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.

Thanks for pointers I found the A15 Flipper sensor board. Its on bottom of playfield back. With MM i did a quick check on both circuits in board to see if I could find a bad resistor, diode or transistor. All looked ok but I have been fooled before as many times board needs to be powered on prior to cause the component to show signs of failing. Prior to checking with power I plan to trace and check wires from A15 to I assume to the A1 CPU board switch matrix. Gottlieb schematics more difficult to read that Williams.

So I looked at A15 sensor board. I could not find anything wrong. I could see the 033 black orange orange wire on flipper switch and on right coil. I also could see a 033 wire attached to A15 sensor board. I could buzz to switch to coil but not to the sensor board. As a sanity check I did same with left flipper. I could not buzz wire to sensor board from switch either. Left flipper button does register with switch matrix. So I know it works. I am not understanding something. Looking for ideas.

I want to provide an update. Still have not found issue but I have learned there are 2 A15 boards under playfield. I found right one now and connections from flipper coils to board test out as expected. All circuits and comments on board seem to check out so now I am going to follow to A1 board. I might have a bad transistor.

Locating the right A15 board was key. Once I was able to test the coil to sensor board successfully I then move on to testing the wire 622 (blue red red) wire. First switch I looked I found it. Broken wire broke circuit. Success. Thank you all for advise. You were right on, look at the schematic and trace the circuit.

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