I had the same problem. took unit apart and used a white rubber eraser on the button contacts and also on the rubber back of the button. Cleaning the rubber back of the button seemed to be the most important part because prior cleaning of just circuit board did not seem to have any effect. Button works fine now to my surprise. I suggest cleaning the rubber back of all buttons to avoid repeating process of having to take unit apart twice
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I had the same problem. took unit apart and used a white rubber eraser on the button contacts and also on the rubber back of the button. Cleaning the rubber back of the button seemed to be the most important part because prior cleaning of just circuit board did not seem to have any effect. Button works fine now to my surprise. I suggest cleaning the rubber back of all buttons to avoid repeating process of having to take unit apart twice