What is diagnosis, as distinct from repair?

Select one answer.

• It is the act of replacing every component on a board one at a time until, eventually, the board happens to start working correctly again.
• It is the work of reasoning from a fault's observable effects to its underlying cause, ending in a known target before any part is changed.
• It is the paperwork done after a repair is finished, recording which parts were fitted so that the customer can be charged the correct amount.
• It is the same thing as repair, since finding a fault and fixing it are one single step that can never be usefully separated from each other.