With a 50% mixture of vinegar and water clean the board thoroughly, then rinse with water and then alcohol to remove the water. You can dry it with a hair dryer. Don't get any water on the dip switches, I doubt they are water tight.
Exactly 100% right there Nick. I'm actually refurbishing six Bally -35 MPU boards with mild to bad corrosion. One of them is particularly nasty !
I've covered this process here -
http://aussiepinball.com/index.php?topic=2343.0I have a board I used for testing that was a total wreck. The vinegar trick works very well, as I refurbished this board 10 years ago. Not a trace of corrosion has re appeared.