In trying to help someone having a problem with their "Play Ball", I was looking at the schematic and wondering what could cause the O relay to burn up. Here's the relevant part of the schematic:

Play Ball O relay (resized).JPG

I see that the ball drains, closing the Ball Return switch, which energizes the Q relay, which energizes the P relay, which turns the score motor and energizes the O relay. If the O relay is working correctly, the P relay would then turn off at the end of the score motor cycle. The O relay has to stay energized to launch the ball when the right flipper starts the score motor:

Play Ball Ball Shooter circuit (resized).JPG

It looks like the O relay stays energized until 10 or 100 pts are scored (M or L relay fires) to open one of those 2 switches in series with the O relay. It also looks like this happens with every ball, unlike games that use a First Ball relay.

What keeps the O relay (or the Q relay, for that matter) from burning up if someone walks away from the game with a game unfinished and the ball sitting in the outhole? I guess that was unlikely to happen when the machines were originally routed, and people were paying for each game - so maybe it wasn't a consideration for the designer. But in a home setting, I could see the kids playing the game in the basement, getting to ball 3, being called up for dinner, and forgetting about the game for a couple of days, or until the smell brought Dad down. Or in a modern arcade with a flat entrance fee and all the games set to free-play, people are constantly starting a game, losing interest and walking away with a game unfinished (usually a 4-player game...oy!).

Am I missing something obvious?

Hey Howard - nice to hear from you. I'm glad my reasoning is sound. I don't know that the person is up for any major changes - I just wanted to be sure that he'll know to play complete games on the machine. Wouldn't be a good machine to have in a public arcade.