arduino 16x2 lcd hatası

#include <LiquidCrystal.h> 
  char ch; 
  int Contrast=125; 
  // initialize the library with the numbers of the interface pins 
  LiquidCrystal lcd(12, 11, 5, 4, 3, 2); 
   
  void setup()  
  { 
    Serial.begin(9600); 
    Serial.println("LCD test with PWM contrast adjustment"); 
    pinMode(13,OUTPUT); 
    analogWrite(6,Contrast); 
    // set up the LCD's number of columns and rows:  
    lcd.begin(16, 2); 
    // Print a message to the LCD. 
    lcd.print("LCD test!!"); 
  } 
   
  void loop()  
  { 
     digitalWrite(13,LOW); 
     delay(1000); 
     digitalWrite(13,HIGH); 
    // set the cursor to column 0, line 1 
    // (note: line 1 is the second row, since counting begins with 0): 
    lcd.setCursor(0, 1); 
    // print the number of seconds since reset: 
    lcd.print(millis()/1000); 
  } 
   
  void serialEvent() 
  { 
       if (Serial.available()) 
    { 
      ch= Serial.read(); 
      if(ch=='A' && Contrast<255) 
      { 
        Contrast=Contrast+1; 
      } 
      if(ch=='B' && Contrast>0) 
      { 
        Contrast=Contrast-1; 
      } 
          if(ch=='N') 
      { 
        analogWrite(9,28836); 
      } 
         if(ch=='F') 
      { 
        analogWrite(9,0); 
      } 
      analogWrite(6,Contrast); 
      Serial.println("Current contrast"); 
      Serial.println(Contrast); 
    } 
  }