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Sunday 26 November 2017 at 13:04
The confusing part to me is why didn't the factory reset change the coin settings back to default? @ltg answer should have fixed it. It shouldn't be possible to do a factory reset without the coin settings going back to factory default.
Source: http://pinside.com/pinball/forum/topic/williams-sys-9-will-not-add-credits-or-start-game#post-4092468