Can you post pictures of the circuit boards ?

I myself haven't worked on any Gottleib titles but a couple places I would start looking into it .....

http://homepinballrepair.com/index.php/gottlieb-system-80-cpu-repair/ ... the link for pinwiki worked for me from this site

( not sure if it'll work from here or not ) https://www.pinwiki.com/wiki/index.php?title=Gottlieb_System_80

I am suspecting battery corrosion and flakey connections

also add something to the title of this thread to perhaps draw others with "System 80A" games https://pinside.com/pinball/machine?query=&machine_generation=19#results