I feel your pain Tony! Having come into this hobby with nothing in the way of electronic knowledge (I still have most of what I started with! :) I have spent many an hour tracking down the silliest of things!

In fact recently spent hours trying to get the special lamps on a Gottlieb CEOTTK going - changed everything in sight as I worked though all the possible culprits. In the end I was back at the fuse that had initially tested good. So I changed it for the heck of it and they all worked! Bloody fuse tested OK but just didn't work in the system!