Use a multimeter to test that there should be two solder joints that are through, or find a chip on the board that can determine the power and ground pins, and test which solder jo...
There is a circuit board, how to distinguish the positive and negative poles without connecting to the power supply?
Use a multimeter to test that there should be two solder joints that are through, or find a chip on the board that can determine the power and ground pins, and test which solder joints are through with them, you can really be positive or negative.