I just picked up a Stargate. After first glance I thought all was working but after 1 game I realized that the right flipper select function did not work. Flipper work fine, balls are hit but select does not work. For example during game play it asks you a question left flipper no or right flipper yes. The left flipper seems to register but not the right. So I went into diagnostics mode. I can scroll through menus with left flipper button but I cannot select with right flipper. Gottlieb very different than Williams games. There is no transit or for flipper. Thus no CPU switch register I can see in manual. Flipper button makes switch contact and power flows to through coil. Which brings me to my question. How does the CPU know the switch is triggered? Any assistance understand how this works would be appreicate. Even better I am looking for ideas what I should check to fix.