Samsung SCX-5315F Service Manual page 147

3-5 Engine Controller
3-5-1. 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 refering 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(SY1) on(off) to allow(shut) AC voltage to the heat lamp.
LM393 is a H/W designed to protect the system when the software heat lamp control does not run normal.
When the thermistor temperature goes up to 210°C, #1 pin's level (LM393) will turn low to turn the 'fuseron'
signal to high. (forcefully shuts off Q3)In other words LM393 shuts off the heat lamp forcefully.
3-5-2. Paper Sensing Circuit
1) Cover Open Sensing
Cover Open Sensor is located on the right rear 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 papers.
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 LED 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).
Samsung Electronics
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Circuit Description
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