8-26 Phaser 4400 Laser Printer Service ManualLaser Trouble (U2 Error Code)There are three major causes of U2 errors:1. Warm-up failure - SOS signal intervals are longer than the READY referencevalue during three consecutive samplings of the SOS. The actual laser power doesnot equal the value set in NVRAM.2. Laser speed too low (Down Failure) - SOS signal intervals are longer than the setDown Failure interval after completion of warm-up. The set Down Failure is atime interval corresponding to 90% of the rated Laser Motor speed of rotation.3. Laser speed too high (Overrun Failure) - SOS signal intervals are shorter than theset Overrun Failure interval after completion of warm-up. The set Overrun Failureis a time interval corresponding to 102% of the rated Laser Motor speed ofrotation.Fuser ControlFuser Temperature ControlTo maintain the temperature of the Fuser Heat Roller at the levels required for properoperation, the Fuser uses a Thermistor to monitor the temperature on the surface ofthe Heat Roller. The Engine Logic Board compares that temperature with the ratedtemperature that is set in NVRAM, and switches the Heat Rod on or off depending onhow the actual temperature differs from the rated temperature.Fuser Temperature AdjustmentYou can adjust the rated Fuser temperature by changing the Fuser Configuration fromthe Tray Setup Menu.The printer switches on the Heat Rod when the Fuser temperature falls below thecurrent control temperature (approximately 178° C for the standard controltemperature). The printer switches off the Heat Rod when the Fuser temperature risesabove the current control temperature (approximately 180° C for the standard controltemperature).Fuser Warm-upPower to the Heat Rod is applied at the start of printer warm-up. Warm-up iscomplete when the Heat Roller reaches the current control temperature. If the Fusertemperature is below 100° C at start of warm-up, then warm-up finishes when theFuser temperature reaches ìstandby temperatureî.
