Quoted from mrm_4:
Im some what new to understanding how the matrix works myself, above I suggested the column of strobe 0 because it holds the tilt and the outhole which would lead to turns ending or games resetting. If drop target 4 has an issue what would that do in the way of what was described if the spinner is triggering the problem?
A shorted diode in the switch matrix will cause problems when the switch with the shorted diode is closed, along with two other switches: one in the same row and one in the same column. When you draw a rectangle through the three switches in the matrix diagram, the fourth corner will be the phantom switch closure.
Since Xenon is a multiball game, it's possible the three switch closures could happen with both balls bouncing around, but that would be unlikely. Instead, we need to look at switches that can be held closed. They would be the following:
Of course, stuck (misadjusted) switches could play into it too, so switch test should be run to verify no stuck switches (a shorted diode will not show up as a stuck switch.) We'll assume for the sake of discussion there are no stuck switches.
Looking at the switch matrix diagram, the side saucer doesn't have any of the above switches in the same row or column, so we can rule it out. The trough switch shares the same column as the spinner, but none of the above switches are in the same row. This leaves the drop targets, which are all in the same column. Note DT#4 is also in the same row as the spinner.
Drawing a rectangle using the spinner and DT#4 as two corners and another DT as the third corner you get the following:
DT#3 and credit button
DT#2 and tilt
DT#1 and outhole
Credit button and outhole switch closures match the symptoms described.
Here is what happens when DT#4 has a shorted diode and the spinner is hit:
Strobe 0 is pulsed, the signal passes through the spinner diode and closed switch and is present on return line I4.
With DT#4 down, the signal now passes through the switch and shorted diode, and is now present on Strobe 2.
If any of the other drop targets are down, the signal will pass through the diode and closed switch, appearing on the appropriate I line.
Since the MPU knows it sent the signal down Strobe 0, it will register all switch closures matching Strobe 0 and the corresponding I line.
So if DT#3 and DT#4 are both down and the spinner is hit, the shorted diode will allow the signal to flow the wrong direction through the matrix and appear on I5, causing a new game to be started.