Mycenter 1 random freezing and unfreezing

I was asked to try and find the issue of a Mycenter 1 (1984) that randomly freezes and unfreezes without any interaction to it. The very first symptom described is that the initial boot up is sometimes very very slow (it can take 5-10 minutes to boot at times), but other times it will boot almost instantly. Once in operation everything can stop at any moment. Without running any jobs and only moving the axes eventually everything stops responding. And again, without doing anything, trying the controls after a while and the axes move again, until they suddenly stop.

I have no experience at all repairing milling machines, but I am an electronics tech for 20+ years. The motherboard looks in good shape, although it has very old capacitors and a bunch of ICs on sockets. I am looking for any help at all with this machine. Any manuals, block diagrams or charts / test points list and their value available so I can start looking up stuff? I have no reasons to think that the issue would be elsewhere than on the main motherboard.

Also, besides a retrofit, any possible ways to increase memory?

Any insight is greatly appreciated! Once the capacitors are changed I will reinstall the board and then try disconnecting sections and see if they influence the machine freezing or not.

Thanks in advance.