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Alkaline batteries can leak aqueous potassium hydroxide, which is a basic solution. The best way to clean battery corrosion in this instance is with an acidic liquid. Pour a half teaspoon of either white vinegar or lemon juice into a bowl.

So, this required some hard cleaning first with vinegar followed by isopropyl alcohol.

I was getting a constant voltage on (3) when I should have gotten 0 volts. Seems that the battery acid/gunk must have been slightly conductive. A hard scrub to get ride of all the gunk seemed to do the trick.

Push Button

PCB Momentary Tactile Tact Push Button Switch

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Should be set to:

References