I think I'm probably also going to move my GPS module to another UART when I next have the top plate off my quad because I don't really like unnecessarily unplugging and re-plugging connectors as it can put a strain on them and wear them out / damage them for no good reason.

(30-Aug-2021, 07:47 AM)Zanna83 Wrote: Ok, the DFU issue is solved!

Yesterday I desoldered the "5V" wire of CRSF from the flight controller. As soon as no devices were connected to UARTS the FC entered DFU mode with the "press the button and plug the cable" method. I've been able to flash Betaflight again over Emuflight.

Regarding the suggestion of avoiding to desolder any cable and put the CRSF in binding mode.... it does not work.

Thx - that worked on my Goku F745 on my LR4.  And it makes sense - the GPS is on 5v, so won't turn on with the USB.  And my Vista is on 4s, so same thing.  Leaving only the CRSF Rx - on 4.5v, which is USB power - so when I pulled the Rx power - the F745 went into DFU mode immediately - and now I'm on BF4.3.0-RC2 - rather than the factory installed BF4.2.0.

(03-Sep-2021, 11:47 PM)SnowLeopardFPV Wrote: So I'm back home now and I just tested DFU mode with my GPS module connected to UART3 on my Kakute F7 HDV FC.

Nada. Unable to get into DFU mode. I unplugged the GPS module and I was then able to get into DFU mode no problem.

I did some further research and discovered that it is specifically UART1 and UART3 that causes this issue on F4, F7, and H7 FC's. So the takeaway from this is not to connect any peripherals to UART1 or UART3 on a F4/F7/H7 flight controller that power themselves up when a USB cable is connected to the FC, or if you do, make sure it's a peripheral that is connected via a plug so you can temporarily just unplug it if you need to get into DFU mode.

I have a JHEMCU GHF420AIO which came loaded with Betaflight 4.2.0. I'm running BF version 4.2.11 on all my quads (waiting for the 4.3 official release) and so I wanted to flash my flight controller.  I tried everything under the sun but I could NOT get it to boot into DFU mode. Then I found this older post by SnowLeopardFPV and considered that I had connected my TBS Crossfire Nano Rx to TX1/RX1 (UART1).  With nothing to loose, I desoldered the 5V power to the receiver and, violia, I got into STM32 Bootloader with no problem. I've never heard of this issue before but I'm guessing that all manufacturers just know to avoid UART1 and UART3 for precisely this reason.

Thank you very much!