Hi all. I recently bought an STM32F103 board from ebay (standard blue pill type).
I understand the 10k resistor on R10 (103 type) needs to be replaced ny 1 1.5K resistor for the USB to work. I dont have a 1.5K SMD resistor at the moment so instead soldered a 1.8K resistor between 3.3K and PA12. I measured the connection with my Multimeter and sure enough I get 1.5K so the resistance is right but when I plug the board into my computer with the microusb windows brings up the error message "The last USB device you connected to this computer malfunctioned and Windows does not recognize it".
I have burned the correct bootloader onto it and can program using a USB to serial module and Arduino.
No USB though...hmmm... Can anyone help me with this?
Which particular bootloader did you burn onto the Bluepill?
i used "generic_boot20_pc13.bin" and I uploaded it using Flashloader demo. It all seems to work fine using the USB to Serial to flash Arduino code to it but the USB doesnt work.
Did you jumped BOOT0 to 0 before rebooting blue pill? If not bootloader gets erased! Don't ever move that BOOT0 after burning bootloader.
I've fallowed this video and mine worked:
Error you are getting on the windows doesn't mean nothing – if you pullup D+ or D- of the USB to 3.3v it will give this error, even if no device is attached to that USB.
Hi 3DGeo. Yeah I've done that. After re flashing, dont change jumpers while powered down... it still doesn't work properly. 
I've also tried running a soldering iron over the USB port just in case the port wasnt soldered on properly... still no avail.
Mubase:
After re flashing, dont change jumpers while powered down...
What?
You have to flash with BOOT0 jumper on "1" and after flashing WITHOUT POWERING OFF switch BOOT0 jumper to "0", and only then reboot and never touch BOOT0 again!
Follow the video I linked.
3Dgeo:
What?
You have to flash with BOOT0 jumper on "1" and after flashing WITHOUT POWERING OFF switch BOOT0 jumper to "0", and only then reboot and never touch BOOT0 again!
Yep..Thats what I meant. I :
- Moved Boot0 jumper to position 1.
- Flashed the bootloader using the Serial 2 USB .
3, Left the power on. - Moved the Boot0 jumper to 0.
- Pressed the reset button.
Green LED flashing slowly.
Correct no?
I think, didn't do that in a while.
Just get another pill and test with it, they don't cost a cow you know.
Btw, I hear that win10 do not like some MCUs USBs, you should try this with win7.