Random crashing you say? Sounds like poor contact on the socket over the 68000. All pins clean? Loose fit? Weak pin springyness? I've read of microfractures too on the 68000 soldering. Different A600 motherboards (not necessarily same revision) will have a different height of the surface mount chips and slightly different 68000 pin angle/mass. It could be that both of your boards are lower slightly or otherwise presenting less pin to the Apollio socket, making a less secure and less electrically sound connection.
