I got my 5 other GOTEKs today.
I managed to flash my first one on Win8.1 x64.
Friend could not flash his so took it to me. I could not flash it either.
Tried my first one again. Did not work. Tried on Win7 x64 as well. Tried more then 500 times but never managed to reproduce my first firmware upgrade. No idea why.
Got a tip to run the program in compability mode (XP SP3) and as admin. Did not work.
Got another tip. Run it in XP x86. I only had my GOTEK now but at least I could connect to it.
However, I did not get to select "STM32_Connectivity-Line_128k". I only got a list:
None of which worked.
Today I got my 5 other ones. Tried the first one in XP x86. Could connect to it and remove the protection. After that, the program froze. Had to restart.
After that, I did not get the "STM32_Connectivity-Line_128k" option when I connected to it. Only the damn list. None of which worked.
Now, up until now, I never got any contact when I connected VCC and GND to the power of the GOTEK. Only when using an ATX PSU for the power did I get any connection.
I read another thread that sayd you should have GND from the USB SER TTL adapter connected as well. My GND was occupied by the ATX power supply so I connected it to GND on the floppy connector instead.
Success! I got the "STM32_Connectivity-Line_128k" option again and could program the first 2 without any issue.
Tried the same thing on Win8.1 x64 without success.
Conclusion for me:
Use XP x86
Connect TXD, RXD and GND from the USB adapter.
Take power from an ATX PSU.
Here is a picture to illustrate how I finally manged to connect 100% of the time.