Finaly, i repaired this chessboard last week. The most significant change was the replacement of the cpu by a brand new one bought on the bay.

Moreover, I've made a mistake by changing the capacity around the oscillator. I choosed too high value. My Eeproms seems ok now. I've already win and lost against the machine.

I wrote a short story about my quest on my blog. Sorry, it's in french. But you can download the schematics there. I have done it for those who want to preserve this "heritage".

Many thanks.