Playfield Up. Upon pressing start button, check and see how many steps the ball count unit stepper steps. Should be five.
See if you can manually step it up to five. Does it work freely or is it gummed up? You may have to clean the ball count step unit.

Check switch D on the Game relay. Does it need to be cleaned or adjusted?
Switch A on the coin relay appears to be working properly since it works on three ball play.

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