Help! Sid v3 - Core v3 interconnection problem. CS#=0V, D7=5V

[extremist]

Hi all, the beautiful community

My midibox sid has just got born. I noticed some problems with the sound. On sidplayer mode some certain sounds are inconsistent. They are sounding low or none and some second you can hear them then again they sound low.

I made a deep interconnection test and the result is: on step CS#, all digital pins are 0 as normal but D7=5V

I am suspecting from one or both of the 74hc595. 

Any ideas?

Thanks