nokia 5110 display

Hi ! I have a nokia 5110 display with 8 pins , one of witch is GND . I've connected all pins to my nano, and all works perfectly....but if I disconnect the GND pin from the board , all works perfectly so .
Why the GND pin exist ?? / What's its role/function/sense ?

Reconnect the ground before you damage the device.

With no GND connection, all of the supply current, LED backlight included, is most likely passing through an input pin being held low, either the RST or SCE pin. The return path current is going somewhere, enough to power the device but that does not mean it will continue to function correctly.

This behavior is not uncommon for a low current CMOS device. But, it does not be mean you can leave grounds disconnected. You managed to learn something with hopefully not having permanently damaging the part.

MoRommy:
Hi ! I have a nokia 5110 display with 8 pins , one of witch is GND . I've connected all pins to my nano, and all works perfectly....but if I disconnect the GND pin from the board , all works perfectly so .
Why the GND pin exist ?? / What's its role/function/sense ?

As has been mentioned the 5110 is a low current device, it might work without the GND pin, but do not use it like that.

And out of interest why were you disconnecting pins in the first place on a working device?

That sort of tactic is defientely not recommended and can get expensive.

ok..i understand. Thanks a lot all !