I can't get too technical here Mike but I had a 9512 that had some sort of problem. My technician friend came around but couldn't help. Despite me pointing out that it warned you in the manual NOT to switch on without the printer plugged in-he did
As a result it appeared to be completely b******d. Apparently the main [only] chip was destroyed if you did this [somehow].
I discovered later that the only possible repair was another chip. I found a supplier but didn't pursue that in the end. I'm pretty sure it was the Markl 1 version though.
My technical knowledge is very limited and I doubt if this story will help you much but it might have been worth repeating. Of course the notion of a computer with no memory except on the individual floppy discs would be hard to get across to most people these days-like a phone that just makes calls
Dave W