Studer 928 group strip issue

[Shindoja]

Hi ! Im racking some Studer 928 strips for my home studio. I manage to make the preamp and line stereo strips fine but when it comes to the group strips ( for the compression ), even with no signal coming in, there is just a big noise coming out and the overload light is waving. Anybody could have a clue, help? I can provide more detail but just checking first ! Thanks a lot !