4 ms·

I was a mainframe systems programmer. Every so often the system would crash. Step 1 was to visit the machine room and look for the toolbox. The on-site IBM main

by daly 9y ago

I was a mainframe systems programmer. Every so often the system would crash. Step 1 was to visit the machine room and look for the toolbox. The on-site IBM maintenance guy would randomly power down and open cabinets to perform "preventative maintenance" so the system wouldn't crash due to hardware failures. Occassionaly he powered down our disk drives. One of the standard hardware debug methods was to 'swap cards' with a working unit. We had many controllers for our terminals (connected by coax to the office desks). When one failed they would swap cards with another controller until the first started working. Then they would order a new replacement for the failed card. As a result we had a 3-day outage. Each controller was purchased at a different time so the controllers had cards with different versions (different 'yellow wires' for patches). Eventually a bad combination of controller cards caused the channel (an IBM closet-sized box) to be confused. That caused the CPU to be confused (since it needed channel 0). So the CPU refused to boot, which IBM maintenance tried to debug by changing cards in the CPU. Sigh. We had to bring in one of the mainframe designers to debug it.

chris_st 9y ago
I was watching the VAX-11/780 at college get repaired by the DEC tech. She told me of her most difficult case: a randomly crashing 11/780. They checked everything (I believe she said that they eventually replaced every card!) and finally found a little piece of metallic gum wrapper -- it'd blow around in the fans and eventually bridge two pins, crashing the machine. They'd shut it down to look at it, it would settle to the wires above the fans, and wait its next chance. Glad I work in software :-)
- DrScump 9y ago
  Actual product slogan from the era: "Nothing sucks like a VAX" (VAX was a brand of vacuum in the UK, apparently. A colleague had a print ad with this slogan from a magazine on the wall.)
- WalterBright 9y ago
  I worked my way through college by wirewrapping prototype boards. The last step was to get a magnifying glass and carefully inspect the board, pin by pin, looking for any stray tiny bits of wire, or any wire hairs sticking out. For soldered boards, I'd examine for any tiny solder bridges. Doing that would save a ton of debugging time :-) Since wirewrapping is a long obsolete technology, here's what the boards looked like: https://microship.com/wp-content/uploads/1974/07/wirewrap.jpg https://microship.com/wp-content/uploads/1974/07/wirewrap.jp...
  - tsomctl 9y ago
    Wirewrapping is still done, it's pretty common for copper telephone lines and T1 circuits at the central office.
- cat199 9y ago
  Remember an ex-eastern bloc dev I used to work with telling me of his early days working with a soviet PDP-11 clone which required a logic board switch depending on the season since the temperature affected some transistors or solder - one card worked correctly in the winter, and the other in summer.. don't recall what they did for spring/fall or if these seasons were within tolerances for both cards..

by daly 9y ago

chris_st 9y ago

I was watching the VAX-11/780 at college get repaired by the DEC tech. She told me of her most difficult case: a randomly crashing 11/780. They checked everything (I believe she said that they eventually replaced every card!) and finally found a little piece of metallic gum wrapper -- it'd blow around in the fans and eventually bridge two pins, crashing the machine. They'd shut it down to look at it, it would settle to the wires above the fans, and wait its next chance. Glad I work in software :-)

DrScump 9y ago
Actual product slogan from the era: "Nothing sucks like a VAX" (VAX was a brand of vacuum in the UK, apparently. A colleague had a print ad with this slogan from a magazine on the wall.)
WalterBright 9y ago
I worked my way through college by wirewrapping prototype boards. The last step was to get a magnifying glass and carefully inspect the board, pin by pin, looking for any stray tiny bits of wire, or any wire hairs sticking out. For soldered boards, I'd examine for any tiny solder bridges. Doing that would save a ton of debugging time :-) Since wirewrapping is a long obsolete technology, here's what the boards looked like: https://microship.com/wp-content/uploads/1974/07/wirewrap.jpg https://microship.com/wp-content/uploads/1974/07/wirewrap.jp...
- tsomctl 9y ago
  Wirewrapping is still done, it's pretty common for copper telephone lines and T1 circuits at the central office.
cat199 9y ago
Remember an ex-eastern bloc dev I used to work with telling me of his early days working with a soviet PDP-11 clone which required a logic board switch depending on the season since the temperature affected some transistors or solder - one card worked correctly in the winter, and the other in summer.. don't recall what they did for spring/fall or if these seasons were within tolerances for both cards..