Engine Controller - Xerox WorkCentre Pro 412 Service Manual

Circuit Description

5-5 Engine Controller

5-5-1. Fuser Control / Thermistor Circuit
This circuit controls the heat lamp temperature to fix the transferred toner on the paper. It is comprised of the
thermistor that has the negative resistance against the temperature and LM393 (voltage comparator) and
transistor for switching.
The thermistor has the resistance value reverse proportional to the heat lamp surface temperature. The volt-
age value is read by #60 pin(AVIN2) of CPU referring to the parallel combined resistance with the resis-
tor(R43) connected parallel to it and the voltage distribution of R29. The voltage read activates (inactivates)
'fuser' signal to high (or low) referring to the set temperature and when the 'FUSERON' signal turns down
(high) to low (high) by Q3 switching, the S21ME4 inside SMPS (PC3) turns on (off) and this eventually turns
two-way thyristor(THY501) on (off) to allow (shut) AC voltage to the heat lamp.
LM393 is hardware designed to protect the system when the firmware that controls the heat lamp no longer
functions correctly. When the thermistor temperature goes beyond 210 degrees C, the level of pin #1
(LM393) will turn low, which turns the 'FUSERON' signal to high. The LM393 will force the heat lamp off by
forcefully shutting off the power to Q3.
5-5-2. Paper Sensing Circuit
1) Cover Open Sensing
Cover open sensor is located on the right side of the printer. In case the right cover is open, it shuts +5V
(LSU laser unit) and +24V(main motor, polygon motor of fixer LSU and HVPS) that are supplied to
each unit. It detects the cover opening through CPU. In this case, the red LED of the OP panel
LED will turn on.
2) Paper Empty Sensing
The paper empty sensor (photo interruptor), located inside bottom of the bin cassette detects paper with
the actuator connected to it and informs the CPU of whether there is paper. When there is no paper in
the cassette, the red LED of the OP panel LED will turn on to tell the user to fill the cassette with paper.
3) Paper Feeding
When the paper is fed into the set and passes through the actuator of the feed sensor unit, transistor
inside the photo interrupter will turn on, 'nFEED' signal will turn low and inform CPU that the paper is
currently fed into the system. CPU detects this signal and sprays video data after certain time (related
to paper adjustment). If the paper does not hit the feed sensor within certain time, CPU detects this and
informs as "Paper Jam0" (red LEDs on the OP panel will turn on).
4) Paper Exit Sensing
The system detects the paper going out of the set with the exit sensor assembled to the actuator
attached to the frame. If CPU does not turn back high a while after the paper hits the exit sensor, CPU
detects this and inform as "Paper Jam2" (red LEDs on the OP panel will turn on).
5-26
August 2001
WorkCentre Pro 412
Launch Issue