Quoted from fredsmythson:

The 6 volt switches of the coin unit are in the correct position. So, there might be an issue with the 25 volt switches on the coin unit. Examine the coin unit and it's switches. Check to see if the switches are dirty or out of adjustment. Make sure the hub screws are tight on the coin unit... Also, look at the score motor and manually turn it to see if all the switches are opening and closing properly. Sometimes the switch stack fingers that ride on the score motor discs can be out of adjustment and it will cause issues with the coin unit...

Quoted from fredsmythson:

I was reading off some Spirit of 76 information, so it looks like the two player and four player machines control the player up feature differently. ajfclark , do you have a section of the Pioneer schematic that shows the coin count relay circuit?