Researching the Sharp GF8989 I came across a Youtube video, thought you all might appreciate the third comment, credit to 'Open Roader' for being so polite and understanding in his response.
'Hi i just found a sharp GF on the side of the road, in pretty good quality too! the radio works, but i can't get cassettes to work on it and i think it's because of the 3 digit combination lock but i don't know how to reset it. anyway you seemed to know a lot about stereos and fixing stuff, could you help me out?
+Miranda Ralph The 3 digit number isn't a combination lock, but a tape counter. It lets you know what position the cassette is in. You can play the cassette to the beginning of your favorite song, push the button and it sets the counter to ZERO. then when you play the song and it's over, you press REWIND until the counter comes back to ZERO. Then you are at the beginning of the song again. Your deck isn't working because it probably needs new belts.