I was taught fault finding on airborne TX/Rx's in the early sixties. Box didn't work in the Vampire, into the radio bay, then inject the correct signal in the right place and the fault was isolated to half the box. Repeat until fault identified, valves, discrete components made it simple. Smell and signs of burning also were useful indicators.
Fast forward 50 odd years (some very odd) and can I use that training to fix my PC, no bloody chance. Event Viewer next to useless (for me) just tells me a hardware fault somewhere. Start swapping major components, luckily the PS is the first I try ( the cheapest) and fixes it. I don't envy current techs with the sort of faults mentioned earlier.