In the absence of the Chairman and Vice Chairman, the members present may designate an Acting Chairman, who shall have the powers and perform the duties of the Chairman during his absence. A majority of all members of the Board shall be necessary for a quorum, and all orders, determinations and other acts of the Board shall require the affirmative vote of not fewer than four members; provided, however, that the affirmative vote of at least 2/3 of the full authorized membership of the Board shall be required to grant a variance under N.J.S.A. 40:55D-70d. As required by law, the Board shall keep minutes of all its proceedings, showing the vote of the respective members upon each question presented, and, if a member is absent or fails to vote, the minutes shall indicate such fact; and the Board shall keep records of its examinations and other official actions, all of which shall be immediately filed in the office of the Board and be a public record.