The problem could also be the coin lock out coil behind the unit in question.
Check to see if it pulls back and the armature spring is intact.
Or
There is a possibility that it has debris inside. Try using compressed air on it.
Open the magnet door, check the magnet for any partials stuck on it.
Inspect the chute prior to the coin mechanism.
[size=78%]Check for anything that might interfere with the coin.[/size]
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Place the unit on your work surface, propped up high enough for a coin to come out.
Adjust the magnet by turning the screw out until it stops the coin.
Then adjust the screw in until the coin drops through, hopefully into the correct chute.
Note, this needs to be done on a level surface. If the procedure is done in the door, the angle of the door will effect the adjustment because the coin will travel faster when the unit is leaning to the right.