Anti-theft radio code locked-up

[achoeypatkul@hqfaus01.unicef.org (Amnat Choeypatkul)]

     Hi guys,
     
     Help...help, pls.
     
     My '89-90 has an "anti-theft radio/cassette," brand name: 
     Weisbaden/Audi, (original installed from Audi) which the "anti-theft 
     code" has been locked-up ever since I bought it from the original 
     owner.  (The LCD display always shows "SAF e" when it's on.)  I check a 
     little booklet/manual--which came with the radio/cassette, and tried it 
     all step-by-step, however, it's still locked-up and doesn't work.
     
     Anyway, does anyone know how to reset this "anti-theft" code?
     
     TIA,
     Nat