I see that you bought the game in May, when it was summer. These sorts of things can happen to EMs in northern climates when winter rolls around. The humidity plummets, which makes the switch stacks contract. This can affect the reliability of their make/break action. This is why it is important to make sure all switch stacks are screwed down tightly before making any adjustments. If they are not tight enough, the adjustments will go out of alignment when the climate shifts.

When the ball drains and no bonus happens, it sounds like your “Bonus Score Control Relay” might not be energizing. It is closely tied in with the circuit for the O relay, which is what sends the ball into the shooter lane. It sounds like this is happening when you successfully start a new game, so that rules out some of the contacts in their shared circuit as culprits in this problem.

If I had to venture a guess, the make/break switch on the DX relay and the make/break switch on the 15th position for the bonus unit might be the problem. You can see these two switches annotated in red below. The yellow line is the complete circuit for how the G relay initially gets energized.

G Relay Circuit (resized).png

In a prior post, someone recommended to me a "lightbulb tester" to debug stuff on EM's... not a tester for lightbulbs, but a tester made of lightbulbs. Rig up something that can handle about 30v, and it's a great tool for tracking down problems, especially intermittent ones.

I took an old string of dollar store Christmas mini lights where the bulbs are in series, and cut off the first three sockets (so I'd have a nice long cord to connect them in the pin). Shrink tubed the three bulb sockets together, and replaced the bulbs in the sockets with three 12V bulbs (that was the largest I could find off the shelf) so that they could handle about 25V-30V. Cut off the plug and put on alligator clips. Clip one end to a ground (one is right beside the game counter at the front), and clip the other to the signal your tracing.

Great tool for tracking down the kind of stuff you're looking it, as it responds quicker to pulses than a DVM does. Added bonus I found out when I started using it; not only does it show you if a signal is getting through or not; if it's getting through but is a shitty signal, then the lightbulbs are dimmer, so switch needs to be cleaned. Strong bright light pulse on one side of a switch... weak dim light pulse on the other side of the switch.

Recently debugged a problem where coin stepper relay seemed to be firing, but wasn't advancing the stepper, lightbulbs showed a weak dim pulse, but on the other side of the motor switch driving it, it was bright and strong. Cleaned that switch and problem resolved. Also had an intermittent problem with the bonus stepper very occasionally not advancing correctly, then rectumfying itself; but it has a lot of switches in it's path. I connected the lightbulb tester to one signal, and put the lightbulbs on top of the playfield on the right side over the shooter lane, and put it all back together.... when the intermittent problem came up again, I could see on the lightbulbs if something wonky was going on with the signal I was monitoring... I'd just keep moving it along the path until I finally found the one that was flakey.

I'm currently trying to debug a problem where on one score wheel, I'm occasionally getting the 10,000's number rolling over two numbers instead of one. When I connected my lightbulb tester to the relay, I can see that whenever it jumps two numbers instead of one, I'm getting some kind of quick double flicker on the lightbulb... the switch from 1000's 9th position is either flakey, or something else is occasionally giving me two quick pulses instead of one on my 10,000 relay. I'd never find something that subtle with a DVM.

Best and cheapest tool I have in my EM arsenal now!

76EF1485-DA83-4B0D-A1E3-FD2D43A6A074 (resized).jpeg