Adsense Quality Rating

Got one of my sites banned, first Adsense not showing, then deindexed. It was responsible for only about 10% of my total Adsense revenue. No other sites got any penalty.
From that day on, my Adsense revenue dropped 70%. NOT 10%, as expected, but around 70%!
Reason? My “Adsense Quality Rating” plummet. Its the second time this happens and the first time it took me more than a year to get a good quality rating back. But I could easily noticed when my good rating was back: revenue suddenly jumped 200% without any change in traffic.
Thank God, Adsense is currently only a small slice of my income pie.