I am not clear on what you mean by Master Status switching is not working, can you elaborate? If it was working before and then stopped, I would first start looking to see if all of the cabling is seated and there are no bent pins. You could also try re-seating the Logic cards in the 651. Typically when recapping a console, just the electrolytic caps in the audio path are replaced. Shouldn't have much of anything to do with the logic at all but who knows, it depends on the tech.
S10 I believe just routes the Group signal to the SubGroup input of the SL611, dealing only with internal routing. When you are using the routing matrix and not getting a signal to a group, can you route it to the mix bus and hear it? It seems that the only thing that would not allow a group output to pass a signal would be a daughter card issue on the SL611, and assuming that every channel in the desk is experiencing the same problem is highly unlikely. I would trouble shoot this channel by channel before digging into it to deep and looking elsewhere.
Hum on your monitors could be several thing. Proper grounding would be the first thing to check out. VU Meters or Plasma? Ripple or AC voltage on your DC Supply rails could be another cause. A good practice to follow (especially if you are running all on 120VAC) is to have the console power supplies and your monitoring on the same leg in your breaker box. I have seen some strange noise issues when installing consoles in houses or facilities with no tech. power.
Hope this helps,
V
