Pinball theory

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Theory is when you know everything, but nothing works. Practice is when it works, but you don’t know why.

I know all the theory of how the start button on my pinball machine works.

  • I know that the switches are arranged in an 8x8 grid of rows and columns.

  • I know that the micro-controller runs a bit across the columns and reads the row inputs to identify closed switches.

  • I know that the start switch is on row 3 of column 1

  • I know that the row wires are all white with a coloured stripe and the column wires are all green with a coloured stripe.

  • I know that the start switch is connected between a Green/Brown wire and a White/Orange wire.

  • I know that these wires are connected through the Coin Door Interface Board, entering on pins 2 and 7 of connector J6 and leaving on pins 1 and 4 of connector J1.

  • I know that connector J1 on the Coin Door Interface Board is connected to connector J212 on the CPU board and that the Green/Brown cable goes to pin 1 on this connector and the White/Orange cables goes to pin 7.

  • I know that the start switch signal goes through diode d4 on the Coin Door Interface Board.

  • I know that the start switch has a resistance of around 10 ohms when closed that I can measure this at the connection to the CPU board.

  • I know that other switches on the same rows and columns as the start switch work perfectly fine.

And yet it doesn’t work. I don’t think it’s called “The Twilight Zone” for nothing.