As Quench said you got some work ahead of you. Especially now you know the MPU won’t boot up. First thing is to remove ALL the corrosion – both sides. Any corrosion left behind will continue to grow. There’s several methods for removing it from baking soda to toilet cleaner. Remove the IC’s and give it a good cleaning. Look under the green solder mask. Scrape or sand away any loose solder mask and inspect the traces for any corrosion. The back side looks like it may have been affected too. You may have to do some trace repair. Corrosion can grow under the traces where you can’t see it. Also closely inspect any components. Replace any that look suspect. (They’re cheap and easy to replace at this point). While the IC’s are out, look closely at the sockets. Most likely the U8 socket is bad.
U8 and U13 are 5101 RAM chips. And they should be replaced in pairs. I’ve been having problems finding new 5101’s. If it were me, I’d replace them with NVRAM’s. This will also eliminate the need for a battery.
Quench also noticed the corrosion on the headers. To me, that’s the number one cause of failure. As standard procedure I always replace all the headers and crimp connectors on all the boards. Eliminating the corrosion, new headers and connectors and you’re on the way to a game that will last another 30 years.
Be careful and take your time removing components – especially IC sockets and headers. It’s very easy to remove the solder pad. Then you’ll have more work repairing your repair work.
Robotworkshop suggested you put covers on the EPROM chips. That’s a good suggestion. Ultraviolet light can erase the data on the chips. I usually put labels on all the chips so I remember where they go.Pb1010024 (resized).JPG