This machine is from Vic's sell-a-thon a year ago, and has been playing fine until recently. Occasionally now, when three in a row is made with the first three balls, as the fourth ball leaves the shooter lane the tilt light comes on, and of course no credits score. Need a little guidance where to start looking. I have the schematic, but have spent almost no time inside a bingo.

Thanks for getting back.

Credits are subtracted on tilt.

If there's no winner on the first three balls, when three in a row is achieved , whether on the fourth, fifth, or extra ball, the tilt comes on as soon as the ball drops in the winning hole.

No tilt on a winless game.

The tilt bob and slam switches look ok.

Sometimes credits are awarded, but lost if a score is made say in another row. I haven't figured out if it's only tilting in certain color rows or involving certain numbers.

Ran a few more test games, and it tilts on all color lines. It doesn't seem to be awarding credits occasionally as it would do a couple of weeks ago. I've done all my testing with the numbers in home position, so will try a few more with numbers rotated.

Looked over everything you mentioned and nothing jumped out at me, but...while running some test games it finally dawned on me that if the coin door is open during a game, scoring and payout is normal. The only switch affected by the door position is a small single switch just above the lock. I clipped it closed to simulate the door closed position, and the tilt occurs when a score is made. Haven't tracked down the purpose of this switch, but it's looking like an "easy" fix.

Actually this switch is separate from the lamp switch, which is a button mounted in the cab. The one affecting the tilt is a leaf switch mounted on the door that makes (closes) when it contacts a plate next to the lamp switch button. I suspect it's an anti- cheat of some sort, except it's working in reverse.

Here are the pics. The smaller switch on the left is the one in question (to its right is the yellow button switch stack). The other pic shows the strike plate for the switch and the cab lamp button below it.
Another behavior I noticed is that the main Tilt relay doesn't trip during this tilt event. In other words, the motors keep running, but the tilt light comes on and the credits zero out. I see an anti- cheat relay on the schematic, but haven't located it in the machine yet.

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There are three selector locks, pre 4th ball, pre 5th and after 5th.
It'll be a couple of days before I can look into this , thanks for your guidance.