[maxking]

Hi, I have the HK101 TV Box with s905D soc created by Foxconn. Ths OS was android 7.1.2. Please identify the part A on the photo. The pins 1 to 5 that I tested are 0v, 3.3v, 3.3v, 3.3v, 0v. I have no idea what it is. I thought the part B was TTL port. I tested the pins 1 to 4: 0, 3.3, 2.9,0 and it should be Gnd, Vcc, TX, RX but I connected with PC no result displayed. Is it possible the kernel disable the serial console? 

HK101 motherboard photo:
https://drive.google.com/open?id=1I-kGgb...gU77-uxvF7

[noggin]

Without knowing more about your box I'd assume 'A' was a TTL-level UART Serial port.  

I would start with just finding out where GND and the TX pin (i.e. data from the box, which you will connect to the RX pin of your TTL UART interface) are.  You may have to try a variety of baud rates to find the one your box uses - and will need to power cycle it to check (as the bulk of the UART output will be during boot usually?)  You may be able to work out the GND line by continuity testing (i.e. a buzz test with a multimeter) it with known GNDs on other pins or shields.

You shouldn't need to connect VCC (which will be 3.3 or 5V) 

'B' looks like an unpopulated connector position - possibly for a front panel display on a different model, or a front panel USB port?