https://learn.pi-supply.com/make/gert-vga-666-assembly-tips-and-gotchas/

On the command edit:

 $ sudo nano /boot/config.txt

Then add these lines at the bottom of the file:

 dtoverlay=vga666
 enable_dpi_lcd=1
 display_default_lcd=1

You also need to specify your screen resolution. After the lines you added above you will also have to then add one of the following configurations:

 #For 1920x1080 60Hz
 dpi_group=2
 dpi_mode=82
 
 #For 1280x1024 60Hz
 dpi_group=2
 dpi_mode=35
 
 #For 1024x768 60Hz
 dpi_group=2
 dpi_mode=16
  
 #For 800x600 60Hz
 dpi_group=2
 dpi_mode=9

Xou will need SPI and I2C to be disabled. Verify that by looking in the config.txt for the following two lines:

 dtparam=spi=off
 dtparam=i2c_arm=off 

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