I’ve moved the game on a game a little in the last few days.
When I first tried the machine I tried to type in a four line program to output numbers so I could see if the machine was hanging or if the keyboard interface PIA was failing. At first I couldn’t type it in before the machine hung. I determined that this was overheating and found a cause.
Now I can type in the program but when I run it it crashes with changing errors. Sometimes it reports a bogus/ill formed error message. Sometimes it just hangs. If I press “Break” the machine restarts. I then type “OLD” and the program is still there. When I run it I get the same result.
I’m thinking dodgy a RAM chip. About half of the DRAM has been socketed.