I followed the Qualcomm guide to build Android 6 Marshmallow from source using the guide at https://developer.qualcomm.com/download/db410c/linux-android-software-build-and-installation-guide.pdf and flashed the images. But now I don’t have any HDMI output any longer. It used to work using latest Debian and the Android 5 images provided as downloads. I can adb shell into the board. What can I do to make it work?