So I bought a 2nd hand analog flywoo explorer and also a digital betafpv 85x digital last year.  I successfully took the caddx vista off of the 85x and got it on the flywoo.  For some reason that escapes my mind now, i put the GPS on the Soft serial port, and it all seemed to be working fine.

Well earlier this year, i decided that i was going to upgrade the GPS because the stock flywoo one is pretty terrible.  I was doing some reading and I came to the conclusion that i should move the gps to a hardware UART port and run the caddx vista off of the soft serial port.

So i do the soldering, everything goes well.  I plug the quad into my PC, open betaflight and in the ports screen i enable MSP on soft serial, and disable GPS.  I disable MSP on UART2(possible the root of my trouble) and enable GPS and set the baud rate to auto. save and reboot.

Now the quad will not connect to betaflight, but it does open the serial port succesfully.

So i know I f'd something up here, maybe the CADDx was actually connected to UART1(The only diagram im able to find of the FC is slightly different that my FC(mine doesnt seem to have the SCL and SDA ports)

but i think, no big deal, i can just flash the firmware to it, and start over.   Well, when i boot my FC in DFU mode, my computer doesnt recognize it. I get the message "Unknown USB Device (Device Descriptor Request Failed)"  Ive tried the impulsefc driver fix and zadig to change the drivers, and ive also tried manually selected the drivers using Properties>update driver>have disk> point to stmcdc.inf and it just says that those drivers arent compatible.....

I WAS able to plug in the previously mentioned meteor 85X(now analag) in DFU mode, it initially was recognized as STM32 BOOTLOADER.  I did need to use zadig to use the proper drivers, but it seems to be working fine.  THis is on my windows 11 laptop,  i also tried connected both FC's on a different Windows 10 PC. It also seems to work fine there.

Now i assume that both the STM32F405 bootloader would use the same drivers as the STM32F411, but im not sure. 
Does anyone have any suggestions for next troubleshooting steps, or should i start shopping???

thanks in advance,

Can you go to device manager and remove the USB device? It will re-discover it again and all peripherals connected to it. I've had this issue before with DFU mode not being recognized but can't remember how I fixed it exactly, sorry.

I tried too. on both my windows 10 and windows 11 machine. i tried a different usb cable just because as well.

I appreciate any and all suggestions!

I might try and get to a friends house and just use all his hardware to see if that makes any difference

Not sure if this applies in your case, but some FCs use a specific UART for USB communication. If you have a peripheral connected to that same UART and it is also powered up, it may prevent serial communication with the MCU. If your FC uses a UART for the USB comm, make sure you disconnect anything from those same uart pads.

My FC only has 2 hardware UARTS, 1 for my ELRS transmitter, and the other was supposed to be for the GPS. Do you think this would still apply???

I should unsolder the stuff from those UARTS anyways. I will report back when i get a chance to do this

thanks again for the suggestions.

You disabled MSP which basically disabled USB communication.

Hold boot button first when you connect USB or power, and check LED show its in boot mode. STM32 bootloader is universal. Should see it in Device Manager.

If 1 board works and shows bootloader in device manager, but 2nd doesnt, its not driver.

Have you tried removing the GPS and receiver from the FC and seeing whether you can connect to Betaflight and/or flash?

F4 FCs are affected by DFU hijacking, and if you have a device that is sending data (eg GPS, receiver) connected to certain pins when the MCU boots it will get stuck thinking the UART is being used for a firmware update. UART1 on any FC using the FLYWOOF411V2 Betaflight target is affected (UART1 RX is on pin A10), so if that is the FC you have try disconnecting whatever is on UART1.

https://betaflight.com/docs/wiki/archive/DFU-Hijacking

thanks for all the suggestions guys, i havent had time to play with my quad in the last few weeks, when i get a chance i will go in and remove the GPS from the uart. I disabled MSP on uart 2, so i wouldnt have thought that would have affected USB comms, but im clearly not an expert here.

i will report back when i get a chance to play around.

thx again

Thanks again for the suggestions guys.

I unsoldered my gps, which was one of the devices i initially moved. no change, but after i unsoldered the radio, I was able to boot up into DFU mode and flash a new firmware. So I think im good here.

HOWEVER,
I was at a friends house the other day, and he had another small quad that he wasnt using that has a f405 with 3 hardware uarts. Would there be any reason to swap them? It appears to be a Diatone mamba F405 mini. not sure on the ESC size, but this flywoo/goku board only has a 13amp esc, so i can imagine the esc on this diatone board is smaller than that.

Thanks everyone for the support, The technical bar for entry for this hobby is pretty high, and without helpful people out there, it would so much harder to get any of this kind of stuff figured out.

Not that it matter at this point, but that f405 is a non-starter, the first uart was/is sbus only.

Now Im just dealing with getting the betaflight OSD working. It worked once, then i moved some of the data around in betaflight and it doesnt seem to be working again....oh well, seems like thats just how this hobby goes. lol