Melted ground wire?

[kostaktinos_mt]

a [minor] possible scenario is that the external bec losed contact on it`s own ground wire. that would mean that the current flowing through the bec circuit circled through the mm bec`s ground and the ubec`s positive. what caused that much current, is unknown to me; maybe a stalled servo...
in this scenario however, the ubec`s red output lead should be stressed as well [unless it`s thicker wire]...

just an idea...