Unable to gain access to bootloader - APM 2.0.25 Firmware Install

Hi fellow pilots,

I used to be able to connect my CX-20 to APM Planner 2 and everything worked well. Now when i try to connect there is no telemetry, so i’m trying to do an initial firmware setup again but it keeps coming up with 'Unable to gain access to bootloader’
I am running OX 10.13 High Sierra, i have installed the USB drivers. I also tried to do this via parallels on the mac with Windows10 and it come up with the same problem.

Any help would be greatly appreciated. Cheers Chris

I’ve got three CX-20 flight controllers in the box with the same symptom.They get irreversibly corrupted by the dodgy USB port on the bottom of the copter and there is no way of accessing the DFU mode to repair the bootloader.Or,I’ve never found a way to access the DFU on one of these boards.You can do it easily on a full APM 2.5/2.6 but not the cut down matchbox version fitted to the CX-20.The pins are not there and nor is the documentation.

All of my Novas (Hobbyking CX-20) now have Pixhawks and they fly a damned sight better for it.The original FC is a fun place to start but they don’t last long in my experience.

The only thing you can try is a handfull of USB leads in the hope that it didn’t yet corrupt the bootloader and it’s just the USB port.As a last resort remove the shell and hook the USB directly to the FC.

Well it’s been a very long time since you wrote these messages. However, I bought a couple of CX-20’s for ~$30/ea way back then and I’m just now getting to them. And wouldn’t you know it, when I flashed the FC it failed and the controller could not be put in to DFU mode. Well, not really, but I had to read the chip documentation to figure out how.

So this message is not just for you, but for anyone with some non-functional bricked APM v2.5.2 flight controllers.

Anyway, take the FC from the copter. Open the plastic box, and remove the ATMEGA 2560 board from the daughter board with all the connectors. Plug it into your computer with the appropriate USB cable.

Now start Mission Planner and select the firmware you want to install. Find the two pads right above the USB connector on the board, towards the center of the connector. Short them briefly. The board should be in DFU mode and you should be able to upload the firmware.