Sharp AR-650 Manual de servicio descargar pdf (Pagina 263)

FUSER UNIT 14 - 6

R165

R170

R174

C125

HTRTH-

Thermistor-1

Main

Processor

14.4.2 Detection of thermistor burnout

* Since thermistor burnout detection circuits of the thermistor-1 and -2 are common, it is explained with

the thermistor-1.

• The input voltage is obtained by voltage dividing

R165, thermistor, R170 and R174.

• The surface temperature of the heat roller

changes.

→ The thermistor resistance value changes

→ The input voltage also changes

• The main processor detects an abnormality

→ thermistor broken

14.4.3 Control for abnormal heater condition

When something abnormal occurs in the heater turn-ON circuit, such as a shorted triac, it may become

incapable of ON/OFF control. In this case, the microcomputer detects abnormal temperatures through

the first and second thermistors, determines the corresponding error codes and counter values, and

causes the main power to switch OFF to protect the fuser unit.

(1) Temperature detection

The following abnormal temperatures are detected by the respective thermistors:

First thermistor: 230°C

Second thermistor:270°C

(2) Error codes

“C44” : Displayed when keys C + 8 are pressed simultaneously at the time of Call

Service.

Counter value “9”: Displayed when you input “400” in the setting mode.

(3) Machine condition

After de-energizing all outputs (heater lamp, exposure lamp, control-panel displays, motors, etc.), the

microcomputer causes the main power to switch OFF.

(4) Corrective action

After the error code and counter value in (2) have been determined, abnormal temperature detection

in (1) continues. So, if the main switch is turned ON immediately, it will be turned OFF again as long

as the temperature on the heater surface remains above the abnormal detection temperatures of

thermistors. Thereafter, this will be repeated. So, after waiting for the heater surface temperature to

drop, turn ON the main switch and you can check the counter value before the main switch is turned

OFF again. After confirming that an abnormal heater condition has occurred, repair the problem and

then clear code 400 of the setting mode with “0”. After that, you can bring the copier into its normal

operating condition.

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Sharp AR-650 Manual de servicio Pagina 263

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