get the airos fw that will flash from tftp, power it up while holding reset button for cca 8 sec. (sometimes this fails, just try more than once until you get ping replies from 192.168.1.20).
tftp the file and wait until device restart and boots. i was able to recover litebeam this way on several occasions and discovered simple method for upgrading to openwrt: Ubiquiti making it increasingly difficult to install LEDE on Unifi hardware