I have a pair of M7 II's circa 1991. The tweeter on one of them is not working at all. There is no fuse on the back of the unit. The midrange and woofer seem OK. Thinking the tweeter was blown, I ordered a new one from polk. The original tweeter is an SL 2500. I read Average Guy's post from 3-7. He had a similar problem with an older M7 but a new fuse fixed the problem. Can anyone offer some help? Thanks.