During the "Cold War" era, I was trained on most Valliant/Victor & Vulcan Radar Systems. When a defective "Black Box" came in, the first thing that I would reach for was my trusty oscilloscope & volt meter. There was no such luxury as diagnostics & we had to fault find down to component level i.e. resistor, capacitor or valve. What we would have given for integrated curcuits & diagnosing down to card level !
After leaving the RAF, I went on to develop computer products with a Multi National Company, where I was given the option to use low cost (knuckle dragging) engineers & a red button that would diagnose the problem & tell the engineer what to change, or use an expensive fully trained engineer with little or no diagnostics. It was a cost thing.
As far as parts procurement was concerned, I found the "VOG" (V-Bomber On the Ground) emergency request very good.