Try the SD card image from Bitmain you can find it here https://service.bitmain.com/support/download?product=Flashing%20SD%20card%20with%20image

I do not know if it can disable signature check but try it first.
If it doesn't work try the firmware provided from this link below

- https://bitcointalk.org/index.php?topic=5253966.0

Then flash it again with HiveOS. Let see if it will work.