Some years back I was IS manager for a company running an AS/400 for ERP, etc. By the time I left we'd converted most people over to PCs running terminal emulation or the screen-scraped GUI but initially they mostly had 5250 terminals. They were fairly robust but we had one start smoking first thing on a Monday morning,
No problem, get a spare one out, swap them over, the second one starts emitting smoke as well! Everywhere else in the office was fine but obviously I wasn't going to risk a third dead terminal so called the site electrician. When he'd finally tracked the wiring he found that socket was wired to a different circuit to the others and a fault meant it was running across two phases not 1 phase and neutral. It was a lucky escape, if the terminal had been left on when the user left on the Friday it could have had all weekend to smoulder away.