Mine would be more exotic, some sort of conflation of infra-red, Xray camera and pd monitor system that could capture images of properly functioning equipment. Different colours for the ac & dc currents in traces and different colours for the ac & dc voltages at nodes for some standard input etc. Then some "blink comparator" software that would immediately zero in on a likely problem area for the same piece of equipment , after you've taken an image capture. With an option to operate continuously and store any images when substantial changes occur , for those intermittant faults.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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