I downgraded AC firmware to 18.104.22.168 and RC firmware to 1.5.8 because after the latest firmware update(1.8.1.00), "No signal" happened so often during flight so that I couldn't finish a job in front of many clients. After came back home, I tried downgrading the firmware of AC/RC but when downgrading RC firmware in DJI GO app, after 99% of progress and the last long beep sound, it displayed "upgrade failed" (which means actually downgrade to 1.5.8) (My tablet is Nexus 7 2nd with Android ver.6.0.1) So, I tried a mannual update method with a USB memory stick. But nothing happened when plugged USB stick. And when I rebooted the RC, there was no booting melody with white light in the first LED on. I tried downgrading again in DJI GO app, but the same happened (at 99% with finishing beep sound and "upgrade failed" displayed) And from that time on, whenever I boot RC, the red light flickers in the first LED with strong emergency beep sound. When I get into downgrade screen of DJI GO, it goes like this: -- Firmware version: null -- No available firmware to downgrade When I click overall status, it goes like this: -- Remote controller FPGA error -- Hardware malfunction. Contact customer service for repairs. I guess this must be a firmware corruption. How can I fix this? I can't send my RC for repair because I have jobs scheduled next week. How can I initialize the RC firmware? Thanks.