading / writing the data.2. The reading data of 2 points mismatches 8 times continuously.3. The reading data and the writing data mismatch 8 times continuously.
• Remedy: 1 Resetting the main power The data stored in the EEPROM in the developer unit is faulty. Turn the power switch and the main power switch off . After 5s passes, turn the main power switch and the power switch on. 2 Reinstalling the developer unit The developer unit is not properly installed. Reinstall developer unit BK so that the connector firmly connects. Drum Unit Replacement 3 Checking the wire The wire is not properly connected or is faulty. Reinsert the following wire connectors, and replace the wires when they have no continuity.• Drum/developer relay PWB - Feed image PWB• Feed image PWB - Engine PWB Electrical Diagram of PWBs 4 Developer unit replacement The EEPROM in the developer unit is faulty. Replace the developer unit BK. Developer Unit Replacement 5 Firmware upgrade The firmware is not the latest version. Upgrade the engine firmware to the latest version Firmware Upgrade 6 Replacing the drum/developer relay PWB The drum/developer relay PWB is faulty. Replace the drum/developer relay PWB. Drum/ Developer Relay PWB Replacement 7 Checking the feed image PWB The feed image PWB is faulty. Replace the feed image PWB.

• Code: C7912
• Description: Developer unit C EEPROM error Object: Color models
• Causes: 1. No response from the device is detected for 5s or more 5 times continuously when reading / writing the data.2. The reading data of 2 points mismatches 8 times continuously.3. The reading data and the writing data mismatch 8 times continuously
• Remedy: 1 Resetting the main power The data stored in the EEPROM in the developer unit is faulty. Turn the power switch and the main power switch off . After 5s passes, turn the main power switch and the power switch on. 2 Reinstalling the developer unit The developer unit is not properly installed. Reinstall developer unit C so that the connector firmly connects. Developer Unit Replacement 3 Checking the wire The wire is not properly connected or is faulty. Reinsert the following wire connectors, and replace the wires when they have no continuity.• Drum/developer relay PWB - Feed image PWB• Feed image PWB - Engine PWB Electrical Diagram of PWBs 4 Developer unit replacement The EEPROM in the developer unit is faulty. Replace the developer unit C. Developer Unit Replacement 5 Firmware upgrade The firmware is not the latest version. Upgrade the engine firmware to the latest version Firmware Upgrade 6 Replacing the drum/developer relay PWB The drum/developer relay PWB is faulty. Replace the drum/developer relay PWB. Drum/ Developer Relay PWB Replacement 7 Checking the feed image PWB The feed image PWB is faulty. Replace the feed image PWB.

• Code: C7913
• Description: Developer unit M EEPROM error Object: Color models
• Causes: 1. No response from the device is detected for 5s or more 5 times continuously when reading / writing the data.2. The reading data of 2 points mismatches 8 times continuously.3. The reading data and the writing data mismatch 8 times continuously.
• Remedy: 1 Resetting the main power The data stored in the EEPROM in the developer unit is faulty. Turn the power switch and the main power switch off . After 5s passes, turn the main power switch and the power switch on. 2 Reinstalling the developer unit The developer unit is not properly installed. Reinstall developer unit M so that the connector firmly connects. Developer Unit Replacement 3 Checking the wire The wire is not properly connected or is faulty. Reinsert the following wire connectors, and replace the wires when they have no continuity.• Drum/developer relay PWB - Feed image PWB• Feed image PWB - Engine PWB Electrical Diagram of PWBs 4 Developer unit replacement The EEPROM in the developer unit is faulty. Replace the developer unit M. Developer Unit Replacement 5 Firmware upgrade The firmware is not the latest version. Upgrade the engine firmware to the latest version Firmware Upgrade 6 Replacing the drum/developer relay PWB The drum/developer relay PWB is faulty. Replace the drum/developer relay PWB. Drum/ Developer Relay PWB Replacement 7 Checking the feed image PWB The feed image PWB is faulty. Replace the feed image PWB.