Yosef Karo

“ Nor can he judge one whom he hates, even though he is not a actual enemy whose downfall he seeks. Rather the two litigants should be equal in the eyes and hearts of the judges. When he does not recognize them personally or know of their behavior there is no more righteous judge than he. ”

“ One litigant who claims that the judge loves or hates his counter-litigant is not believed, and he needs to show proof of his charge (Tur) . One who is excommunicated because he shamed his friend is able to judge after the ban expires, as he does not really hate him. ”

“ A convert can judge another convert even though his mother is not Jewish (See Yoreh Deah, chapter 269) .
7:2 A mamzer, or even if all the judges are mamzerim - they are permitted to judge any case. If all of the judges are blind in one eye they are also permitted to judge (ur5) . Howver, one blind in both eyes is disqualified. ”