I think I almost have the tape deck fixed on my M90, all I need now is a new belt. And I think the reason the FM doesn't work is because there was a bit of corrosion on the board that caused a "Trimmer" (might also be called a potentiometer) to corrode to the point where one of the posts that makes contact with the board broke off. Someone needs to go back in time and tell people that boomboxes are not meant to be used as coasters for their drinks.

The writting on the board next to this trimmer reads "V R 2", there appears some writting on the trimmer itself that reads something like "103a". Anyone know where I might find a replacement? Tried asking the guy at Radio Shack and he was of no use.
http://i27.tinypic.com/2rdf6ts.jpg

That is the FM oscillator pot for FM stereo, replace it and it will be golden again.

Members here have sourced that part......they'll chime in.