Xerox 4400DT Service Manual - Page 439
Laser Trouble (U2 Error Code), Fuser Control, Fuser Temperature Control, Fuser Temperature Adjustment
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Laser Trouble (U2 Error Code) There are three major causes of U2 errors: 1. Warm-up failure - SOS signal intervals are longer than the READY reference value during three consecutive samplings of the SOS. The actual laser power does not equal the value set in NVRAM. 2. Laser speed too low (Down Failure) - SOS signal intervals are longer than the set Down Failure interval after completion of warm-up. The set Down Failure is a time 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 the set Overrun Failure interval after completion of warm-up. The set Overrun Failure is a time interval corresponding to 102% of the rated Laser Motor speed of rotation. Fuser Control Fuser Temperature Control To maintain the temperature of the Fuser Heat Roller at the levels required for proper operation, the Fuser uses a Thermistor to monitor the temperature on the surface of the Heat Roller. The Engine Logic Board compares that temperature with the rated temperature that is set in NVRAM, and switches the Heat Rod on or off depending on how the actual temperature differs from the rated temperature. Fuser Temperature Adjustment You can adjust the rated Fuser temperature by changing the Fuser Configuration from the Tray Setup Menu. The printer switches on the Heat Rod when the Fuser temperature falls below the current control temperature (approximately 178° C for the standard control temperature). The printer switches off the Heat Rod when the Fuser temperature rises above the current control temperature (approximately 180° C for the standard control temperature). Fuser Warm-up Power to the Heat Rod is applied at the start of printer warm-up. Warm-up is complete when the Heat Roller reaches the current control temperature. If the Fuser temperature is below 100° C at start of warm-up, then warm-up finishes when the Fuser temperature reaches "standby temperature". 8-26 Phaser 4400 Laser Printer Service Manual
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