There are two common problems on the Marantz CD 94: the CD tray can often stop opening and closing, and the on /off switch breaking. The CD tray failing is normally down to worn drive belts or occasionally the commutator of the drive motor becoming clogged with grease.In this case, the motor checked out fine so the belts were replaced and all grease or scarf cleaned off the pulleys and other moving parts. Special plastic grease was then applied sparingly to the moving parts. However, the new belts did not cure the problem despite all parts moving freely as the small pulley wheel on the tray closure mechanism was still slipping. The solution was to add an extra drive belt to operate the tray closure solenoid. perhaps the pulley had become poised over the years, but two drive belts is now giving perfect, reliable operation.
The on /off switch fails because the plastic operating arm is very flimsy, despite the battleship build of everything else. So I re-fashioned a new end of the operating arm from epoxy and the on /off switch is now working reliably again.