Hi all. I really could use the help of those of you who are switch matrix experts (and even those who aren't but still get by). Sorry in advance for the long post, but this one has me baffled. It presents as a shorted diode, but all diodes have recently been replaced, and the ones I've tested so far appear good.
The issue is this, when two switches are closed in the matrix, and you touch a third switch, a fourth switch will register. This is always in a rectangle on the matrix. This is why I had thought it could be a shorted diode. I watched terryb excellent YouTube video. I am posting a clean copy of the switch matrix, and a copy that I marked up with rectangles. Each rectangle represents an instance of where I have closed two switches, closed a third, and had a fourth register. For example, if Drop Target "C" and Drop Target "D" are closed, and I push on the right slingshot, the left slingshot (and not the right) will fire.
All rectangles have Drop Target "C" in common as one of the corners. I checked and replaced the diode to that drop target, but the issue continues.
I am in the process of tracing the wire off of the drop target to ensure it is intact and not shorting somewhere. So far, it looks good, but I haven't finished tracing it yet.
I checked the MPU by removing J2 and jumping the columns and rows, and all switches register as they should in switch test mode.
I have checked all of the diodes in some of the rectangles, but I have not checked all diodes in all rectangles yet. Though, the previous owner reports that he replaced them all when trying to diagnose this issue himself.
Is there something obvious I'm missing? All help is very much appreciated. I would very much like to get this great game running 100% Thanks!
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