The best indicator is the green / blue light (different depending on the version) LED on the HDMI board (the board closest to the UV light, see photo below). Here is a description and possible causes ...
lcd
LCD is showing a split image or ghosting
The LCD module is very fragile and many units have been delivered with the LCD damaged during shipping. Check this page for photos and suggestions. The newest D7 units are now shipping with an acrylic...
LCD does not show anything and there is a blinking light on the HDMI board
When the light on the HDMI board is blinking that means the board is not receiving any signal from the computer (or RaspberryPi). Check that the HDMI cable is connected securely Check that the PC is s...
I can not update the I3 Plus LCD Firmware to update the latest version
Your suggestion did the trick. I first tried to downgrade the LCD to 2.16 – which failed the same way (flashing LCD, no loading of images). However, when I tried to upgrade to LCD 2.17, it l...