Passport 2 Passive Display/Keypad Interface Board Theory of Operation
2 - 42 0070-10-0441 Passport 2®/Passport 2 LT™ Service Manual
LCDBIAS Control Circuit
In order to properly turn on the passive display, the board employs a N-Channel FET which is
switched on and off by the LCDBIAS signal from the CPU board. The LCDBIAS signal is
connected to the CPLD for power sequencing. The contrast function is accomplished by
varying a 10K potentiometer.
LCDADJ Control Circuit
The contrast function is accomplished by varying a 10K potentiometer.
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