Furuno GP-90 Service Manual page 5

GPS Board, GN-8091
The board is 12 discrete channel, all - in - view, L1 GPS receiver which processes GPS signal for
position fixing and for calculating speed and course of the ship.
NP board, 20P8188
The board mainly consists of a CPU, Flash ROM stored system program, Video RAM, Backup battery,
and power supply circuit. Major function of the board is;
1) Control of entire system
2) Reading key data
3) Control of input and output data
4) Storage of GPS data, waypoints and mark data
5) Graphic data processing
6) Output of display data to LCD
7) Output of log pulse (contact closure signal), if selected
8) Producing following voltages
+5 V: for digital circuit and internal beacon receiver
+12 V: for flash memory and analog circuit
–20.5 V: LCD drive voltage
210 Vac: for LCD backlight
PNL Board, 20P8148
The board consists of 18 switches, 10 LEDs used to adjust brilliance, a buzzer, and a temperature
coefficient resistor (R1). The contrast of LCD is kept constant by R1.
LCD, EW50136FDW
The LCD contrast is stabilized by temperature compensation. Decreasing temperature, for instance,
causes an increase in R1's resistance and a consequent increase in the LCD bias voltage. The NP board,
20P8188 outputs the bias voltage from pin 2 of J10. The bias is approximately –17.9 V at 25 °C in
automatic bias mode. The bias changes from –20 V to –16 V at 25 °C in manual bias mode.
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1. Circuit Description