Oki B 4100 Maintenance Manual page 401

Facsimile transceiver

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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

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.

High-voltage and medium-voltage control

40055101TH Rev.4

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.

Figure A3.1.16 Fuser Unit Temperature Control

on/off circuit

Troubleshooting