thanks. You are right. It´s not a Simvim and not a soldering or cable issue.
I have found the reason. The PF3 ATC tool from Oncourse is the cause.
I have double checked. During flickering i have shut down PF3 and the flickering is gone in this moment.
So maybe, PF3 adjust anything about the HSI Course.
I will look further into this issue, maybe i will find an option to prevent PF3 from adjusting the HSI Course.
If so, i will report here. Maybe this is interessting for other PF3 and SimVim users.