I have a QT-90, the unit was poorly packed and damaged by USPS. There is no way to return it, so I'm trying to fix it. The last unresolved issue is when I use record mode both decks work as expected, but when I press Stop the right head mechanism is not releasing and remains stuck in top position. I can't open a lid to remove a cassette. When I disassemble a boombox, remove right cassette mechanism and turning a flywheel with a wide belt, the heads are releasing. The head block is not releasing when I'm trying to push it by a finger. Something like a spring keeps it. When I try a record mode again, I'm getting same problem. Play, forward and rewind work perfect, but when I use Record - oops! The cassette mechanism looks too complicated for me, I'm not understand how it works. Is it mechanical or electronic problem? Will new belts help me? Thanks!