Hi
This might be caused by a leaking battery in the past. These Seiko movements with their white plastic housing parts are particularly vulnerable to that and very vulnerable in particular; these plastics tend to crack at the points where the screws are attached.
Have a close look at this first after disassembling the movement (a microscope is helpful)
If its all reasonably OK and you don't have to clean it from battery acid, clean the parts if necessary (carefully). Clean the circuit and the rubber connectors to the LCD panel (cotton swab and alcohol) and you might have a fully working A639 movement again
Be careful not to tighten the screws to hard as the plastics are very vulnerable to that, obviously
Goodluck!