Automatic Control Of Lcd Contrast - Canon NP6251 Service Manual

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CHAPTER 7 EXTERNALS/AUXILIARY MECHANISMS

3. Automatic Control of LCD Contrast

The control panel controller PCB is equipped with a mechanism capable of

automatically adjusting the LCD contrast according to changes in temperature.

A thermistor (TH911) is mounted on the control panel controller PCB to monitor the

temperature inside the control panel unit. The changes in the resistance of the thermistor

caused by changes in temperature are used to vary the voltage supplied to the LCD

assembly to maintain a specific contrast of the LCD display at all times.

The LCD contrast remains constant free of the influence of ambient temperature

once it is set by the contrast adjusting knob on the control panel.

If the temperature around the control panel rises, the resistance of the thermistor will

lower, thereby increasing the voltage (Vo) supplied to the LCD unit.

If the temperature around the control panel lowers, on the other hand, the resistance

of the thermistor rises, thereby decreasing the voltage (Vo) supplied to the LCD unit.

Vo: Voltage supplied to LCD unit

Figure 7-103

CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)

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