Hi,
I bought an A20-OLinuXino-Lime board. I was wondering if there is any test I can do to find out whether the board is working other than connecting to a screen.
The most basic test if anything is working at all is to download the latest official image to an SD card, plug it in, power the board and check if the user LED starts blinking. If it does - kernel works.
Aside from that we usually use USB-serial cable to connect between the board and a personal computer. This requires 3.3V USB-serial cable with free leads, and you connect them to the RX,TX and GND pins at UART0 header. You open a serial terminal on the port created by the USB-serial cable, insert the SD card, and power the board. Boot should start and you should have access to the command line interface.
Something like this cable: https://www.olimex.com/Products/Components/Cables/USB-Serial-Cable/USB-Serial-Cable-F/