Lexmark 43J2200 - Optra S 1620 B/W Laser Printer, Service Manual

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Diagnostic Aids
3-28
4059-XXX
the hot roll increases. The thermistor resistance changes from
approximately 150K ohms to approximately 260K ohms as the
temperature of the fuser hot roll increases. The thermistor is
connected to the fuser control board connector J2-1 and J2-2 and
from J2 to J1-2 and J1-3 on the fuser control board to J2-6 and J2-7
on the engine board. J2-6 () and J2-7 (TEMPIN-) are
connected to module PLCC U9. U9 monitors the change in
thermistor resistance and sends a signal (HEATON) from J20-A25
through the interconnect board to CN3-9 on the LVPS to signal the
triac to turn the fuser lamp On or Off to maintain the correct fuser
temperature.
The voltage drop across the thermistor is proportional to the fuser
temperature and varies from approximately 2.0 V dc (cold) to 2.3 V
dc (warm during idle) to approximately 2.7 V dc during continuous
printing. These voltages are assuming the fuser temperature is set
to normal. The HEATON signal from CN3-9 varies from 0 V dc (lamp
On) to +5 V dc (lamp Off) and is connected to the cathode of an
Opto triac to control the fuser lamp. The second part of the assembly
is the fuser frame which contains the hot roll, backup roll, and
associated parts as well as the paper exit guide assembly, narrow
media sensor, fuser control board (which has the exit sensor
mounted on the board) and the envelope conditioner solenoid on the
model 2420, 2450, 2455, 3455, 1620, 1625, 1650 and 1855.
The model 2420, 2450 and 2455 printer fuser temperature is 200.8
degrees C while printing at 600 dpi and 163.9 degrees C while
printing at 1200 dpi.
The model 1620, 1625 and 1650 printer fuser temperature is 185.5
degrees C while printing at 600 dpi and 145.5 degrees C while
printing at 1200 dpi.
The model 1250 and 1255 printer fuser temperature is 206.9
degrees C while printing at 600 dpi and 151.5 degrees C while
printing at 1200 dpi.
The model 3455 printer fuser temperature is 270 degrees C while
printing at 600 dpi and 170 degrees C while printing at 1200 dpi.