Checking a tweeter is simple enough if the op has a multimeter. As Ben stated checking the crossovers would be a good idea under the circumstances. With minimal effort we should be able to help monkeyplasm figure out the issue and from there the cause. From what I have read of the 2150 I see the speakers going before the receiver but failures do happen.

I would hope the op has never turned the 2150 to max volume but from some of the posts it sounds like op feels it would be alright to do so.