If this happens, that means Ambarella chip is booting up, and then restarting, and then booting up again - in an endless circle.
Sometimes putting a firmware update on the card can break the loop, but in most cases the reboot happens before the drone checks for update on SD-card.
To diagnose this issue, it is required to see messages which the chip displays as it's booting. The messages can be read either by tapping to serial interface, or creating a special file on SD-card which causes them to be stored on SD-card. The messages will contain specific reason why the chip decides to reboot.
Details:
Ambarella firmware interfaces
In more basic terms: Gimbal Top Board is damaged.