Hi Martin,
a few days ago I tried guiding with my QHY678M. However, I could not connect to the cam with PHD2. On connection the cam shows up in the device manager but PHD2 says no camera connected. I downloaded and installed the latest beta version of the QHY SDK without success.
I also tried with my QHY174M and that gave me no problems.
Have you been able to figure out a solution to your problem? What are your connection settings in PHD2?
Best regards
Christof