GLCD KS0107 issue


I have a problem with my GLCD KS0107, I connected it to my arduino like in the new GLCD beta library, but nothing is displayed.
It’s well connected, I checked several times.

In the library doc it’s written

?Check contrast voltage (typically between -3 and -4 volts) on contrast-in pin of LCD
panel. While the sketch is operating, try gradually adjusting the pot through its range.
Some displays are very sensitive to this setting.

this pin is regulated by a potentiometer which is connected between grd and pin 18 (contrast out). But when I take the voltage, pin 18 is at -1.33V, so I can’t give a voltage between -3 and -4V.

You don’t know if it’s the problem. Have you got an idea ?