Just a note, when I worked as a tech rep on Navy ships, 9 out of 10 times my service calls were to repair equipment that had failed, but the original failure was masked due to the ship board tech shotgunning the problem and just swapped and replaced components, all the while the excessive swapping of parts did more damage. I would have to fix what the techs did before going after the original fault.
Point: Take care when replacing parts.
Point well taken.
Have to say though that back in my day the subs could not go to sea without repaired and calibrated test equipment from our lab. As such, the equipment was returned in working order.
But that was our lab. Can't speak for any others and I don't doubt that happened. Interestingly, however, never saw a single factory tech rep in my seven years.
Just noticed I've been misspelling "Tektronix".