We left off with our CPU board stripped of no-longer-needed chips. It dawns on me that I didn’t play “one last game” before dismantling things. Too late for that I guess. Oh well, on to the task at hand. We need to make a few decisions, add a few connectors and rig up some cables and see if our “theory of operation” holds any water.
Back from vacation! I’ll try to get caught up.
In our schematic exercise, we took a good look at how the CPU board routed the data bus using two chips for address decoding. Given this good look at how the hardware is wired together, we should be able to throw a bunch of stuff out and wire in a new controller. Time to dive in and start taking things apart.
Where were we? Oh yes.
The CPU and SOUND board Theory of Operation writeup tells us that U213 and U214 comprise the address decoder for the cpu board. We’ve been able to trace the data bus to a variety of sections (or systems) on the CPU board, discovered signal leads that are used to enable the systems, and traced those signals back to the address decoder.
We can now take a slightly more detailed look at the decoder section and muse about what the CPU must be doing to drive the game. Read on…
To understand what we are trying to accomplish, everyone will need to learn a bit about how the electronics in the pinball machine work. So I now present to you my low budget tour around the electronics.