Need help to find serial port on hi3536 board

[gianrubio]

I recently bought this Chinese [1] nvr board with chipset hi3536, model nbd8004-r fw v2.01. I’ve been trying to find the serial ports on this device but no lucky yet. The serial port does not show any data. The same USB adapter works fine to connect to a raspberry over serial, so I don’t think it’s the culprit.



The board with the welded jumpers

The data sheets points the serial port to the connector that I welded. The voltmeter read the following voltages: 2.4v, 3.3v and gnd, from left to right.

I’ve tried all the jumper combinations possibilities but none had worked.

I could not find the original datasheet for the same board, this one is pretty similar though

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[gianrubio]

 

[VorlonFrog]

Approach it logically (apologies if this is what you've already done!)

1. Identify GROUND / GND pin of the three pins, using continuity/resistance on your digital multi-meter.
If Ground isn't properly connected, NOTHING will work.

2. Identify TRX/TXD/TX Transmit Data pin.
Connect RXD pin of your USB to either of the two remaining pins, and apply power to the board.
The board should output a minimum of some text/lines during startup.
If the first attempt fails, try the remaining pin.
Remember to remove and re-apply power AFTER connecting to the remaining pin.

3. If NEITHER pin provides any kind of output, check your USB serial port settings:
115200 BAUD / BPS
8-bit characters
1 stop bit
Retry Step 2, if still nothing, try 38400 and/or 19200 and/or 9600 BAUD / BPS values

4. If you finally get intelligible output from the board, then connect the one remaining pin.
It should be RCV/RXD/RX Receive Data pin.
It should connect to the TRX/TXD/TX Transmit Data pin on your USB.

Good Luck!!


Oh, one other wild-ass suggestion:
If you have a second USB/Serial cable, try plugging it into the USB port on the board.
You'd be amazed, they often code the boostrap to use TTYAMA1, or TTYAMA2, just to confound most people.