This fault is normally caused by a Nand-flash ship loosing its programming. To confirm this check your SD card after you have tried to update it for the hiding log called LOG_AB. To find this hidden folder you will need to set your pc to show hidden files.
Once you find the Log look for these 2 errors below.
[15 00] device not detected.
[08 00] device not detected.
This fault can be normally fixed by re-flashing the chip. To do this the gimbal top board needs removed and wires soldered directly to the board from a serial programmer. This requires a high level of soldering and computer programming skills.
To get this repaired book a repair here and we will do the hard work for you.