Re: Mysterious reboot every wednesday
A customer's mainframe had started to crash intermittently. It was decided to investigate properly when the engineers had their Saturday long maintenance slot.
Even though we were software support we had a suspicion that the culprit would be electrical noise from either the card reader or a tape deck. The customer had an exceptionally long row of tape decks - with new ones recently added.
We went along the row - opening and closing the door on each one to automatically load a tape. Sure enough one of them reliably crashed the mainframe after a few iterations.
When the senior engineer was free of his task of installing yet another new tape deck he came to see what we had found. Open/close tape deck door - no crash. It was clean - no problem.
Much scratching of our heads - and the engineer went back to his task. We tried again - crash!
This time we showed the engineer - and asked what he had done in the intervening time. All he had done was put a false floor tile back in place - which he had lifted earlier to facilitate threading the new tape deck's cable.
The tile was at the start of the row of tape decks. At that point there was a crowded run of thick tape deck cables sitting on top of each other. In each of the cables was a large metal junction box - and one of these from the previous week's tape deck addition was sitting on the pile of cables. It was so high that when the tile was in place it pressed on it slightly.
The false floor was an unusual design. Instead of "mushroom" pillars at the corners - there was a lattice of unpainted steel bars supporting the length of each tile's edges. The undersides of the tiles were reinforced with an unpainted steel sheet. The lattice was connected to the building "dirty" earth. Thus there was a connection between the lattice, the steel sheet, and the junction box - bridging "dirty" and "clean" earths.
Biting the hand that feeds IT
