• Code: 6400
• Description: Zero-cross signal error
  The zero-cross signal does not reach the engine PWB for more than 1 s.
• Causes: Defective connector cable or poor contact in the connector. Defective power source PWB or engine PWB.
• Remedy: Defective connector cable or poor contact in the connector. Reinsert the connector. Also check for continuity within the connector cable. If none, replace the cable. Power source PWB (YC103) and relay PWB (YC1) Relay PWB (YC4) and engine PWB (YC9)
  Defective power source PWB or engine PWB. Replace the power source PWB or the engine PWB and check for correct operation.

• Code: 7001
• Description: Toner motor K error
  When the toner motor K is driven, the motor over-current detection signal is detected continuously for 50 times (5 s) at 100 ms intervals.
• Causes: Defective connector cable or poor contact in the connector. Defective drive transmission system of the toner motor K. Defective toner motor K. Defective engine PWB.
• Remedy: Defective connector cable or poor contact in the connector. Reinsert the connector. Also check for continuity within the connector cable. If none, replace the cable. Toner motor K and engine PWB (YC23)
  Defective drive transmission system of the toner motor K. Check if the rollers and gears rotate smoothly. If not, grease the bushes and gears. Check for broken gears and replace if any.
  Defective toner motor K. Replace the toner motor K.
  Defective engine PWB. Replace the engine PWB and check for correct operation.

• Code: 7002
• Description: Toner motor C error
  When the toner motor C is driven, the motor over-current detection signal is detected continuously for 50 times (5 s) at 100 ms intervals.
• Causes: Defective connector cable or poor contact in the connector. Defective drive transmission system of the toner motor C. Defective toner motor C. Defective engine PWB.
• Remedy: Defective connector cable or poor contact in the connector. Reinsert the connector. Also check for continuity within the connector cable. If none, replace the cable. Toner motor C and engine PWB (YC25)
  Defective drive transmission system of the toner motor C. Check if the rollers and gears rotate smoothly. If not, grease the bushes and gears. Check for broken gears and replace if any.
  Defective toner motor C. Replace the toner motor C.
  Defective engine PWB. Replace the engine PWB and check for correct operation.

• Code: 7003
• Description: Toner motor M error
  When the toner motor M is driven, the motor over-current detection signal is detected continuously for 50 times (5 s) at 100 ms intervals.
• Causes: Defective connector cable or poor contact in the connector. Defective drive transmission system of the toner motor M. Defective toner motor M. Defective engine PWB.
• Remedy: Defective connector cable or poor contact in the connector. Reinsert the connector. Also check for continuity within the connector cable. If none, replace the cable. Toner motor M and engine PWB (YC24)
  Defective drive transmission system of the toner motor M. Check if the rollers and gears rotate smoothly. If not, grease the bushes and gears. Check for broken gears and replace if any.
  Defective toner motor M. Replace the toner motor M.
  Defective engine PWB. Replace the engine PWB and check for correct operation.

• Code: 7004
• Description: Toner motor Y error
  When the toner motor Y is driven, the motor over-current detection signal is detected continuously for 50 times (5 s) at 100 ms intervals.
• Causes: Defective connector cable or poor contact in the connector. Defective drive transmission system of the toner motor Y. Defective toner motor Y. Defective engine PWB.
• Remedy: Defective connector cable or poor contact in the connector. Reinsert the connector. Also check for continuity within the connector cable. If none, replace the cable. Toner motor Y and engine PWB (YC26)
  Defective drive transmission system of the toner motor Y. Check if the rollers and gears rotate smoothly. If not, grease the bushes and gears. Check for broken gears and replace if any.
  Defective toner motor Y. Replace the toner motor Y.
  Defective engine PWB. Replace the engine PWB and check for correct operation.

• Code: 7401
• Description: Developing unit K noninstalling error
  No density detection signal is output from toner sensor K in developing unit K.
• Causes: Defective connector cable or poor contact in the connector. Defective toner sensor K. Defective engine PWB.
• Remedy: Defective connector cable or poor contact in the connector. Reinsert the connector. Also check for continuity within the connector cable. If none, replace the cable. Developing unit K and Drum relay PWB (YC6) Drum relay PWB (YC1) and engine PWB (YC34)
  Defective toner sensor K. Replace the developing unit K.
  Defective engine PWB. Replace the engine PWB and check for correct operation.

• Code: 7402
• Description: Developing unit C noninstalling error
  No density detection signal is output from toner sensor C in developing unit C.
• Causes: Defective connector cable or poor contact in the connector. Defective toner sensor C. Defective engine PWB.
• Remedy: Defective connector cable or poor contact in the connector. Reinsert the connector. Also check for continuity within the connector cable. If none, replace the cable. Developing unit C and Drum relay PWB (YC10) Drum relay PWB (YC1) and engine PWB (YC34)
  Defective toner sensor C. Replace the developing unit C.
  Defective engine PWB. Replace the engine PWB and check for correct operation.

• Code: 7403
• Description: Developing unit M noninstalling error
  No density detection signal is output from toner sensor M in developing unit M.
• Causes: Defective connector cable or poor contact in the connector. Defective toner sensor M. Defective engine PWB.
• Remedy: Defective connector cable or poor contact in the connector. Reinsert the connector. Also check for continuity within the connector cable. If none, replace the cable. Developing unit M and Drum relay PWB (YC7) Drum relay PWB (YC1) and engine PWB (YC34)
  Defective toner sensor M. Replace the developing unit M.
  Defective engine PWB. Replace the engine PWB and check for correct operation.