How exactly is it set to "Free play"?

Some times, people cut the power to the credit wheel so that it cannot reduce credits.

Is the credit wheel on "zero"?

If you manually increment the credit to a value greater than zero, do you still have the same issue?

Marcus

After re-reading your problem, I noticed that your issue started once you attempted to manually simulate a coin drop. Did you use your finger or did you use a coin?

You should check your coin door for shorts or issues with a normally open switch that is closed.

I know that I had an issue where there was a piece of solder that was shorting a switch stack. Once the solder was cleaned up, the game started playing like normal.

Marcus