Restoring and Demoing 1960s Vintage Computers at the Computer History Museum [pdf]

When I started at IBM back in the 80s in NZ, there were plenty of 1403 printers still in operation, though no 1401 CPUs.

Since they were old even then, and NZ was something of a computing backwater (on a training course I met a guy who's territory of 3 or 4 floors of the world trade center had more machines than my territory of half of the North Island) there were no formal training courses on them, and I was on my own with the manuals and the insights of the gray beards in the company lunch room.

It wasn't until I found Ken Shirrif's magnificent animated explainer https://ibm-1401.info/KenShirriff-1403Animation.html many decades later that I really understood how the machines I had been fixing worked.