Revsearcher

Thank you very much all.
I could install armbian; the problem was related to the HDMI issue that doesn't work on my device, and the led keep red.
The interesting part is that I bought the device as a 4gb ram (and android shows 4gb) while it only has 1.5GB when I checked by armbian!
I also took another image with a higher quality might be useful:

It is almost impossible to remove the heatsink, but as I checked carefully I could see the bga pins only.
Thanks. You solved my problem. I checked all the SD-card/USBs and Ethernet pins for the UART part, but I couldn't get any result.

@Revsearcher
Try to remove heatsink the uart could be there

@Revsearcher that's a completely new board and it looks like this is the first board with eMCP on rk3318 to me.
Indeed the serial log would be very useful, but I see the serial is buried somewhere and not immediately accessible.
I will take a look to the dtb...
 
Ah, the photos are quite low resolution, I can't read anything on the board and neither the chip details are readable...

@Revsearcher Also look under the green quality test sticker on the under side if some pads is being hidden there.
You have 2 pads on the upper side hear the unpopulated ram / MMC pads that very likely is forcing mask rom mode but cant being 100% sure if not tested with high impedance  resistor shutting them or oscilloscope. 
 
I think its one RL3318 box that is super stripped like my and many other RK3228A boxes and the HDMI is not working with armbian then have doing no standard layout of the PCB and need patching the RK chip for getting it working that we dont knowing for the moment. If its so you shall getting the Ethernet requesting one IP-address if waiting some minute with multi too and can connecting with SSH to it but then is normally the LED looking OK.
Some PB is using the SD-card pins for UART if no SD-card is inserted but i think its not supported for all PCBs (its using 2 pin serial = UART if not card is in and 4 pin serial then card is inserted and loading the MMC module for the SD-card).