I believe that if the first vote does not get the required amount of delegates, then all of the delegates are free to support any candidate. They are released from their pledges. It is not after multiple votes.
I think in general you are right ... although some states I believe specify that delegates are released after 'x' number of ballots. And from some states they are not bound even on the first ballot.
But my point was, most of Romney's delegates, for instance, are going to vote for him, not because they are bound to, but because they want to ... else they would not be Romney delegates.
So if Romney or someone else doesn't have the majority on the first ballot ... most of his delegates are not going to say, "Well, so much for that ... let's pick Thompson." There will be efforts to persuade and make deals and swing enough delegates so that their guy wins.
So by far the most likely result of a brokered convention is that one of the guys that goes there with the most delegates ends up winning. And only in a case of deadlock after several ballots would there possibly be a move to consider a compromise or consensus nominee.
And that consensus nominee is not likely to be someone that we hard-headed conservatives would like.
This is all conjecture, of course ... it hasn't happened in so long it's hard to know how it would play out ... so I don't mean to try to sound like an expert. Just saying, a brokered convention does not equal a reset where we ignore who has delegates and pick someone from out of the blue.