until then, use only a 6V adapter for externally-powered Freeduino SBs!
Hmm. I notice that my freeduino SB has a 7805 regulator, which means it won't produce 5V out of the regulator with a 6V input. :-(
On the other hand, I also noticed that the holes provided for a higher power regulator ALSO provide a means of "fixing" the board for higher input voltages without too much trouble.
1) remove the low voltage cap from the position near the connector. Try to do this without damaging the traces of the PCB (unlike my attempt.) Note that it's OK to destroy the cap, cause it won't be useful.
2) install a new through-hole cap in the bottom two holes provided for the regulator, with the minus side up. (GND is the center pin of the three for the regulator.) Anything from 47uF (standard arduino value) up, at whatever voltage you intended, should work fine. The photo shows a 220uF 16V cap I happened to have.)