Phaser 4500/4510 Service Manual 2-25
Theory of Operation
Temperature Stabilization
The fuser automatically enters a stabilization process under two
circumstances:
■ When the printer is processing thick paper.
After 50 impressions of continuous printing on thick paper (Thick Paper 1
mode), the fuser lamp turns off, the main motor stops, and the fans rotate
at full speed until the temperature of both temperature sensors drops to
190° C or below. Then the printer continues printing the job. The process
for Thick Paper 2 is the same, except that it occurs after 30 impressions of
continuous printing on thick paper.
■ When the side fuser temperature sensor (STS) detects an abnormally
high temperature (over 245° C), the printer stops the print job and enters
the cool-down process consisting of:
■ Clearing the paper path of all paper
■ Continuing to run the main motor (Time-out 200 sec.)
■ Running the fans at full speed
■ Controlling fuser temperature with short lamp
This process continues until the target control temperature of 180° C -
185° C (Standby) is reached.
Fuser Problems (U4 Error Code)
Major causes of a U4 error include the following:
■ Warm-up failure – Fuser warm-up not complete within 110 seconds after
starting.
■ Cool-down error – Cool-down process not complete within 200 seconds.
■ Low trouble temperature – The fuser temperature drops to the low trouble
temperature (approximately current control temperature, minus
approximately 25° C).
■ High trouble temperature – The fuser temperature rises to the high trouble
temperature (approximately current control temperature, plus
approximately 35° C).
■ STS circuit open
■ STS failure – The heat rod remains on for at least 10 seconds after warm-
up has completed.
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