You are correct, the start button does make the changes but isn't needed to do game testing. You also don't really know if the start switch is working until you place the game in switch test and then push it. So far everything that you have described could be some other issue but you won't know for sure until you run the test. Check all the switches for activation, but also make sure to hold each switch long enough to register 4 times and that only the one switch shows on the display. If 2 or more switches show up on the display you have other issues. You also need to remove the balls while testing for other switches. With balls removed and no switches pressed nothing should show on the display, it if does you have a switch that is stuck closed. This will need to be fixed first to continue the test.

That is not a slam switch. The slam switch is on the back of the coin door, it keeps people from kicking the coin door.

Playball!