Usually when people have issues with their automatic belts I tell them to go to a dealer because the US government requires all carmakers to provide lifetime warranties on seat belts and their related parts.

If that option isn't available then you'll have to get your mechanic to troubleshoot the automatic seatbelt system. It could be a busted motor, something wrong with the control unit (the "mini motherboard"), or simply a bad wiring connection. If your guy has the shop manual for the car there is a troubleshooting section which starts on page 23-245, assuming he has a 1993 manaual like mine.