Reaction mechanism for the synthesis of 9,10-phenanthrenequinone
Here's what I was thinking.


  This probably happens via a single electron oxidation of that double bond to a radical cation as a first step. The cation can trap water and then we can oxidize the radical to a cation. Eventually, you get to a diol which you can oxidize to a diketone.




I ommited the steps for chromium oxidation from the alcohol to the ketone. Sounds like you are already familiar with those.