It may be a little painful to watch John who doesn't really have any idea what's going on, but he's managed to make quite a fair amount of progress through trial and error and lots of outside help (both good and bad advice) - but mostly it's completely fascinating to me to see physically this historic device, a solid state machine using only TTL chips with no CPU/RAM/ROM - plus the tools used to diagnose and address issues on the chip level. Also -- hooray for industry standards allowing replacement of a chip from another random board produced a decade later.