To enter fastboot on the Open-Q 835 HDK, follow the following steps:
- Disconnect all cables from the HDK including power
- Connect the 12V power supply to the carrier board connector J0701
- Hold down the volume down button (-) and press the "power on" button (volume down button needs to be held down while "power on" button is pressed)
- Connect a type "C" USB cable to connector J1201 on the carrier board and the other end of the type C cable to a PC
From a terminal window on the connected PC, run "fastboot devices" and see if the HDK appears in the list of connected device.
If this process fails, the bootloader is corrupted and the HDK will need to have the bootloader re-programmed. Please see here for reprogramming instructions: https://shop.intrinsyc.com/products/boot-loader-re-programming