The printer that wouldn't print: Fixing an IBM 1401 mainframe from the 1960s

It's rare to see a transistor opened up today to see what went wrong. From the 1950s to the 1980s, the USAF did that on occasion. The USAF had a project, the Air Force Reliability Program, to make electronics more reliable. About 1% of the electronics boxes in the USAF were stickered with a note like "USAF Reliability Program - do not repair in the field, replace and ship back to ..." Back at Reliability Program HQ, technicians would figure out exactly what had broken and document it. All the way down to the individual component level and below. Transistors would be opened up and photographed under a microscope to see exactly what went wrong. They found problems like this bad transistor in the 1401, where a lead wasn't attached properly.

The USAF followed up by naming and shaming manufacturers. Microphotographs of bad parts were published in Aviation Week. Parts got better.

Even not understanding most of it, I always manage to learn several interesting tidbits.

On some printers you could change chains for particular print jobs - when we printed some jobs we'd load up a chain with just digits on it (so the printer could print an entire line while the chain moved 10 locations rather than 48 locations - theoretically 5 times faster.

Page layout was done with a loop of paper tape N positions long (that matched the number of lines on a page) and 10 widem each one of 10 horizontal holes corresponded to one of the fortran carriage control commands "1" meant "skip until there's a hole in position 1 on the tape" - you'd change to a special loop when printing labels for example, or for different sized paper - if you made a loop and were stupid enough not to have a hole in each horizontal position at least once around a loop skipping to that position would result in a "page throw" fanfold paper would exit the printer horizontally until it hit the wall and would continue to do so until you ran out or someone noticed

She was gone 3 days before we could no longer print. I remember talking to her and her complaining that we were using too much space for emails, and whoever set up the Network put the email and the print spooler on the same drive. I told people if they cleaned out their inboxes printing should work again, and it did. She returned a couple weeks later and fixed the problem in a more permanent way.

The legend tells of the 1403 dutifully printing that line by firing all 132 hammers at once, causing the chain to violently break and whipsaw itself out of the side of the printer cabinet.

It now makes sense why it cost $20,000/month (today's $) to use this computer, if you had to manually build each board, the cost for that alone is astronomical...

I think I owe my ECE 101 professor an apology.