Finally I got the necessary HDMI cable to see what’s going on…
The device actually boots after installing the 4.x kernel.
What is not working is the network…
I’ve found this github issue: https://github.com/Fourdee/DietPi/issues/899
System boots, no ethernet. dmesg | grep eth = usbcore: registered new interface driver cdc_ether
Thanks to Meveric for heads up, dtb’s for XU3/4 4.9 kernel are now unique.If XU4 board:
sed -i “s#exynos5422-odroidxu3.dtb#exynos5422-odroidxu4.dtb#g” /DietPi/boot.ini
I’ve tried to exchange the 3 to 4 in the /boot/boot.ini file. This didn’t work after looking
into the file again after the next reboot. Obviously the /boot/boot.ini file is autogenerated
(every time)? from /DietPi/boot.ini
After exchanging the value in that file, rebooting…
Finally, the device booted with the correct .dtb file and the network is found again.
Problem solved 