Many many years ago
In the CEGB where I was working we had a PDP 11/70 with 2 LP25 line printers. One of the printers worked flawlessly, the other glitched every 10 minutes or so. The DEC engineer turned up and tried to fix the problem - nothing showed on diagnostics - all voltages etc were correct. In desperation he tried swapping parts between the two printers to see which one caused the fault to move. He (and I) were astounded that the fault moved with the printer lid !! The lid was a large plastic part that did not come close to the electronics or any moving parts and both lids appeared identical to the naked eye !! Once a replacement lid was fitted, both printers stayed in good working order until the whole system was disposed of.
I still do not know what caused the problem.
Icon for what the lid did to the printer =========>
Biting the hand that feeds IT
