• Code: C610
• Description: Broken fixing unit thermistor wire • The fixing temperature does not increase for 40 s after the fixing heaters have been turned on for warming up. • The fixing temperature remains below 50C/122F for 10 s continuously after the fixing heaters have been turned on during stabilization.
• Causes: Poor contact of the fixing unit thermistor connector terminals. Broken fixing unit thermistor wire. Fixing unit thermistor installed incorrectly. Fixing unit thermostat triggered. Fixing unit heater M or S installed incorrectly. Broken fixing unit heater M or S wire.
• Remedy: Check the connection of connector CN3-B8 on the engine PCB and the continuity across the connector terminals. Repair or replace if necessary. Measure the resistance. If it is infinite, replace the fixing unit thermistor. Check and reinstall if necessary. Check for continuity. If none, replace the fixing unit thermostat. Check and reinstall if necessary. Check for continuity. If none, replace the fixing unit heater M or S.

• Code: C620
• Description: Abnormally low fixing temperature • The fixing temperature remains below 120C/248F for 10 s.
• Causes: Poor contact of the fixing unit thermistor connector terminals. Broken fixing unit thermistor wire. Fixing unit thermistor installed incorrectly. Fixing unit thermostat triggered. Fixing unit heater M or S installed incorrectly. Broken fixing unit heater M or S wire.
• Remedy: Check the connection of connector CN3-B8 on the engine PCB and the continuity across the connector terminals. Repair or replace if necessary. Measure the resistance. If it is infinite, replace the fixing unit thermistor. Check and reinstall if necessary. Check for continuity. If none, replace the fixing unit thermostat. Check and reinstall if necessary. Check for continuity. If none, replace the fixing unit heater M or S.

• Code: C630
• Description: Abnormally high fixing temperature • The fixing temperature exceeds 220C/428F for 10 s. • The fixing unit high temperature detection circuit on the engine PCB detects an abnormally high temperature.
• Causes: Shorted fixing unit thermistor. Broken fixing unit heater control circuit on the power source PCB.
• Remedy: Measure the resistance. If it is infinite, replace the fixing unit thermistor. Replace the power source PCB.

• Code: C640
• Description: Zero-crossing signal problem • The main PCB does not detect the zero-crossing signal (Z CROSS SIG) for the time specified below. At power-on: 3 s Others: 5 s
• Causes: Poor contact of the connector terminals. Defective power source PCB. Defective main PCB.
• Remedy: Check the connection of connectors CN10-5 on the main PCB and CN4-3 on the power source PCB, and the continuity across the connector terminals. Repair or replace if necessary. Check if the zero-crossing signal is output from CN4-3 on the power source PCB. If not, replace the power source PCB. Replace the main PCB if C640 is detected while CN4-3 on the power source PCB outputs the zero-crossing signal.

• Code: C710
• Description: Toner sensor problem • The sensor output voltage is outside the range of 0.5 to 4.5 V during copying or in maintenance item U130. • The toner sensor control voltage cannot be set within the range in maintenance item U130.
• Causes: Defective toner sensor. Poor contact of the toner sensor connector terminals. Developer problem.
• Remedy: Replace the toner sensor. Reinsert the connector. Also check for continuity within the connector cable. If none, remedy or replace the cable. Replace the developer.

• Code: C730
• Description: Broken external temperature thermistor wire • The input voltage is above 4.5 V (230 bits).
• Causes: Poor contact of the humidity sensor PCB connector terminals. Defective external temperature thermistor.
• Remedy: Reinsert the connector. Also check for continuity within the connector cable. If none, remedy or replace the cable. Replace the humidity sensor PCB.

• Code: C731
• Description: Short-circuited external temperature thermistor • The input voltage is below 0.5 V (250 bits).
• Causes: Poor contact of the humidity sensor PCB connector terminals. Defective external temperature thermistor.
• Remedy: Reinsert the connector. Also check for continuity within the connector cable. If none, remedy or replace the cable. Replace the humidity sensor PCB.

• Code: C740
• Description: Toner hopper problem • The toner hopper lockup sensor does not turn off after the toner recycle motor has rotated for at least 1 minute.
• Causes: Toner main hopper lockup. Defective toner hopper lockup sensor. Poor contact of the toner hopper lockup sensor connector terminals. Defective toner recycle motor. Poor contact of the toner recycle motor connector terminals.
• Remedy: Remove the recycled toner in the toner main hopper if it locks up. Replace the toner hopper lockup sensor. Reinsert the connectors. Also check for continuity within the cable. If none, remedy or replace the cable. Check for continuity across the coils. If none, replace the recycle motor. Reinsert the connectors. Also check for continuity within the cable. If none, remedy or replace the cable.