I had something similar happen. I was at the old Hughes terminal in Vegas waiting on my plane. There was a bank of nickel machines on one wall and I played a few with, of course, not good results. There was one machine in the middle that was buzzing and whirring all by itself so I had avoided it. I finally decided to put in a nickel and see if it worked. Not only did it work but that one nickel gave me two credits. It was a three coin machine but being good at math I figured out that getting two credits for one coin was better than three credits for two coins (the payout did not give an added bonus for three). After 90 minutes I cashed out for $13.50 and my right arm was sore for two days from pulling on that one armed bandit. Not a huge win but a lot of fun.