1. Please replug and check again the ribbon cable connection to make sure the cable is not reversely connected.
2. If the connector between the two layers of PCB boards becomes loose, the camera won't give any response and no LED on the board will light up. Please separate the two layers of PCB boards and reconnect them carefully. And make sure below screws are screwed tightly.
3. Please remove the ribbon cable and power up the PCB separately to see if it can be turned up.
4. Please power your Split mini with a phone charger(5V 1-3A) via a USB cable. If it turns on, please check if your BEC/VTx/FC 5V supplies enough output current(Split Mini's working current is about 650mA under 5V input).
5. If this problem occurred after firmware update, please contact us via firstname.lastname@example.org for USB-style firmware update method.
6. If the problem still exists, please show us a video illustrating the situation and make sure the status of the LEDs are shown. And then disassemble the camera and take off the PCB and show us HD pictures of both sides of the two boards.