1. Check if the golden fingers on the two ends of ribbon cable are inserted correctly. Please refer the following FAQ CAREFULLY:
How replace lens cable of Split?
2. Please try to power up the Split via USB by a phone charger (5V 1-3A) to see if it will work properly. If it works, it means your PDB / BEC / FC / VTx can't supply enough current to Split. The average working current of Split Mini is about 650mA. So please make sure the input current is enough for it to work normally. It is better to power your Split via dedicated BEC(5V >=1A) / PDB(5V >=1A)/ FC(5V >=1A).