Oki B4100 - Manual (Page 420)

40055101TH Rev.4 420 /
2) Fuser unit temperature control
The heater in the fuser unit is controlled by the thermister, IOGA3 and CPU to keep the
heater roller surface within a prescribed temperature range. The CPU supervises the status
of the port PC0 periodically, turning HEATON signal on and off according to CPU of PC0
(A/D converter input section) 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 A3.2.18 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 temperature 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.
Filter ACIN
SW1
F1
L101, R1, etc.
IC2
HEAT-N
THERM
5 V
5 V
AOUT
C4
L2
PC1
D1
1VP/2VP (Power supply unit) M17
Thermostat
Thermister
Heater
Fuser unit
CPU
IOGA
0 V
PA11
PC0
Heater
control
HEATON CN1
B7
HEAT-N
TR506
THON
65
87
THCHK A12
IC18, TR502
Figure A3.2.18 Fuser Unit Temperature Control