Oki B4100, Maintenance Manual

Page: 401 / 637

40055101TH Rev.4
401 /
The heater in the fuser unit is controlled by the thermister, IOGA and CPU to keep the
heater roller surface within a prescribed temperature range. The CPU supervises the status
of PC0 (A/D converter input section) periodically, turning HEATON- N signal on and off
according to CPU of PC0 status to exercise temperature control.
At power on time, the CPU switches the output signal THON from pin 65 (between high
and low states) to check for a blown or shorted thermister according to the status of the
THCHK signal.
A built-in thermostat in the fuser unit prevents the heater from being overheated in event of
failures in the thermister, or temperature control circuit, etc.
Figure A3.1.16 shows the fuser unit temperature control.
Note: Heater control
Temperature of the heater at the time of printing is 150 ˚C to 180 ˚C. This tempera-
ture is maintained by controlling the on and off operation of heater according to the
input of the thermister converted into analogue-digital (A/D) values by the CPU.
2)-1 Heater control
The ACON control signal on the secondary side is transmitted to the primary side via PC3
to turn triac TRC1ON for AC voltage supply to the heater.
3) High-voltage and medium-voltage control
Figure A3.1.16 Fuser Unit Temperature Control
CPU
Heater
on/off circuit
IOGA
HEAT-N
R44
0V
0V
ACIN
F1
THCHK
5V
TRC1
AOUT
PC3
048-POW
Thermostat
Thermistor
Heater
Fuser unit
PC0
PA11
OLHV/TLHV
Board
THCHK
THON
+5V
ACON
CN7
10
CN6
13
IC2
HEATON