Looking for some basic troubleshooting practices on what to look for when verifying things like switches or optos are working when you are not getting an error code.

I have an earthshaker machine that will constantly search for balls on power up. This issue was intermittent and used to only go through one or two iterations, but now is permanent. I believe it's the switch that the balls sit on before being kicked over into the shooter lane. I don't see any other optos or switches in the trough that could be the culprit. The coil that kicks them over worked fine as soon as the balls were found.

Before I start buying parts on marco is there a way to test the switches to ensure they are working? I don't get any error codes and pressing the start button just starts another ball searching loop.