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Sunday 21 January 2018 at 00:55
It's to the left of the 2 PIA chips positioned on the right side of the cpu board. I screen capped an image of the cpu board and drew an arrow pointing to the 5101 RAM chip. You may want to replace it with an NVRAM chip so you can eliminate batteries entirely.
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Source: http://pinside.com/pinball/forum/topic/black-knight-what-ails-thee-diagnostic-switches-game-start-issues#post-4186566