still: maybe on the other board the contrast voltage is provided in another way?
I'd double-check the contrast voltage, and rhe way it is provided.
if i connect the screen to pins 2 and 3, the screen works normally (just testing with a "hello world" for now, i can edit the text and it shows properly) it's just i already have those pins used by the controller's switches and i don't know if i can edit the code so the screen uses pins 0 and 13 for example (those are the ones i have free at the moment).
EDIT: i ended up changing the controller pins to 0 and 13 and editing the code, not sure if the 2 and 3 pins as SCL and SDA are hardcoded, time to start trying to understand how nrpn works