If you are experiencing a black screen when plugging in the device to a monitor and it shows no signal from the HDMI input, please read on:
The MicroHDMI port in the RX420(HDX), due to mechanical specifications, requires that a MicroHDMI connector is inserted all the way into the port.
The issue described in this article is present when the MicroHDMI connector looks like it is correctly plugged in, but a small gap remains, therefore not allowing pins within such connector to make proper contact with the port. Keep in mind that this is a sensitive contact.
In such case, gently, put pressure to push further the MicroHDMI connector into the MicroHDMI port of the RX420(HDX). it should not feel loose or wiggle in any direction once it is firmly inserted.