I am a Electronics Tech by trade, since you can turn the machine over and the problem goes away, that tells me there may be a cold solder joint. Now the issue is that there is surface mount technology most likely on that board. Plus it will be fine pitch meaning it is very small leads on the chips. I used to be able to touch up solder joints on surface mount chips but they have gotten finer and finer. But there is also thru hole technology on boards also that are bigger in size and easier to touch up the solder joints. There could be residue on the board that with moisture made the residue like bloom or corrode. This could cause erractic behavior. Cleaning the board with a circuit board cleaner like from radio shack might help also. Visual inspection of the board with a magnifier glass might show something , you would be surprised as its most likely something simple , most times it is. A good tech always looks for the obvious and most times it makes him look like a genius. Cold solder joints are not shiny but rough in appearance. Good Luck.
