Problems with 'Robot LCD' board

Hello!

Recently I acquired a Robot LCD board (A000096) to use with either my Uno R3 or Mega 2560. Bought it as a genuine product. I've tried to install it however even the basic functions won't work. The screen lights up but shows no data or anything. Just bare backlight.

Both the Uno and the Mega do not get the screen to work. I have tried several example codes, including https://www.arduino.cc/en/Tutorial/TFTDisplayText and https://www.arduino.cc/en/Tutorial/TFTPong

Just to be sure, I installed a 4k7 pull-up resistor on CS SD. Also added a LED on the MOSI pin (with a 1kOhm resistor) which shows some action. It lights up and flashes off every +- 250ms. At last, a LED on the MISO pin, however this one does not blink at all! It stays off.

Current code for the Mega:

#include <TFT.h>  // Arduino LCD library
#include <spi.h>

// pin definition
#define cs   3
#define dc   5
#define rst  4



// create an instance of the library
TFT TFTscreen = TFT(cs, dc, rst);

int backlightPin = 6;
int val = 127;
// char array to print to the screen
char sensorPrintout[4];

void setup() {

  pinMode(backlightPin, OUTPUT);
  
  Serial.begin(9600);
  // Put this line at the beginning of every sketch that uses the GLCD:
  TFTscreen.begin();

  // clear the screen with a black background
  TFTscreen.background(0, 0, 0);

  // write the static text to the screen
  // set the font color to white
  TFTscreen.stroke(255, 255, 255);
  // set the font size
  TFTscreen.setTextSize(2);
  // write the text to the top left corner of the screen
  TFTscreen.text("Sensor Value :\n ", 0, 0);
  // ste the font size very large for the loop
  TFTscreen.setTextSize(5);
}

void loop() {

  digitalWrite(backlightPin, val / 4);
 
  // Read the value of the sensor on A0
  String sensorVal = String(analogRead(A0));

  // convert the reading to a char array
  sensorVal.toCharArray(sensorPrintout, 4);

  Serial.println(sensorPrintout);

  // set the font color
  TFTscreen.stroke(255, 255, 255);
  // print the sensor value
  TFTscreen.text(sensorPrintout, 0, 20);
  // wait for a moment
  delay(500);
  // erase the text you just wrote
  TFTscreen.stroke(0, 0, 0);
  TFTscreen.text(sensorPrintout, 0, 20);
}

Could anyone help me out?