I was not able to flash my Gotek... I only constantly got "unrecognized device" no matter what OS or serial driver.
Finally, I found another forum unrelated to Gotek (ST Microelectronics) that some were able to use the 3.3V (from the USB-TTL line to the Gotek) instead of the 5V line. I tried that, and it worked first time.
May be of some help to people unable to flash.
I thought you were supposed to use the 3.3 v line. I don't have one yet, just heard about them a couple of weeks ago. I see you can get them for about $35 on Ebay (China) or a pre programmed one from various places for $60 - $70.
