I pulled the cube apart, inspected and tightened the heat sink screws (just a little).  I swapped board 4 for board 6 (only the first 3 boards were hashing).

It's back online at LOW clock.  The first 3 boards are hashing well and board 4 has a few chips that are hashing and they are doing poorly, board 5 and 6 are all zeros for hashing but no boards are showing up as dead Xs.

Total hashing rate is 12,599.

I have to admit that my two cubes have been nothing but problems since day one.  Nice concept and good form factor but problems on the inside.