90% of the time when a voltage booster type BEC craps out (it did it to me as well, years ago) its one of the capacitors in the circuit. The BEC in this mode is actually a regulated dc-to-dc boost converter, and is actually quite simple in its design, but in normal operation it can cause voltage spikes that are hard on the capacitor over it may fail for any number of reasons. Determining exactly where the bad component is on the board and then replacing it may be difficult. If you have a good multimeter, check every capacitor on the board and see if one of them has an internal short or something. I would bet more than even money that's the problem.

Another useful piece of info is that if you can't replace the bad capacitor with an identical unit that's fine. You only need a similar capacity, not identical.