I have a Cassette model Ultra radio and somehow found a loose hot wire that hit the bottom of the radio and fried the booger. I went to
www.radiosound.com/customer_service.php and called them. I paid shipping there and they had me another unit plus the cassette that was in my old back in about a week after I placed mine in the big brown truck.
It works perfect now and it only cost me $135 plus shipping up there. I am not sure about cracking one open to replace guts. It seems not cost effective and a 90 min cassette holds more music than a 80 min CD. Plus it is cheaper to make.