Easy way to find RX TX pinout beginner tricks special for china phone

Disassemble the phone and check PCB for the RX TX points..

If you not found a RX TX on PCB you have to check voltages on USB connecter for find the RX,TX. check this example.

Explain to find pinout on 12 pin usb connector.

1. At first, you need to find GND signal (3pin-00.2v)

2. The second step: you need to find Tx Rx signals. Choose the pinouts, that may probably suit. You have 12 pinouts:

1pin-0.00v - this pinout is wrong

2pin-2.78 - it may correspond to Tx Rx signals
3pin-00.2v - GND signal
4pin-2.75v - it may correspond to Tx Rx signals
5pin-1.09v - LOOKS LIKE Tx Rx signals, BUT IT IS NOT!
6pin-0.00v - this pinout is wrong
7pin-4.02v - this pinout is wrong
8pin-2.89v - it may correspond to Tx Rx signals
9pin-3.05v - this pinout is wrong
10pin-0.00v - this pinout is wrong
11pin-1.09v - it may correspond to Tx Rx signals
12pin-0.02v - YOU DON'T NEED these fake signals with high and low voltage

3. In order to find Tx you need to put multimeter to test, diod ( "+" and "-" = beep ).

When the phone is POWERED ON, Tx with GND make a sound beep.
When it is TURNED OFF, it shows 600-700 ohm.

It is suggested to do all the job using wire connection.

After following the above mentioned steps you'll find, that 2pin is Tx and 8pin is Rx. Tx has to be 1.7v or 2.7v and Rx - 1.8v or 2.8v. These characteristics may change depending on the processor parameters. But Tx and Rx is not the same. Tx can be 2.78v, 2.75v, 2.7v.