Had a pc out on plant connected up via RS232 running some in house emulation software.
Got a report that screen 'had gone silly' software incremenatlly updated different parts of the screen with plant status info, and it was all garbage.
Reset it, everything OK.
Following day same thing, and again.
Six days in a row, this is getting damn annoying. Terminal was three miles away, had to get all the safety gear on walk all the way down there.
Re intalled the software, changed the box, changed the terminal server port, no change...
Every day sometime between 5 & 6. In desperation went down there and watched the thing.
Boring, boring boring....
Lights came on, garbage.

They'd done some wiring work and wrapped the serial cable round the 440v power supply for the big fluorescents in the warehouse.....


Next week ?50,000,000 business stopped by vaacuum cleaner....