Go under the playfield and carefully inspected the spinner switch.With the playfield cropped up with the metal rod locked in place you will now be able to can take your finger and manually spin the spinner watching carefully to see if the switch is too close,twisted or bent out of shape,etc...
These switches can be tricky to set up especially after someone else might have tried to tweak it. I just set up two spinners on my Williams Blue Chip and spent some serious time dialing them into perfection.I was lucky though because the Blue Chip has two spinners which gave me a reference point since one of my spinners was working very good, but not perfect.
Take some pictures of your spinner switch under the playfield and post of possible....maybe we can see something not right and explain to you how to correct it.Make sure you use a bright light and magnifier too if it might be helpful for you.
BlueChipRestoSept14 062-401.jpg