Must board members vote on an item if they are present and do not have a conflict of interest?
There is no requirement that board members must vote. There are no legal penalties for not voting. The Oregon legislature has recognized in statute `conflict of interest' as one reason for a board member to not vote. Oregon defines actual conflict of interest as "any action or any decision or recommendation by a person acting in a capacity as a public official, the effect of which would be to the private pecuniary benefit or detriment of the person or the person's relative or any business with which the person or a relative of the person is associated." ORS 244.020(1) When you have such a conflict you must declare it, explain it and abstain from voting. The vote is recorded as an abstention. If you have a potential conflict of interest, you declare the conflict but still vote.
I have seen board members abstain when they know that their vote would be considered biased should there be future legal action. For example: A complaint was brought by a parent against a teacher, and a board member got in the middle of the situation and publicly declared that the teacher was wrong and should be fired. After going through the district process, the teacher appealed the disciplinary action to the board. The board member should abstain because the teacher could later contend in court that the board was biased based on this board member's level of involvement.
Oregon requires a quorum of the board to vote in the affirmative to pass a motion. This means that even if only three of a five member board are in attendance, all three must vote yes to pass a motion. In most states, and by Roberts Rules of Order, passing a motion requires a majority of the board members present, two of the three, to pass a motion. In Oregon, all votes to abstain and all board members who are absent have the effect of `no' votes. Unfortunately, this is sometimes used by board members as a way to vote no without having to go on record as having done so. This can anger board peers and members of the public - when they figure it out.
In short, you can abstain for any reason and no one can make you vote. If voters believe you are shirking your duty by not voting, they can choose not to re-elect you or they can recall you. You are required to state the reason for your abstention when it involves a conflict of interest, and it is good practice to do so for any abstention.