Newhaven Display Forum

Hi,
We have the NHD-C0216CIZ-FSW-FBW-3V3 in an application.  We have built over 500 units. 
The contrast on a small percentage of the 500 units is very dark. 

The contrast is controlled via software in the initialization.  Each unit has the same code, so it sends the same contrast value.  So then why are some units much darker than most? 

Is the contrast dependent on any hardware (external to the COG/LCD module) differences/tolerances?  (I ask this because we have tried replacing the LCD module on a bad unit and the contrast problem persists- suggesting the fault is not with the LCD module.  But we've only done this once, so it's not conclusive.)

FYI, here's my init code:
const char LCD16_initString1[] = {
LCD16_Comsend,
0x38,  // function
0x39,  // function
0x14,  // Internalosc,
0x78,  // Contrast,
0x56,  // Powercontrol,
0x6D,  // Followercontrol, 
};

const char LCD16_initString2[] = {
LCD16_Comsend,
0x0C,  // Displayon,
LCD16_Clear,
0x06  // Entrymode, 
};

void LCD_init(void){
   
    LCD_RST_SetVal();
    Cpu_Delay100US( 400);
    write_i2c_LCD(LCD16_initString1,sizeof(LCD16_initString1));
    Cpu_Delay100US( 400);
    write_i2c_LCD(LCD16_initString2,sizeof(LCD16_initString2));
    Cpu_Delay100US( 400);
}