This is a rather excellent piece of work by a fellow in Finland (I think). I have not seen it posted here and I emailed to ask if I could post his files but have not heard back from him. I don't think there is anything wrong with posting the URL of his web pages.

https://ketturi.kapsi.fi/2017/10/reverse-engineering-emco-cnc-video-controller/

Again, excellent work. I used it to repair my video board which was missing the character 'dot' in the 3rd column.