Check if the harness from the power supply to the MCU is delivering power. That's what happened to our Solar Ride, the symptoms were identical, would boot, but wouldn't coin up or start and no clicks - when I bent back the connector pins to make contact, the game started working again. I've since repinned the connector.

Use a multimeter in DC meter mode on the upper power supply connector. On the power supply board, there should be five wires, left to right, coming from the connector. They are in this order: 5V, 5V, Ground, Ground, -12V. Start there to see if it's outputting those voltages.

If the 5V is low, there will be two "pots" on the power supply. The leftmost one will adjust the 5V.

Do note that the connectors in that harness may have gone bad - this is what happened to ours. I was able to bend the connectors back and get it to work, but I repinned them at the first opportunity rather than risk another failure.

That sounds like it's within tolerances. The main board... it's always possible it's only getting part of the 5V, even though you're reading it there, since there's technically two lines to ensure enough amperage gets to the MPU.

Does the system coin up, or can you get it into the menu via the test switch at the top of the coin door?

OK, so that means the MPU is getting all the power it wants, and eliminates that harness as a possible culprit. Our problem, we couldn't even to get it to hit the test menu.

I'd check to see if the coin switches are indeed making contact, as well as the recommended cleaning of those lower left connectors on the MPU, as well as the connector pins in the harness that attaches there. You can also check, in the power supply panel at the bottom of the cab, on the left of the bridges and above the fuses, there will be a small breakout panel with about five diodes on it tied into the harness going to the coin door. One or two of those should be to the coin switches, and should probably be checked as well. The rearmost one will be to the test switch, and can be ignored since that works (it was actually broken on ours when we got it, which is how I know that's the one to that switch).

I don't know if it saves the credits - the battery on ours was removed a long time ago, and I won't be fitting a battery until it's working and after the housewarming in a few weeks, so I can't even test it. I do know some people can basically make it so you add a credit and start a game by pressing the start button. Ours actually has a dedicated "add coin" button added to the cabinet, so again I can't verify that.

Odds are pretty good that if it's constantly adding credits, you'd be hearing the credit chime again and again... unless they turned the chime off via the DIP switches, and even then I'd think you could literally watch the leftmost two numbers on the four digit credit/ball display constantly climb and have trouble starting a game.

Check the pop bumper from underneath and see if you can move it freely by hand. It should move easily. If it has any resistance, replace the coil and sleeve.

On the rollovers, I've noticed that on our machine, they also don't register every hit. More often it won't register when the ball goes up rather than down.