- I had a spare display so I replaced it. It still didn't work.
- I had a spare XU4 so I moved the eMMC card to the new XU4 and tried again. STILL no function.
- I replaced the HDMI cable. No function.
- I moved the display to a separate power supply (instead of being powered from the XU4 USB). Still no function.
- I reflashed the eMMC. Still no function.
The touchscreen has power. It has its own power LED and every time I touch the screen the power LED dims.
Is it possible the display's brightness is turned down so low that I can't see it? I don't see how 2 XU4s and 2 displays could have exact same symptoms unless something was askew with the Android image. That is the only thing they have in common.