just picked up a Street Fighter 2 machine......

After a bit of work it seems to play normally, however, when I press the credit buttont to empty any remaining credits, the machine completely empties the hopper then gives a hopper empty error.....once stopped the same happens if I try a soft reset by turning the door key left ... also activates hopper and doesn't stop.

Any ideas what the problem might be ?

Cheers

BIG S