I2C using LCD Display(Nucleo)

I2C using LCD Display(Nucleo-F746ZG)
Hi here i used LCD RG1602A and I2C IC - PCF8574T

when i was Connected power supply that LCD Back light only on.
MY lcd.printf("123456789123456789\n "); not printing in the Display unit…
below Attached My code

#include "mbed.h"
#include "TextLCD.h"
Serial pc(USBTX,USBRX);  
//I2C Communication
I2C i2c_lcd(PB_9, PB_8); // SDA, SCL
TextLCD_I2C lcd(&i2c_lcd, 0x4E, TextLCD::LCD16x2, TextLCD::HD44780); // I2C bus, PCF8574 Slaveaddress, LCD Type, Device Type 

int main() 
    pc.printf("enter the main");
lcd.setMode(TextLCD::DispOn); //DispOff, DispOn
lcd.setBacklight(TextLCD::LightOff);//LightOff, LightOn
lcd.setCursor(TextLCD::CurOff_BlkOff);//CurOff_BlkOff, CurOn_BlkOff, CurOff_BlkOn, CurOn_BlkOn

    lcd.printf("123456789123456789\n ");



did you have correctly set the contrast of your LCD via pot on backside of your I2C/GPIO expander?

BR, Jan